Pub Date : 2015-05-21DOI: 10.1080/0144235X.2015.1077838
Yuan-Pin Chang, D. Horke, S. Trippel, J. Küpper
The understanding of molecular structure and function is at the very heart of the chemical and molecular sciences. Experiments that allow for the creation of structurally pure samples and the investigation of their molecular dynamics and chemical function have developed tremendeously over the last few decades, although ‘there’s plenty of room at the bottom’ for better control as well as further applications. Here, we describe the use of inhomogeneous electric fields for the manipulation of neutral molecules in the gas-phase, i.e. for the separation of complex molecules according to size, structural isomer, and quantum state. For these complex molecules, all quantum states are strong-field seeking, requiring dynamic fields for their confinement. Current applications of these controlled samples are summarised and interesting future applications discussed.
{"title":"Spatially-controlled complex molecules and their applications","authors":"Yuan-Pin Chang, D. Horke, S. Trippel, J. Küpper","doi":"10.1080/0144235X.2015.1077838","DOIUrl":"https://doi.org/10.1080/0144235X.2015.1077838","url":null,"abstract":"The understanding of molecular structure and function is at the very heart of the chemical and molecular sciences. Experiments that allow for the creation of structurally pure samples and the investigation of their molecular dynamics and chemical function have developed tremendeously over the last few decades, although ‘there’s plenty of room at the bottom’ for better control as well as further applications. Here, we describe the use of inhomogeneous electric fields for the manipulation of neutral molecules in the gas-phase, i.e. for the separation of complex molecules according to size, structural isomer, and quantum state. For these complex molecules, all quantum states are strong-field seeking, requiring dynamic fields for their confinement. Current applications of these controlled samples are summarised and interesting future applications discussed.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86110190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-03DOI: 10.1080/0144235X.2015.1046679
H. Linnartz, S. Ioppolo, G. Fedoseev
It was in ‘The Magellanic Cloud’ (1955) – a science fiction novel by Stanislaw Lem – that engineers travelling to another star noticed that their spacecraft for unknown reasons overheated. The cause had to be outside the spaceship, but obviously there was only emptiness, at least compared to terrestrial conditions. The space between the stars, the interstellar medium (ISM), however, is not completely empty and at the high speed of the spacecraft the cross-section with impacting particles, even from such a dilute environment, was found to be sufficient to cause an overheating. Today, 60 years later, the ISM has been studied in detail by astronomical observations, reproduced in dedicated laboratory experiments and simulated by complex astrochemical models. The space between the stars is, indeed, far from empty; it comprises gas, dust and ice and the molecules detected so far are both small (diatomics) and large (long carbon chains, PAHs and fullerenes), stable and reactive (radicals, ions, and excited molecules) evidencing an exotic and fascinating chemistry, taking place at low densities, low temperatures and experiencing intense radiation fields. Astrochemists explain the observed chemical complexity in space – so far 185 different molecules (not including isotopologues) have been identified – as the cumulative outcome of reactions in the gas phase and on icy dust grains. Gas phase models explain the observed abundances of a substantial part of the observed species, but fail to explain the number densities for stable molecules, as simple as water, methanol or acetonitrile – one of the most promising precursor species for the simplest amino acid glycine – as well as larger compounds such as glycolaldehyde, dimethylether and ethylene glycol. Evidence has been found that these and other complex species, including organic ones, form on icy dust grains that act as catalytic sites for molecule formation. It is here where particles ‘accrete, meet, and greet’ (i.e. freeze out, diffuse and react) upon energetic and non-energetic processing, such as irradiation by vacuum UV light, interaction with impacting particles (atoms, electrons and cosmic rays) or heating. This review paper summarises the state-of-the-art in laboratory based interstellar ice chemistry. The focus is on atom addition reactions, illustrating how water, carbon dioxide and methanol can form in the solid state at astronomically relevant temperatures, and also the formation of more complex species such as hydroxylamine, an important prebiotic molecule, and glycolaldehyde, the smallest sugar, is discussed. These reactions are particularly relevant during the ‘dark’ ages of star and planet formation, i.e. when the role of UV light is restricted. A quantitative characterization of such processes is only possible through dedicated laboratory studies, i.e. under full control of a large set of parameters such as temperature, atom-flux, and ice morphology. The resulting numbers, physical and chem
