Looking Backward and Forward

Abstract

Published as part of The Journal of Physical Chemistry C special issue “Alec Wodtke Festschrift”. have the courage to try new things about which you may be ignorant. do not worry what others think. recognize that you cannot succeed without some luck and remember that 1) and 2) seem to help with 3). Figure 1. My First Building Project. The Experimental setup for the F+HD experiments. The effusive F atom source (6)–I am still proud of it–and the velocity selector (8) produced a slow F atom beam (7) with a narrow velocity spread. The H₂, D₂, and HD beams (5) were cooled with liquid nitrogen (3) to achieve best conditions. The small velocity of the F atom beam made the entire scattering map visible in the experiment. Its low intensity also reduced the signal substantially. The project was led by Dan Neumark as part of his Ph.D. thesis work. Figure reprinted from ref (1). with the permission of AIP Publishing. Copyright 1985 AIP Publishing. Figure 2. The first vibrationally state resolved differential scattering distributions of a chemical reaction. Note that HF(v = 3) is scattered forward while HF (v = 2) is scattered backward. Figure reprinted from ref (1). with the permission of AIP Publishing. Copyright 1985 AIP Publishing. Figure 3. The reaction path for nitromethane decomposition: (left) the relative energies of the simple bond rupture reaction and isomerization were deduced from the IRMPD data obtained with the rotating source machine in 1986. Figure reprinted with permission From ref (12). Copyright 1986 American Chemical Society. Those results agree well with (right) electronic structure theory calculations by MC Lin possible in 2013. Figure reprinted with permission from ref (10). Copyright 2013 American Chemical Society. Figure 4. This probably got me tenure: Laser-induced fluorescence spectrum of HCN obtained in the near Vacuum Ultraviolet using a Tunable ArF laser. Once this spectrum had been seen in the lab, stimulated emission transitions quickly followed. Figure reprinted with permission from ref (23). Copyright 1990 Optica Publishing Group. Figure 5. My first beam surface scattering experiment. (left panel) Dick Martin’s instrument. See ref (27). for details. (right panel) The spectrum obtained when monitoring electron emission as a function of laser wavelength. The observed transitions are assigned to the CO Cameron system. This is a way to measure the speed distribution of individual quantum states of molecules. Figures reprinted with permission from ref (27). Copyright 1992 AIP Publishing. Figure 6. Born–Oppenheimer Failure: Electron emission resulting from NO(v = 18) collisions with the Cs/Au(111) surface. Electron emission is detected simultaneously with DUMP laser’s wavelength for two PUMP transitions. We compare these spectra to fluorescence depletion (down-going signal) spectra observed under identical conditions. The observed spectral resonances agree with known transitions of NO to better than the line-width of the laser. Figure reprinted with permission from ref (56). Copyright 2005 Springer Nature/Macmillan Magazines Ltd. Figure 7. Six years of being department chairman will give you another view of yourself. This image is used with permission from the Department of Chemistry and Biochemistry of UCSB. Figure 8. Using the RAT machine to study H scattering from graphene. (A to C) Experimentally derived scattering distributions. (D to F) Classical trajectory simulations employing a full dimensional PES. (G) Trajectory Analysis. Trajectories shown in red cross the barrier to C–H bond formation whereas those shown in black do not. Figure reprinted with permission from ref (82). Copyright 2019 The American Association for the Advancement of Science. Figure 9. Quantum mechanical tunneling of up-side down CO converting to right side up CO on NaCl at 20K. The fastest tunneling rate occurs for ¹³C¹⁶O and the slowest for ¹³C¹⁸O. Remarkably, the lightest isotopologue ¹²C¹⁶O exhibits a rate between the others. Figure reprinted with permission from ref (91). Copyright 2022, the authors. Figure 10. The first velocity resolved kinetics experiment. (Left Panel) A laser pulse pair separated in space and at a fixed delay acts as a velocity selecting detector, while the timing of the incident pulsed molecular beam is scanned. (right panel) The two-laser signal intensity versus delay with respect to the pulsed molecular beam. The kinetic trace is biexponential reflecting CO desorption from terraces and steps. Velocity resolved kinetics turned out to provide site specific kinetics in almost every system we studied. Figure reprinted with permission from ref (96). Copyright 2015 American Chemical Society. Figure 11. The first velocity resolved kinetics experiment using ion imaging. The inset labeled Pt(111) shows an ion image with velocity-space integration windows for the hyperthermal (red) and the thermal (blue) channels. The dashed black line represents the measured CO dosing function; the onset of the incident CO beam is taken as the zero of time. The solid red and blue lines are fits resulting from a kinetic model involving three reactions. The two traces accurately reflect the branching ratio (8.6:1 in favor of the thermal channel). Note that for the reaction on the (332) sample, the hyperthermal channel is absent. This shows that the hyperthermal reaction takes place at terraces. Figure reprinted with permission from ref (97). Copyright 2018 Macmillan Publishers Ltd., part of Springer Nature. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.5c01323. 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