Autobiography of Xueming Yang

Abstract

Published as part of The Journal of Physical Chemistry C special issue “Xueming Yang Festschrift”. I was born in October, 1962, in the countryside not far from Hangzhou in Zhejiang Province, China. The area is famous for its lakes, rivers and canals and called “water town in southern China”, where most people live near rivers and lakes. The main mode of transportation in my hometown when I was a kid was by boat, so I learned early in my life about boat rowing and swimming in the rivers. My home village was located near a small river and not far from the Grand Beijing-Hangzhou Canal. Even though the village was only about 40 km away from Hangzhou, I never went to this beautiful and poetic city before I went to college. I started my elementary school in the spring of 1969, which is very close to my home village, only a 10 min walk. I spent five and a half years in the school. My elementary school years were during the Cultural Revolution period. I did not have much pressure from my family or from society to do well in the school. The most interesting thing that I remember from elementary school was the class before lunch, in which the teacher told stories from novels. During that period, I was also fascinated about stories told by an elderly blind gentleman, who often came to visit his relatives in the village. He was a famous fortune teller in the local area and seemed more knowledgeable than most people around. His stories made my countryside life more colorful as a young kid. After finishing elementary school, I went to middle school in the small town nearby, Xiashe, about a 40 min walk from my home. For a young kid, walking every day from home to school in the morning was a challenge. This is especially hard during the winter times and rainy days, when the roads were muddy and slippery. During those years, my father was the alarm clock in the morning to keep me going to middle school on time every day. I do not recall that I ever missed a single day of class during the four years in junior and senior high school. I am not so sure what really made me so persistent in going to school, maybe the little hope in my heart. In middle school, I started to have my first science classes, including mathematics, physics, and chemistry. However, English was not even in the curriculum in my high school years, so I started to learn English in college. In addition to the basic science classes, we also learned practical knowledge and skills that were more related to countryside life, such as how electric motors work, how to repair electric motors, and how to run farming tractors and to repair them. I also had a class that taught us how to do accounting for the collective village farm. These practical knowledge classes turned out to be very useful in the countryside. With the knowledge learned on these topics, it helped me to find problems such as why the electric motor-driven water pump was not working (when turning in the wrong direction). Looking back to those four years, my greatest accomplishment is that I passed the national entrance exams to get into a four-year college in 1978. It was certainly difficult to pass the exams. I never thought I could get into a college, because nobody in my home or my village had ever done that. But the most important thing that happened to me that related to my later scientific career is that I developed a strong interest in chemistry during that period, which set the stage for my pursuit of advanced degrees in chemistry. I have to thank Ms. Yueming Chen for her inspiring chemistry classes both in my middle and high school years. Her kindness and compassion were very heartwarming and made me felt that I was not so isolated from the society then. It was a very challenging period in my life in many aspects, since I almost could not go to senior high school due to my family background. Thanks to many teachers and kind people, their assistance and support in critical times provided me both confidence and hope to continue my study in those challenging times. Because of their unselfish help and encouragement, I also became a more optimistic and forward-looking person. I also had some interesting experiences in teaching some mathematics class for my fellow classmates, because the math teacher went to take the college entrance exams in 1977. It was a good self-learning experience for me that I had to learn the class materials before the lectures. At the end of my high school years, I was indeed fascinated about studying chemistry in college if I had a chance. However, I did not do well enough in the college entrance chemistry exam (85/100), so I missed a chance to study chemistry as a major in college. Instead, I did exceptionally well in the physics exam (95 of 100), which was a little unexpected. Because of this, I was admitted to become a physics major in Zhejiang Teachers College, now known as Zhejiang Normal University. It turns out that studying physics in college provided a good start for my scientific career, leading eventually to my becoming a researcher in the field of physical chemistry. The four years in Zhejiang Normal University constituted an important period of my life: I became a more mature and more optimistic person, and Chinese society also became more open. In addition to the academic classes, I had many pleasant times on the basketball court with my classmates. In 1978, Zhejiang Teachers College was still a small college, but I had a very solid college training in physics. Most of the professors and lecturers were very dedicated and helpful. I also learned how to self-study during that period, which I realized later was probably the most important skill to have in life. Because of the need to learn quantum mechanics for the national graduate entrance exams before the scheduled quantum mechanics class, I made an effort to self-study the subject with the help of