{"title":"Atom addition reactions in interstellar ice analogues","authors":"H. Linnartz, S. Ioppolo, G. Fedoseev","doi":"10.1080/0144235X.2015.1046679","DOIUrl":"https://doi.org/10.1080/0144235X.2015.1046679","url":null,"abstract":"It was in ‘The Magellanic Cloud’ (1955) – a science fiction novel by Stanislaw Lem – that engineers travelling to another star noticed that their spacecraft for unknown reasons overheated. The cause had to be outside the spaceship, but obviously there was only emptiness, at least compared to terrestrial conditions. The space between the stars, the interstellar medium (ISM), however, is not completely empty and at the high speed of the spacecraft the cross-section with impacting particles, even from such a dilute environment, was found to be sufficient to cause an overheating. Today, 60 years later, the ISM has been studied in detail by astronomical observations, reproduced in dedicated laboratory experiments and simulated by complex astrochemical models. The space between the stars is, indeed, far from empty; it comprises gas, dust and ice and the molecules detected so far are both small (diatomics) and large (long carbon chains, PAHs and fullerenes), stable and reactive (radicals, ions, and excited molecules) evidencing an exotic and fascinating chemistry, taking place at low densities, low temperatures and experiencing intense radiation fields. Astrochemists explain the observed chemical complexity in space – so far 185 different molecules (not including isotopologues) have been identified – as the cumulative outcome of reactions in the gas phase and on icy dust grains. Gas phase models explain the observed abundances of a substantial part of the observed species, but fail to explain the number densities for stable molecules, as simple as water, methanol or acetonitrile – one of the most promising precursor species for the simplest amino acid glycine – as well as larger compounds such as glycolaldehyde, dimethylether and ethylene glycol. Evidence has been found that these and other complex species, including organic ones, form on icy dust grains that act as catalytic sites for molecule formation. It is here where particles ‘accrete, meet, and greet’ (i.e. freeze out, diffuse and react) upon energetic and non-energetic processing, such as irradiation by vacuum UV light, interaction with impacting particles (atoms, electrons and cosmic rays) or heating. This review paper summarises the state-of-the-art in laboratory based interstellar ice chemistry. The focus is on atom addition reactions, illustrating how water, carbon dioxide and methanol can form in the solid state at astronomically relevant temperatures, and also the formation of more complex species such as hydroxylamine, an important prebiotic molecule, and glycolaldehyde, the smallest sugar, is discussed. These reactions are particularly relevant during the ‘dark’ ages of star and planet formation, i.e. when the role of UV light is restricted. A quantitative characterization of such processes is only possible through dedicated laboratory studies, i.e. under full control of a large set of parameters such as temperature, atom-flux, and ice morphology. The resulting numbers, physical and chem","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77382803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-03DOI: 10.1080/0144235X.2015.1039293
P. Casavecchia, F. Leonori, N. Balucani
We review the progress made in the understanding of the dynamics of the reactions of ground state oxygen atoms, O(3P), with unsaturated hydrocarbons (acetylene, ethylene, allene, propyne and propene) which are of great relevance, besides from a fundamental point of view, in combustion chemistry and of interest also in atmosphere- and astro-chemistry. Advances in this area have been made possible by an improved crossed molecular beams (CMBs) instrument with rotating mass spectrometric detection and time-of-flight analysis which features product detection by low-energy electron soft-ionisation for increased sensitivity and universal detection power. This apparatus offers the capability of identifying virtually all primary reaction channels, characterising the dynamics, and determining the branching ratios (BRs) for these polyatomic multichannel nonadiabatic reactions. The reactive scattering results are rationalised with the assistance of theoretical information from other laboratories on the stationary points and product energetics of the relevant ab initio potential energy surfaces (PESs). For the simpler prototypical systems, such as O(3P) + ethylene, detailed comparisons with synergic state-of-the-art quasiclassical trajectory surface-hopping calculations on full dimensional ab initio coupled triplet and singlet PESs have recently been possible. For more complex systems, such as O(3P) + propene, comparisons with the results of synergic statistical calculations of BRs on ab initio coupled triplet and singlet PESs, have also been carried out very recently. The combined experimental/theoretical approach has allowed for a better understanding of the mechanism of these reactions. And overall has deepened considerably our understanding of chemical reactivity; in addition, these studies provide an important bridge between CMBs dynamics and thermal kinetics as well as valuable information for improving combustion and astrochemistry models.