Prof. Henian Li. In my senior year, I was encouraged by Prof. Desheng Chen to do a graduate thesis on statistical physics and had my first taste of research. This experience cultivated my desire to pursue further advanced study in science. Near the end of my college years, I started to think about what to do next. Most graduates from my school were given teaching jobs in high schools. That was a very stable career path, but I was not ready then to take a lifetime teaching job in high school. I want to make a try to see if I could get into a graduate program, even though the chance to do that was quite slim. In 1982, the whole country admitted about ten thousand graduate students, and there were about 300k graduating college students. The only way at that time to get into a graduate program was to take the exams for graduate schools. When I was going through the graduate program catalogs for all Chinese universities and research institutes, one institute got my attention, i.e., Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences. I found one direction particularly interesting, chemical laser modeling, at DICP. The advisor of this direction is Prof. Cunhao Zhang, who was already very well-known. This was a very attractive direction to me because it involves both chemistry and physics, which matched my desire to study more chemistry in the future because of my original interest in chemistry in high school. So I decided to take the exams for this particular graduate program. I was truly excited to learn that I got into the graduate program of DICP in the early summer. This step opened a new chapter of my scientific education, and it certainly had a huge impact on my future career. I took a long train from Hangzhou to Dalian, via Beijing, in late August 1982. The whole trip took about 48 h to get to Dalian. I enrolled in the graduate program in the Dalian Institute of Chemical Physics, CAS. I immediately fell in love with this beautiful city after I arrived, and Dalian has always been a special city for me. I became a graduate student in the group of laser spectroscopy of DICP. Initially, I had two advisors: Prof. Cunhao Zhang and Prof. Zhiyi Shen. Prof. Cunhao Zhang was also already a leading scholar in laser spectroscopy, molecular dynamics, and chemical lasers in China. Even though originally I was attracted to the direction of chemical laser modeling, I eventually ended up in studying laser spectroscopy, which was a great choice for me. It provided a solid foundation for my research in the future. About a year later, Prof. Qingshi Zhu joined the laser spectroscopy group, and he also became an advisor for my master degree thesis. He had just returned from the United States as a visiting scientist at MIT and UC Santa Barbara. He taught us a course of molecular spectroscopy, which was very helpful. During that period, I investigated high-resolution infrared spectroscopy for several polyatomic molecules using both a high-resolution diode laser absorption spectrometer and a Fourier transformation spectrometer. I learned how to assign the spectral lines and fit them to a spectroscopic model to obtain the molecular constants for specific transitions. The molecular spectroscopy knowledge that I learned during that time is essential for my later scientific research in molecular reaction dynamics. Molecular spectroscopy was my gateway to a long scientific career in physical chemistry. I feel quite fortunate that I started my scientific research training this way with these excellent research advisors. During that period, I remember that I had received two good pieces of advice that had a lasting impact on my career. One was from Prof. Cunhao Zhang. He said that, as a new graduate student, one should devote most of your time to your own research project but should also spend some small amount of time to try to study other related topics and gradually you should increase this time to broaden your knowledge in science. I found this advice particularly helpful in my practice. Another good advice was from Prof. Qingshi Zhu, he told me as a young scholar, one should not try to publish research works hastily and should always try to publish high quality works. This point was well taken in shaping my own research philosophy. I probably did not realize the importance of this advice at that time, but at a later time, I found this advice was very helpful in my research career development. In the middle of 1980s, the government started to allow students to pursue advanced graduate studies abroad, even for students who do not have any relatives outside of the country. In early 1985, I graduated with a master degree and passed exams to get into a doctoral program at DICP. The prospect that I would have a chance to do advanced doctoral research drove me and many of my fellow classmates in DICP to apply for graduate studies in US universities. I was accepted to the graduate program at the University of California at Santa Barbara with the intention to study in the group of Prof. David Harris group, who specialized in high-resolution molecular spectroscopy of unstable molecules using laser-induced fluorescence method. This was the direction that I was very much interested in then. I arrived at Santa Barbara in October, 1985, via San Francisco. After spending a couple of days in Palo Alto with Rong Zhang, who was my classmate at DICP and then a graduate student at Stanford in Prof. Richard Zare’s group, I took the Greyhound bus from Redwood City to Santa Barbara. Because I was late for the registration for the fall quarter at UC Santa Barbara, I started in the winter quarter as a graduate student. In the first year, besides taking the graduate courses, I started to take the Ph.D. qualification exams, the so-called Cumulative Exams in chemistry at Santa Barbara. Without too much difficulties, I passed the qualification exams and became a Ph.D. candidate in the second year. At that time, Prof. Richard Martin, who was teaching the chemical dynamics class, offered me a position in his group in surface chemistry research. Because my background was mostly in the gas phase spectroscopy and dynamics, I was not so sure that I wanted to pursue surface chemistry research. Even though I did not join his group, I was truly grateful to Prof. Martin. In the spring of 1988, as I was looking for a possible new direction, Prof. Martin told me that a new faculty search in physical chemistry at the chemistry department was in the process. I remembered that I went to all the seminars given by the candidates who were interviewed for this position. One of the candidates was Dr. Alec Wodtke. In his seminar, I learned his research plan was to study spectroscopy and dynamics of highly vibrationally excited molecules, which was quite appealing to me. Later, I learned that Alec was hired and would come to the department in August. On his first day in the department, I found Alec in Prof. Martin’s office and I expressed my strong interest to work in his new group. I did not think that I had impressed him enough in our conversation, as he had not promised to accept me as his student at the end of the conversation. Probably, I was looking a little bit desperate because I was very eager to make a change. Alec told me that I should think about it for a week if I really wanted to join his laboratory. In any case, that was not a bad result for me. I thought at least Alec did not refuse my request to become his student. I was persistent because that was what I really wanted to do. One week later, Alec accepted me as his first student. Over the next three years, I worked in Alec’s group and helped to build the research laboratory from the beginning. This was an extremely valuable experience for me. I learned how to do research and how to find interesting scientific questions in that period. Most significantly, Alec’s great love for science had truly inspired me. I found great pleasure and intellectual inspiration in doing scientific research in Alec’s group. I mainly worked on three research projects in Alec’s lab. The first experiment I carried out was the laser-induced predissociation spectroscopy study on the Schumann–Runge band of O₂ in an open atmospheric flame with a special tunable argon fluoride laser from Lambda Physik, which was the secret weapon in Alec’s laboratory then. Line shapes were measured for certain O₂ rotational transitions in the Schumann–Runge band and then modeled using a sophisticated predissociation model. These results showed that orbit-rotation interaction between the B ³Σ_u^– state and the ³Π_u continuum plays a significant role in the predissociation of the B-state. The second project I worked on was the spectroscopy and dynamics of highly vibrationally excited nitric oxide (NO) using the stimulated emission pumping (SEP) method. We investigated the SEP spectra of NO up to v = 24, and studied the dynamics of vibrational energy transfer of these highly excited molecules with its ground state molecules. Interestingly, we found the vibrational relaxation rate of NO(v) increases very rapidly as vibrational excitation rises. State-to-state relaxation rates were also measured. The experimental studies and literature readings gave me an in-depth understanding of molecular vibrational relaxation dynamics. The third project I worked on was the SEP spectra of HCN, which is the simplest isomerization reaction system. I was always interested in the dynamics aspect of molecular spectroscopy since my time in Dalian. In the literature search, I found that the HCN was an interesting system that would give us the opportunity to investigate the isomerization process (HCN ↔ CNH). Through the study of spectroscopy of highly vibrationally excited molecules, one can investigate the potential energy surface as well as the isomerization dynamics. Incidentally, there was an absorption band of HCN in the spectral range of the argon fluoride laser. With that in mind, I proposed to Alec that we should study this system using the SEP method. This project was very successful and received quite a bit of attention in the molecular spectroscopy community. From this project, I also learned the nature of isomerization reaction at the very fundamental level. Looking back to those five and half years at Santa Barbara, I was fortunate that I had experienced difficulties in the early stage and eventually found my way to complete my Ph.D. education. Besides learning the experimental techniques and research skills, I learned how to look for interesting scientific problems to work on. I gained confidence in doing scientific research, which was invaluable for my career development. I was very grateful that I had the opportunity to work in Alec’s group. Amazingly, we are still collaborating with each other on interesting problems after all these years! In my Ph.D. thesis, I had quoted the renowned ancient Greek tragedian Aeschylus’s famous words, “when a man is willing and eager, the gods join in”. This quote expresses very well my experience at Santa Barbara. Alec certainly had provided the primary drive and support for my Ph.D. education. After getting my Ph.D. in the summer of 1991, I spent one year and eight months in Princeton as a postdoc in Giacinto Scoles’s and Kevin Lehmann’s laboratories. This provided me a great opportunity to study high-resolution IR spectroscopy of molecular clusters using the highly sensitive bolometric detection technique. I worked on high-resolution IR spectroscopy and predissociation dynamics of many interesting hydrogen-bonded clusters, such as HCN-HCCCCH, HCCCN-HCCH, HCCCN-HCCCN, and (HCCCN)₃, with other group members, including Erik Kerstel, Joan Gambogi, and Brooks Pate. The predissociation dynamics of these hydrogen-bonded clusters was an especially interesting topic for me. During that period, I also had an opportunity