{"title":"Reaction dynamics of oxygen atoms with unsaturated hydrocarbons from crossed molecular beam studies: primary products, branching ratios and role of intersystem crossing","authors":"P. Casavecchia, F. Leonori, N. Balucani","doi":"10.1080/0144235X.2015.1039293","DOIUrl":"https://doi.org/10.1080/0144235X.2015.1039293","url":null,"abstract":"We review the progress made in the understanding of the dynamics of the reactions of ground state oxygen atoms, O(3P), with unsaturated hydrocarbons (acetylene, ethylene, allene, propyne and propene) which are of great relevance, besides from a fundamental point of view, in combustion chemistry and of interest also in atmosphere- and astro-chemistry. Advances in this area have been made possible by an improved crossed molecular beams (CMBs) instrument with rotating mass spectrometric detection and time-of-flight analysis which features product detection by low-energy electron soft-ionisation for increased sensitivity and universal detection power. This apparatus offers the capability of identifying virtually all primary reaction channels, characterising the dynamics, and determining the branching ratios (BRs) for these polyatomic multichannel nonadiabatic reactions. The reactive scattering results are rationalised with the assistance of theoretical information from other laboratories on the stationary points and product energetics of the relevant ab initio potential energy surfaces (PESs). For the simpler prototypical systems, such as O(3P) + ethylene, detailed comparisons with synergic state-of-the-art quasiclassical trajectory surface-hopping calculations on full dimensional ab initio coupled triplet and singlet PESs have recently been possible. For more complex systems, such as O(3P) + propene, comparisons with the results of synergic statistical calculations of BRs on ab initio coupled triplet and singlet PESs, have also been carried out very recently. The combined experimental/theoretical approach has allowed for a better understanding of the mechanism of these reactions. And overall has deepened considerably our understanding of chemical reactivity; in addition, these studies provide an important bridge between CMBs dynamics and thermal kinetics as well as valuable information for improving combustion and astrochemistry models.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78704312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-03DOI: 10.1080/0144235X.2015.1051353
M. Ziemkiewicz, D. Neumark, O. Gessner
Helium nanodroplets have emerged as a test bed for the study of isolated quantum liquids and as an ideal matrix for trapping atoms and molecules in a weakly interacting, cryogenic environment. Their high transparency at visible and infrared wavelengths facilitates the study of dissolved species with traditional spectroscopy techniques. At photon energies above ~21 eV, however, the droplets themselves begin to absorb to form complex excited states that have proven a challenge for both experiment and theory. A variety of frequency- and time-domain methods have been used to characterise electronically excited droplet states and their relaxation channels. This review focuses on a recent series of time-domain experimental studies that have revealed several phenomena such as interband relaxation dynamics within the droplet environment, and provided deeper insight into previously detected relaxation channels, including the ejection of Rydberg atoms (He*) and molecules (), the dynamics of highly excited droplet states, and photoassociation to produce strongly-bound excimer species (such as ). A brief outline of corresponding ab initio efforts for the theoretical description of electronically excited He droplet states and their relaxation dynamics will also be given.