to work for a week in Prof. Roger Miller’s lab with his student Ray Bemish at the University of North Carolina at Chapel Hill on the IR spectroscopy of HCCCN- and HCCCCH-related clusters using their experimental apparatus. That was a memorable working experience for me. During the period at Princeton, I started to give some serious thinking about what I really wanted to do in the future. I felt that I had not found an exciting direction on spectroscopy that I wish to focus on in the future. But one thing was clear that I wanted to try to stay on the academic research track. At the end of 1993, some funding problems for my postdoc support appeared, and this compelled me to look for possible positions in a relatively short period of time. Fortunately, I received a quick offer from Prof. Yuan Lee at Berkeley. This opening involved designing and building a new crossed-beams apparatus to study chemical reaction dynamics using the VUV synchrotron radiation ionization detection at the Advanced Light Source (ALS), the world’s first third-generation synchrotron facility. A chance to build a new and complicated scientific machine was very appealing to me, and I decided to take on this new direction. This move also gave me a chance to change my research direction from molecular spectroscopy to chemical dynamics. I was quite excited about this move because Alec was also involved in the chemical dynamics beamline project. He was one of the spokespersons for the beamline. Shortly after I arrived at Berkeley, Arthur Suits became the director of the chemical dynamics beamline. Before I moved to Berkeley, Yuan Lee suggested to me that I should visit Berkeley first to get a complete set of the drawings for the rotating source machine in his laboratory and get a workstation from LBNL, then go to Santa Barbara to design machine with Alec. I went to Berkeley at the end of April, 1993, and did just that, and then I went to Santa Barbara to start to design the machine for the beamline. Over the next seven months or so, I worked quite hard to design the new machine using the ME30 3D CAD program from HP. I became quite fascinated with mechanical designing using this powerful CAD program, and for many years after that, this program was a major tool to design experimental apparatuses in my own lab. During this period, I had many discussions with Alec, and quite a few times with Yuan. I learned a few important facts from them about the crossed beams techniques: always try to get a larger signal, lower the background, and increase reliability. These are the three golden rules that have guided me in developing new scientific machines in my own lab. After I finished designing the new machine for the ALS chemical dynamics beamline, I moved to Berkeley to start to build the machine. Using the CAD program, I translated the 3D machine into detailed 2D mechanical drawings for procurement purposes. It took many months for me to find a company that was willing to make the vacuum machine with rotating source chambers and double beam sources. During this process, I got significant help from the engineers in the LBNL Engineering Division and machine shops. This unique experience greatly improved my engineering skills in building new scientific instruments. After getting all the parts and vacuum chambers, we started to put the machine together. Around that time, a new student, David Blank, from Prof. Lee’s group joined this project. David Blank, Arthur Suits, and I worked hard to put the machine together in a relatively short time. During that period, I also helped to build the gas filter for the chemical dynamics beamline. I also paid close attention to the beamline as well as the ALS synchrotron facility and also learned the concept of free electron lasers. This experience provided me an excellent opportunity to look into this new emerging field, which has made great impact on my research later in Dalian. After getting the machine to work, we performed a few experiments on photodissociation of several polyatomic molecules to demonstrate that this machine could perform well and published a paper in Rev. Sci. Instrum. for this apparatus. Even though I did not publish many papers over this period, I did learn how to build complicated experimental apparatuses with high standards and also started to appreciate the importance of developing advanced instruments in experimental physical chemistry research. This invaluable experience had a profound impact on my entire scientific career. From then on, I went on to build seven more molecular beam machines and a number of surface photocatalysis instruments. These instruments have played key roles in the studies of chemical reaction dynamics in my research laboratory. The idea to try to build a VUV free electron laser (FEL) later in Dalian also originated from my experience at the ALS chemical dynamics beamline, because I realized that a VUV FEL would provide a much stronger VUV light for dynamics studies than a third generation synchrotron light source. Near the end of my postdoc in Berkeley, Yuan asked me if I wanted to take a position at the Institute of Atomic and Molecular Sciences (IAMS) in Taipei, to help build a new crossed molecular beams laboratory. I realized that this was a great opportunity for me to do cutting edge chemical dynamics research, so I took the offer and started a new academic life in Taipei in December, 1995. My first project was to build a new universal crossed molecular beams apparatus, in collaboration with Yuan Lee and Yuan Lee’s NTU student Jr-Min Lin, aiming to study dynamics of elementary chemical reaction with highest sensitivity. The grand strategy was as much as possible to enhance the sensitivity and reduce the detector background in this machine. A larger quadrupole system with 1.25 in. diameter rods was developed based on the commercial Extrel quadrupole mass spectrometer. The largest quadrupole available