{"title":"Ultrafast electronic dynamics in helium nanodroplets","authors":"M. Ziemkiewicz, D. Neumark, O. Gessner","doi":"10.1080/0144235X.2015.1051353","DOIUrl":"https://doi.org/10.1080/0144235X.2015.1051353","url":null,"abstract":"Helium nanodroplets have emerged as a test bed for the study of isolated quantum liquids and as an ideal matrix for trapping atoms and molecules in a weakly interacting, cryogenic environment. Their high transparency at visible and infrared wavelengths facilitates the study of dissolved species with traditional spectroscopy techniques. At photon energies above ~21 eV, however, the droplets themselves begin to absorb to form complex excited states that have proven a challenge for both experiment and theory. A variety of frequency- and time-domain methods have been used to characterise electronically excited droplet states and their relaxation channels. This review focuses on a recent series of time-domain experimental studies that have revealed several phenomena such as interband relaxation dynamics within the droplet environment, and provided deeper insight into previously detected relaxation channels, including the ejection of Rydberg atoms (He*) and molecules (), the dynamics of highly excited droplet states, and photoassociation to produce strongly-bound excimer species (such as ). A brief outline of corresponding ab initio efforts for the theoretical description of electronically excited He droplet states and their relaxation dynamics will also be given.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73250607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-03DOI: 10.1080/0144235X.2015.1051354
Gareth W Richings, I. Polyak, K. E. Spinlove, Graham A Worth, I. Burghardt, B. Lasorne
Gaussian wavepacket methods are an attractive way to solve the time-dependent Schrödinger equation (TDSE). They have an underlying trajectory picture that has a natural connection to semi-classical mechanics, allowing a simple pictorial interpretation of an evolving wavepacket. They also have better scaling with system size compared to conventional grid-based techniques. Here we review the variational multi-configurational Gaussian (vMCG) method. This is a variational solution to the TDSE, with explicit coupling between the Gaussian basis functions, resulting in a favourable convergence on the exact solution. The implementation of the method and its performance will be discussed with examples from non-adiabatic photo-excited dynamics and tunneling to show that it can correctly describe both of these strongly quantum mechanical processes. Particular emphasis is given to the implementation of the direct dynamics variant, DD-vMCG, where the potential surfaces are calculated on-the-fly via an interface to quantum chemistry programs.
{"title":"Quantum dynamics simulations using Gaussian wavepackets: the vMCG method","authors":"Gareth W Richings, I. Polyak, K. E. Spinlove, Graham A Worth, I. Burghardt, B. Lasorne","doi":"10.1080/0144235X.2015.1051354","DOIUrl":"https://doi.org/10.1080/0144235X.2015.1051354","url":null,"abstract":"Gaussian wavepacket methods are an attractive way to solve the time-dependent Schrödinger equation (TDSE). They have an underlying trajectory picture that has a natural connection to semi-classical mechanics, allowing a simple pictorial interpretation of an evolving wavepacket. They also have better scaling with system size compared to conventional grid-based techniques. Here we review the variational multi-configurational Gaussian (vMCG) method. This is a variational solution to the TDSE, with explicit coupling between the Gaussian basis functions, resulting in a favourable convergence on the exact solution. The implementation of the method and its performance will be discussed with examples from non-adiabatic photo-excited dynamics and tunneling to show that it can correctly describe both of these strongly quantum mechanical processes. Particular emphasis is given to the implementation of the direct dynamics variant, DD-vMCG, where the potential surfaces are calculated on-the-fly via an interface to quantum chemistry programs.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75098135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-01-02DOI: 10.1080/0144235X.2014.988038
S. Auerbach, W. Fan, P. A. Monson
We present a perspective on the molecular modelling of nanoporous silica material synthesis. We focus on two classes of materials: microporous zeolite materials in their all-silica forms, and ordered mesoporous silica materials. Several approaches have provided insight into the synthesis processes. These approaches range from quantum chemistry modelling of silica polymerisation to molecular simulations of ordered mesoporous silica assembly, and consider physical and chemical phenomena over several lengths and time scales. Our article focuses on models of porous silica material formation based on the assembly of corner-sharing tetrahedra, which we illustrate with applications to silica polymerisation, the formation of microporous crystals and the formation of ordered mesoporous materials. This is a research area where theoretical developments must closely align with experimentation. For this reason, we also devote a significant component of the present review to a survey of key developments in the experimental synthesis and characterisation of these materials. In particular, recent experiments have bracketed length scales of zeolite nuclei in the 5–10 nm range. On the other hand, recent molecular modelling work has accomplished the in silico self-assembly of both zeolitic and mesoporous materials within a unified modelling format. Our article serves to demonstrate the substantial progress that has been made in this field, while highlighting the enormous challenges and opportunities for future progress, such as in understanding the interplay of thermodynamics and kinetics in silica nanopore formation.
{"title":"Modelling the assembly of nanoporous silica materials","authors":"S. Auerbach, W. Fan, P. A. Monson","doi":"10.1080/0144235X.2014.988038","DOIUrl":"https://doi.org/10.1080/0144235X.2014.988038","url":null,"abstract":"We present a perspective on the molecular modelling of nanoporous silica material synthesis. We focus on two classes of materials: microporous zeolite materials in their all-silica forms, and ordered mesoporous silica materials. Several approaches have provided insight into the synthesis processes. These approaches range from quantum chemistry modelling of silica polymerisation to molecular simulations of ordered mesoporous silica assembly, and consider physical and chemical phenomena over several lengths and time scales. Our article focuses on models of porous silica material formation based on the assembly of corner-sharing tetrahedra, which we illustrate with applications to silica polymerisation, the formation of microporous crystals and the formation of ordered mesoporous materials. This is a research area where theoretical developments must closely align with experimentation. For this reason, we also devote a significant component of the present review to a survey of key developments in the experimental synthesis and characterisation of these materials. In particular, recent experiments have bracketed length scales of zeolite nuclei in the 5–10 nm range. On the other hand, recent molecular modelling work has accomplished the in silico self-assembly of both zeolitic and mesoporous materials within a unified modelling format. Our article serves to demonstrate the substantial progress that has been made in this field, while highlighting the enormous challenges and opportunities for future progress, such as in understanding the interplay of thermodynamics and kinetics in silica nanopore formation.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90340467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-01-02DOI: 10.1080/0144235X.2015.1022946
Himansu S. Biswal, Surjendu Bhattacharyya, Aditi Bhattacherjee, S. Wategaonkar
The importance of Sulfur centred hydrogen bonds (SCHBs) cannot be underestimated given the current day knowledge of its non-covalent interactions prevalent in many biopolymers as well as in organic systems. Based on the distance/angle constraints available from the structural database, these interactions have been interchangeably termed as van der Waals/hydrogen bonded complexes. There is a lack of sufficient spectroscopic evidence that can unequivocally term these interactions as hydrogen bonding interactions. In this review we present laser spectroscopic investigations of isolated binary complexes of H-bond donor-acceptor molecules containing Sulfur atom. The complexes were formed using supersonic jet expansion method and the IR/UV spectroscopic investigations were carried out on mass selected binary complexes. The pertinent questions regarding SCHBs addressed herein are (1) Is electronegativity the controlling factor to be a potent H-bond donor/acceptor? (2) How do SCHBs compare with their oxygen counterpart? (3) What is the nature of SCHBs, i.e. what are the dominating forces in stabilising these hydrogen bonds? (4) Do SCHBs follow classical H-bond acid–base formalism? (5) Are SCHBs found in peptides and proteins? If so, what are their strengths? Do they control the structure of the peptides? The experimental investigations were also supported by high level of ab initio computations.