was with 0.75 in. rods. For detection of small molecular species, this larger quadrupole system could increase the detection sensitivity by about 3 times. We also developed a cryogenic pump by cooling an oxygen-free copper block with larger surface area to liquid helium temperature to reduce the residual gas background (mainly H₂) in the ionization detection region by more than an order of magnitude. An ultimate pressure of 1 × 10^–12 Torr in the universal detector was achieved in this machine. The successful development of this apparatus provided a new venue to study dynamics of more complex chemical reactions, especially those reactions with multiple reaction channels. A typical example is the O(¹D) reaction with methane. In this multiple-channel reaction, only one channel had been observed previously using similar apparatus. However, using the new universal crossed beams machine, we detected three major channels: CH₃ + OH, CH₂OH + H, and HCOH/H₂CO + H₂ with clear identification of HCOH and H₂CO products. Many more complex reactions with multiple channels have been investigated with this new apparatus, which opened a new venue in this research direction. Before moving to IAMS, I was also reading about the H atom Rydberg tagging technique developed by Welge and his collaborators. It had then already shown great potential in studying quantum dynamics of molecular photodissociation and elementary chemical reactions because of its high sensitivity and high time-of-flight resolution. After arriving at Taipei, I decided to pursue this direction. When the universal crossed beams machine was nearly completed, I started to design our first Rydberg tagging apparatus. When the machine was finished, our first test experiment was on VUV photodissociation of the water molecule. The experimental project went very well: it provided the most detailed dynamics information on the VUV photochemistry of H₂O at 121.6 nm, and the key of this experiment was to make a clean monomeric H₂O molecular beam in which H₂O can easily become clusters. This project also led to a fruitful collaboration with Prof. Richard Dixon at University of Bristol. Experimentally, we have observed an interesting product (OH) population oscillation, which was attributed to quantum interference between two conical intersection pathways through theoretical dynamics analysis by Richard. Photodissociation of H₂O in the broad VUV region has been carried out over the next the two decades in our laboratory and led to detailed mapping of the dissociation dynamics of H₂O via different electronic states. H₂O photodissociation provides an excellent benchmark for quantum dynamics of molecular photochemistry. The initial target reaction of the new Rydberg tagging machine is O(¹D) + H₂ → OH + H. The design of the apparatus was optimized for this reaction, in which the O(¹D) beam was generated by photodissociation of O₂ using the 157 nm laser. The full product (OH) quantum state resolved differential cross sections were mapped for this reaction, providing an excellent test ground for this typical insertion reaction at the quantum level. Around the time we were performing the O(¹D) reaction experiment, Prof. George Schatz was visiting IAMS, and we thus started a fruitful collaboration on this reaction. His quasi-classical calculations of the vibrational and rotational state distributions of the OH product were in good agreement with the experimental results, providing a deep understanding on this typical insertion reaction. Using the apparatus, we also carried out a detailed experimental study on the H + HD → H₂ + D reaction, an interesting forward scattering peak for this reaction. When I was visiting JILA as visiting fellow, I had an opportunity to talk to Prof. Rex Skodje and started a long and fruitful collaboration on quantum dynamics of elementary chemical reactions. His quantum dynamics analysis shows that the forward peak observed was attributed to a time-delay mechanism due to slowing down on specific quantum bottleneck reaction pathways, not a reaction resonance mechanism. Using the same apparatus, we also observed experimental evidence of quantum bottleneck states in H + D₂ → HD + D. This collaboration also really got me interested in the topics of quantum bottleneck states and reaction resonances. During the period at IAMS, I was involved in a third research project to build a new crossed molecular beams scattering machine on the VUV beamline at the synchrotron facility (NSRRC) in Hsinchu, which is a 1.5 GeV machine. This project was similar to the chemical dynamics beamline at ASL. Initially, I was not fully convinced we could make further improvements on the Berkeley machine. After three months of intense design work done by myself, I came up with a more compact design in the detector. With application of the ultrahigh vacuum technique and the larger 1.25 in. quadrupole mass spectroscopy system already used in the universal crossed beams machine, I was convinced this apparatus should have a noticeably better performance than the machine at ALS. The new apparatus was used to study molecular photodissociation initially. The machine later was taken over by Dr. Shi-Huang Lee at NSRRC, and he carried out many interesting crossed beams experiments on reactions related to carbon species using this apparatus. The above three projects at IAMS were all quite successful and these instruments opened new possibilities in chemical dynamics research and certainly pushed my own research work in molecular photochemistry and bimolecular reaction dynamics to a new level. In 2001, I received an offer to join the State Key Laboratory of Molecular Reaction Dynamics from the Dalian Institute of Chemical Physics (DICP). After consulting with Yuan Lee and Kopin Liu, I made a decision to take the offer and began to build new research laboratories at DICP from 2002. In early 2004, I finally moved to DICP and started