{"title":"Nature and strength of sulfur-centred hydrogen bonds: laser spectroscopic investigations in the gas phase and quantum-chemical calculations","authors":"Himansu S. Biswal, Surjendu Bhattacharyya, Aditi Bhattacherjee, S. Wategaonkar","doi":"10.1080/0144235X.2015.1022946","DOIUrl":"https://doi.org/10.1080/0144235X.2015.1022946","url":null,"abstract":"The importance of Sulfur centred hydrogen bonds (SCHBs) cannot be underestimated given the current day knowledge of its non-covalent interactions prevalent in many biopolymers as well as in organic systems. Based on the distance/angle constraints available from the structural database, these interactions have been interchangeably termed as van der Waals/hydrogen bonded complexes. There is a lack of sufficient spectroscopic evidence that can unequivocally term these interactions as hydrogen bonding interactions. In this review we present laser spectroscopic investigations of isolated binary complexes of H-bond donor-acceptor molecules containing Sulfur atom. The complexes were formed using supersonic jet expansion method and the IR/UV spectroscopic investigations were carried out on mass selected binary complexes. The pertinent questions regarding SCHBs addressed herein are (1) Is electronegativity the controlling factor to be a potent H-bond donor/acceptor? (2) How do SCHBs compare with their oxygen counterpart? (3) What is the nature of SCHBs, i.e. what are the dominating forces in stabilising these hydrogen bonds? (4) Do SCHBs follow classical H-bond acid–base formalism? (5) Are SCHBs found in peptides and proteins? If so, what are their strengths? Do they control the structure of the peptides? The experimental investigations were also supported by high level of ab initio computations.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85119343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-01-02DOI: 10.1080/0144235X.2014.1001220
M. Hermes, S. Hirata
In this review, we summarise recent developments in our laboratory in the field of many-body quantum-mechanical calculations of the anharmonic vibrational structure of molecules. Our size-extensive vibrational self-consistent field (XVSCF) and size-extensive second-order many-body perturbation (XVMP2) methods are, unlike their parent methods (VSCF and VMP2), defined in diagrammatic formulations of the energies and Dyson self-energies, leading to manifestly size-consistent expressions for zero-point energies and anharmonic vibrational frequencies calculable with much greater efficiency. The effective one-mode potentials of XVSCF are quadratic and hence the Schrödinger equation for each mode can be solved analytically, unlike VSCF, where a basis-set expansion of wave functions on more complex one-mode potentials need to be performed; VSCF potentials and their minima (anharmonic geometry) are shown to reduce to the quadratic potentials and their minima (also given analytically) of XVSCF in the thermodynamic limit. By self-consistently solving the Dyson equation with frequency-dependent self-energies, XVMP2 has the ability to calculate anharmonic frequencies of fundamentals as well as combinations and overtones in the presence of strong anharmonic resonance without a multireference or quasi-degenerate formulation, which tends to be non-size-consistent. To eliminate the computational bottleneck of XVSCF and XVMP2, which is the high-rank force-constant evaluation, we have developed alternative algorithms in which the diagrammatic equations are recast as a small number of high-dimensional integrals and then evaluated stochastically using a Metropolis Monte Carlo (MC) method. These MC-XVSCF and MC-XVMP2 methods not only remove the need for force-constant evaluation or storage, but also take into account force constants of up to infinite order according to their importance. They are a new branch of quantum Monte Carlo which can calculate frequencies (excitation energies) directly without fixed-node errors.