a new phase of my academic life. Over all the years at IAMS, I received very strong support from Yuan Lee, Kopin Liu, and Sheng-Hsien Lin, for which I am very grateful. I also had a very good time working with many talented and hardworking students and postdocs at IAMS during that period. The eight years in Taipei were certainly a very rewarding experience in my life. Over the period moving from Taipei to Dalian, I began to think about future interesting research problems. After reading all the works done previously in the Lee group and by Kopin Liu and Rex Skodje around 2000, I started to get seriously interested in the issue of reaction resonances in chemical reaction. Therefore, we decide to build a new crossed molecular beams apparatus with a rotating molecular beam source using the H atom Rydberg tagging technique (RT2), which would allow us to measure quantum state resolved differential cross sections for many elementary chemical reactions with variable collision energies. I was especially interested in studying reaction resonances at very low collision energy. The new Rydberg tagging machine was finished and ready for experiments in 2004. In addition, I was able to move the vacuum chamber of the Rydberg tagging machine at IAMS to DICP and we rebuilt the whole apparatus (RT1) in the new lab at Dalian. We therefore had two Rydberg tagging machines operating in our lab, which can perform different types of experiments. Using these two apparatuses, we carried out interesting experimental studies on many elementary chemical reactions. One of the most interesting research directions we pursued was the study of reaction resonances in the F + H₂(HD) reactions. In 2005, using the RT2 machine, we measured the full quantum resolved differential cross sections for both the F + H₂ → HF + H and F + HD → HF + D reactions, providing the most accurate experimental data on this benchmark reactions for reaction resonances. Around that time, I got to know Prof. Dong Hui Zhang at National University of Singapore; he was a renowned expert on accurate quantum dynamics theory and calculations. Gradually I realized that he is one of the best in the world to perform highly accurate full quantum dynamics calculations on the elementary reactions that I was studying, so we started to collaborate soon after I moved to Dalian. In 2006, Dong Hui also joined the State Key Laboratory of Molecular Reaction Dynamics at DICP; this began a remarkable partnership between theory and experiment over the next decades. His strong commitment to making the most accurate reaction dynamics calculations on elementary chemical reactions was exactly what we needed to interpret the accurate experimental results for the F + H₂ → HF + H and F + HD → HF + D reactions. Based on a highly accurate potential energy surface (PES) developed by Donghui and Daiqian Xie from Nanjing University, Donghui calculated the full quantum differential cross sections for the F + H₂ reaction, and the theoretical results were in very good agreement with our new experimental results. At the collision energy we investigated, this reaction was dominated by the excited resonance state, which was very well characterized. However, the theoretical results based on the same PES were not in very good agreement with the experimental results for the F + HD → HF + D reaction at the low collision energies, which was predominated by the ground resonance state. A more accurate version of the PES was then developed by Donghui and Xin Xu (Fudan University) with better characterization of the ground resonance; the full quantum theoretical dynamics results based on this PES were in much better agreement with the experimental results for the F + HD → HF + D reaction. A highly accurate physical picture of the reaction resonances in this benchmark system had thus emerged. The energy position of the resonance states was determined with an accuracy of about 0.01 kcal/mol, significantly better than chemical accuracy. Through experimental measurement, we can also accurately determine the lifetimes of the reaction resonance states. For the F + p-H₂ → HF + H reaction at low collision energy, our crossed beams results were also compared with the negative ion photodetachment spectra from Dan Neumark, and the agreement was quite remarkable. Our results indicated that chemical reactivity of this reaction at low temperatures mostly originated from resonance induced tunneling, while these transient resonance states are located mainly in the exit channel. Using the RT2 machine, we have also studied the Cl + HD(v = 1) → HCl + D reaction. In collaboration with Donghui’s theoretical calculations, we have demonstrated reaction resonances near the barrier region can also be detected and characterized. These resonances are caused by the chemical bond softening mechanism. Preliminary results in a recent study on the F + H₂ reaction shows that reaction resonance can also exist in the entrance channel. This suggests that reaction resonances could exist in the entrance channel, in the barrier region, and in the exit channel. In addition, resonances are found now in many more reactions, indicating that reaction resonance is not a rare phenomenon, rather it is quite ubiquitous in chemical reactions. Through high-resolution scattering experiments in close collaboration with highly accurate quantum dynamics theory, my understanding of reaction resonances was significantly enhanced. This is a truly rewarding discovery experience in my career. In this process, I have learned most of my theoretical knowledge from Donghui, and he has made great contributions to the development of this program in our laboratory. Over the past decade or so, I was involved in another interesting reaction dynamics project: the geometric phase effect in chemical reactions. About 15 years ago, I was reading the original geometric phase (GP) effect paper in 1979 by Mead and