{"title":"Diagrammatic theories of anharmonic molecular vibrations","authors":"M. Hermes, S. Hirata","doi":"10.1080/0144235X.2014.1001220","DOIUrl":"https://doi.org/10.1080/0144235X.2014.1001220","url":null,"abstract":"In this review, we summarise recent developments in our laboratory in the field of many-body quantum-mechanical calculations of the anharmonic vibrational structure of molecules. Our size-extensive vibrational self-consistent field (XVSCF) and size-extensive second-order many-body perturbation (XVMP2) methods are, unlike their parent methods (VSCF and VMP2), defined in diagrammatic formulations of the energies and Dyson self-energies, leading to manifestly size-consistent expressions for zero-point energies and anharmonic vibrational frequencies calculable with much greater efficiency. The effective one-mode potentials of XVSCF are quadratic and hence the Schrödinger equation for each mode can be solved analytically, unlike VSCF, where a basis-set expansion of wave functions on more complex one-mode potentials need to be performed; VSCF potentials and their minima (anharmonic geometry) are shown to reduce to the quadratic potentials and their minima (also given analytically) of XVSCF in the thermodynamic limit. By self-consistently solving the Dyson equation with frequency-dependent self-energies, XVMP2 has the ability to calculate anharmonic frequencies of fundamentals as well as combinations and overtones in the presence of strong anharmonic resonance without a multireference or quasi-degenerate formulation, which tends to be non-size-consistent. To eliminate the computational bottleneck of XVSCF and XVMP2, which is the high-rank force-constant evaluation, we have developed alternative algorithms in which the diagrammatic equations are recast as a small number of high-dimensional integrals and then evaluated stochastically using a Metropolis Monte Carlo (MC) method. These MC-XVSCF and MC-XVMP2 methods not only remove the need for force-constant evaluation or storage, but also take into account force constants of up to infinite order according to their importance. They are a new branch of quantum Monte Carlo which can calculate frequencies (excitation energies) directly without fixed-node errors.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81903702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-01-02DOI: 10.1080/0144235X.2014.979659
N. Heine, K. Asmis
Recent advances in the gas phase vibrational spectroscopy of mass-selected ions are described, highlighting experiments on hydrogen-bonded (HBed) clusters relevant to atmospheric chemistry. The use of cryogenic ion traps in combination with the widely tunable and intense radiation from infrared free electron lasers has allowed for new molecular-level insights into the structure and other properties of HBed clusters. Advances and challenges in the interpretation of their vibrational action spectra, in particular, the importance of considering anharmonic effects, are described and discussed. The advantages of isomer-specific measurements relying exclusively on excitations within the vibrational manifold are also evaluated. The article concludes with an outlook on future challenges and perspectives.
{"title":"Cryogenic ion trap vibrational spectroscopy of hydrogen-bonded clusters relevant to atmospheric chemistry","authors":"N. Heine, K. Asmis","doi":"10.1080/0144235X.2014.979659","DOIUrl":"https://doi.org/10.1080/0144235X.2014.979659","url":null,"abstract":"Recent advances in the gas phase vibrational spectroscopy of mass-selected ions are described, highlighting experiments on hydrogen-bonded (HBed) clusters relevant to atmospheric chemistry. The use of cryogenic ion traps in combination with the widely tunable and intense radiation from infrared free electron lasers has allowed for new molecular-level insights into the structure and other properties of HBed clusters. Advances and challenges in the interpretation of their vibrational action spectra, in particular, the importance of considering anharmonic effects, are described and discussed. The advantages of isomer-specific measurements relying exclusively on excitations within the vibrational manifold are also evaluated. The article concludes with an outlook on future challenges and perspectives.","PeriodicalId":54932,"journal":{"name":"International Reviews in Physical Chemistry","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2015-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76592442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-10-02DOI: 10.1080/0144235X.2014.969554
J. M. Weber
The interaction of CO2 with negative charge is of high importance in many natural and industrial processes, since reductive activation is one of the most common and convenient ways to chemically unlock this robust molecule. While free CO2 does not form stable anions, the accessibility of low-lying molecular orbitals is critical for its chemical versatility and allows CO2 to act as solvent as well as a reaction partner for negative ions. Experiments on mass selected cluster ions are highly suitable for the study of the fundamental properties of CO2 and its interaction with excess electrons and anions, since they circumvent many problems associated with experiments in the condensed phase. The combination of mass spectrometry, laser spectroscopy and quantum chemical calculations results in a powerful tool set to address questions of reactivity, ion speciation and solvation, and they can provide key information to understanding the ion chemistry of CO2.
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