Truhlar. Their paper had shown that, in a chemical reaction with a conical intersection such as the H + H₂ reaction, if one neglects the excited upper cone, the quantum mechanical solutions under the Born–Oppenheimer approximation are not rigorous, unless a geometric phase term is included. The interesting question is whether including this geometric phase or not will affect a chemical reaction. I started to get really interested in this question and tried to look for a good experimental method to detect this effect. After reading the early works by Dick Zare (Stanford) and Stuart Althorpe (Cambridge), I realized that detecting oscillation in the angular distribution for a reaction product at a specific quantum state was likely the best way to experimentally detect the GP effect. I thought that the high-resolution velocity map imaging method might be the best chance. When Prof. Xingan Wang, a former student from my lab, joined the Department of Chemical Physics at USTC, I suggested to him that we should build a high resolution imaging machine to study the GP effect in the H + H₂ reaction. Xingan also got very excited about this idea, so we started to build this new imaging machine. The initial target reaction is the H + HD → H₂ + D reaction. In two years, Xingan with the student Daofu Yuan built a beautiful crossed molecular beams imaging machine. They improved considerably the resolution of the H atom product by using the (1 + 1′) threshold ionization. With this machine, they first measured successfully the differential crossed sections of the H + HD → H₂ + D reaction at 1.35 eV. By comparing with the theoretical results from Donghui’s group, we found there is no geometric phase effect in this reaction at this collision energy, which is much lower than the conical intersection energy (2.73 eV). After we increased the collisional energy to 2.77 eV, a beautiful crossed beams scattering image was also measured. In comparison with the theoretical results, the geometric phase effect on the angular distributions was clearly observed. Geometric phase effects were later detected at collision energies below 2.0 eV using both imaging and Rydberg tagging techniques. The most interesting result from this work is that the GP effect can be used to uncover the distinctive dynamics pathways near the conical intersection. Most of my research has been in the area of molecular photochemistry and reaction dynamics in the gas phase. My home institute, Dalian Institute of Chemical Physics, has always been very strong in surface catalysis. Since I moved to DICP, I always wanted to do something in this direction. One particular research area got my attention. Around that time, there were many papers published on the topic of water splitting. In most of these works, they added a so-called sacrificial agent, methanol, in the sample to produce hydrogen, so my immediate question is what the role of methanol in water splitting is. Around this topic, we built three experimental instruments almost simultaneously: 1) the 2PPE apparatus to study electronic structures using the 2PPE technique by Zefeng Ren and Chuanyao Zhou; 2) the universal surface photocatalysis instrument using the ultrasensitive mass spectrometer by Qing Guo and Zefeng Ren; and 3) the STM photocatalysis machine by Zhibo Ma. Using the 2PPE technique, also in collaboration with the STM group led by Profs. Jianguo Hou and Bing Wang at USTC, we found that methanol can be photocatalyzed at 400 nm on the TiO₂(110) surface. We further investigated mechanisms of methanol and water photocatalysis on TiO₂ surfaces using the universal mass spectrometer photocatalysis instrument and the STM photocatalysis machine. We discovered that methanol and water photocatalysis are strongly wavelength dependent. At 400 nm, methanol can be photodissociated efficiently, while water cannot be dissociated. Water can only be dissociated at wavelengths below 300 nm, and with a very different mechanism from methanol. More interestingly, we found that hydrogen bonding between water molecules on the surface can hinder the photocatalytic water splitting. From these studies, we concluded that surface catalysis cannot be understood merely using an electron–hole separation model; instead, surface reaction dynamics also play a critical role in photocatalysis. I believe more surface chemical dynamics studies are needed in order to establish an accurate physical picture for surface photocatalysis. For experimental chemical dynamics studies, innovative scientific instruments are critical. Over my entire scientific career, I made great efforts to develop the most advanced instruments to solve important scientific problems that I am interested in. In addition to various new instruments developed, we are also very interested in acquiring new and powerful lasers to make molecular detection and excitation more efficient. When I was a postdoc at Berkeley, I realized that the VUV light synchrotron source is a way to ionize molecular species, but its application in dynamics are limited because of its relatively low intensity. Since then, I paid close attention to the development of the high-gain free electron laser (FEL) technology, which would produce strong VUV and X-ray laser light. Around 2000, two mechanisms of high-gain FEL, HGHG and SASE, have been demonstrated by groups at Brookhaven and Argonne. New FEL projects were initiated in many countries, such as Germany, US, Japan, Korea, and Switzerland. There were also proposals in China to build a FEL facility. Around 2009, I got an invitation to attend a workshop in Shanghai to discuss possible scientific applications for the SDUV-FEL facility at the Shanghai Institute of Applied Physics, CAS. The SDUV-FEL project was led by Zhentang Zhao and Dong Wang. The wavelength of this facility was optimized in the 300 nm region, which was not very interesting to our lab. I therefore proposed to Zhentang Zhao and Dong Wang that we should build a true VUV FEL at Dalian for our research lab. So we immediately started to plan and design this project in collaboration. After much effort, we eventually got the VUV-FEL project funded by the National Natural Science Foundation of China. The Chinese Academy of Sciences also provided support for the FEL facility building via national infrastructure funding. The VUV FEL facility was commissioned successfully at the end of 2016. The FEL is tunable from 50 to 150 nm, providing a unique and strong light source for experimental studies in frontier research. The development of this facility opened many new possibilities in many research areas such as molecular photochemistry, neutral cluster spectroscopy, surface catalysis, and biomolecule photodissociation mass spectrometry. I am very happy to see that top scholars in dynamics, such as Mike Ashfold and Alec Wodtke, are now starting to use this facility to do interesting experimental study. A few recent examples of research using this facility are mentioned here. In molecular photochemistry, a direct O₂ formation channel was detected from VUV photodissociation of SO₂; this process may be relevant to the Big Oxygen Event in the early Earth’s atmosphere. Using this facility, a unique infrared spectroscopy method for neutral clusters has also been developed, investigating neutral water clusters from small to large and providing new structural information for these clusters. Recently, the light source was also used to probe radicals from single atom catalysis processes and to investigate atomic scattering dynamics from surfaces. Finally, the development of a VUV FEL photodissociation mass spectrometry method provides a new tool to study interactions between drug molecules and proteins. These advances in different directions suggest that Dalian Coherent Light Source (DCLS) has wide applications much beyond physical chemistry. The development of DCLS also lays a solid foundation for a promising new superconducting soft X-ray FEL project in Shenzhen with enormous scientific applications. Looking back to my scientific journey, I feel very fortunate that I had discovered a path to the frontier of physical chemistry research. Over the years, I became a strong believer of the ground rule in experimental physical chemistry research, i.e., ones need to develop innovative and advanced instruments to solve important physical chemistry problems. The longer I am in this field, the stronger I believe this rule. In practice, I have also followed this rule diligently in my research pursuits in this field. In addition to this, I was always trying to answer the key scientific questions in my research field with unique instruments developed in our own laboratory. Before I decided to get into a research problem, I would always ask myself the following question: if and how can we make a unique contribution to solutions in this research direction? If a scientific problem became clear, we would always make a great effort to build a new experimental apparatus that has a unique capability to attack the problem. I have been involved in developing more than a dozen new instruments and a VUV free electron laser over the last three decades; these instruments have played key roles in the advances made in a few frontier topics, such as reaction resonances, geometric phase effects, photocatalysis at single molecular level, and photochemistry of H₂O and SO₂ etc. The making of Dalian Coherent Light Source has also significantly broadened my research horizon much beyond chemical dynamics. Over the last two decades or so, I had many opportunities to collaborate with world renowned scholars in the field: Richard Dixon, George Schatz, Dan Neumark, Mike Ashfold, Rex Skodje, Tim Minton, Piero Casavecchia, Donghui Zhang, Xin Xu, and Daiqian Xie. The collaborations with them have certainly elevated my research to a new level. I have learned a great deal from these collaborations, especially those with theoreticians. Here, I would like to thank all my collaborators, who surely made my scientific career more interesting and exciting. Over the years, I really enjoyed attending many international meetings and academic visits. I also have made my services available to the academic community by organizing international and national dynamics meetings and being an editor for scientific journals. These activities have eminently benefited my research works and greatly broadened my scientific horizon. I want take this opportunity to send my gratitude to all my teachers and mentors, especially Yueming Chen, Henian Li, Desheng Cheng, Qingshi Zhu, Cunhao Zhang, Alec Wodtke, Giacinto Scoles, and Yuan Lee, who provided great inspiration and guidance in my science education and training. I also want to thank Kopin Liu, a special mentor and a friend for much of my academic life. I wish to acknowledge all my students and colleagues, who made immense contributions to the research projects in our laboratory. Special thanks to Alec and Donghui for their long friendship and stimulating collaborations. I also want to express my sincere thanks to the funding agencies which supported my research over the last three decades, especially the National Natural Science Foundation of China, Ministry of Science and Technology, and Chinese Academy of Sciences. Finally, I wish to thank my family, especially my sister, my children and my wife for their unwavering love and support in my pursuit for a wonderful scientific life. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.4c07062. Publications of Xueming Yang (PDF) Curriculum Vitae of Xueming Yang (PDF) Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html. Views expressed in this Preface are those of the author and not necessarily the views of the ACS. This Preface is jointly published in The Journal of Physical Chemistry A and C. This article has not yet been cited by other publications.