1
|
Krajňák V, Wiggins S. Roaming in acetaldehyde. J Chem Phys 2024; 160:244104. [PMID: 38912673 DOI: 10.1063/5.0212443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2024] [Accepted: 05/27/2024] [Indexed: 06/25/2024] Open
Abstract
We investigate roaming in the photodissociation of acetaldehyde (CH3CHO), providing insights into the contrasting roaming dynamics observed for this molecule compared to formaldehyde. We carry out trajectory studies for full-dimensional acetaldehyde, supplemented with an analysis of a two-degree-of-freedom restricted model and obtain evidence for two distinct roaming pathways. Trajectories exhibit roaming at both shorter (9-11.5 au) and larger (14.5-22.9 au) maximum CH3-HCO separations, characterized by differing amounts of HCO rotation. No roaming trajectories were found in the intervening gap region. The roaming dynamics near 14.5-22.9 au are well-reproduced by the restricted model and involve passage through a centrifugal barrier, analogous to formaldehyde roaming. However, the shorter-range 9-11.5 au roaming appears unique to acetaldehyde and is likely facilitated by repulsive interactions absent in the simplified models. Phase space analysis reveals that this additional roaming pathway is inaccessible in the reduced dimensionality system. The findings suggest that acetaldehyde's increased propensity for roaming compared to formaldehyde may arise from the presence of multiple distinct roaming mechanisms rather than solely the higher roaming fragment mass.
Collapse
Affiliation(s)
- Vladimír Krajňák
- School of Mathematics, University of Bristol, Fry Building, Woodland Road, Bristol BS8 1UG, United Kingdom
| | - Stephen Wiggins
- School of Mathematics, University of Bristol, Fry Building, Woodland Road, Bristol BS8 1UG, United Kingdom
- Department of Mathematics, United States Naval Academy, Chauvenet Hall, 572C Holloway Road, Annapolis, Maryland 21402-5002, USA
| |
Collapse
|
2
|
Jeong BG, Choi HW, Song JK, Park SM. Branching ratio in photodissociation of 1-bromo-3-chlorobenzene cation. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022; 271:120899. [PMID: 35104740 DOI: 10.1016/j.saa.2022.120899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 01/06/2022] [Accepted: 01/12/2022] [Indexed: 06/14/2023]
Abstract
A new and convenient calculation method based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory assuming an extremely loose transition state (LTS) has been attempted to predict the branching ratio in photodissociation. This method enables estimation of the branching ratios without detailed structural information on the transition state which is indispensable in conventional RRKM calculations. To evaluate our simple method through comparison to the experimental results, photodissociation of 1-bromo-3-chlorobenzene cation (3BCB+) was chosen as a model unimolecular reaction system which has two distinct photodissociation channels in ultraviolet region: 3BCB+ → Br-dissociated daughter ion (ClBz+) + Br and 3BCB+ → Cl-dissociated daughter ion (BrBz+) + Cl. The branching ratio was monitored with decreasing the internal energy using a linear tandem time-of-flight mass spectrometer, which clearly showed decreased branching ratios of 3BCB+ → ClBz+ + Br over 3BCB+ → BrBz+ + Cl in reasonable agreement with the calculation results employing the new method. Although there was some discrepancy in internal energy between the experimental and calculation results, the new calculation method is worth to be extended to other diverse systems considering its intuitive and simple nature.
Collapse
Affiliation(s)
- Bong Gyu Jeong
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Hyun Wook Choi
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Jae Kyu Song
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea.
| | - Seung Min Park
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea.
| |
Collapse
|
3
|
Krajňák V, Naik S, Wiggins S. Predicting trajectory behaviour via machine-learned invariant manifolds. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2021.139290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
4
|
Nagahata Y, Hernandez R, Komatsuzaki T. Phase space geometry of isolated to condensed chemical reactions. J Chem Phys 2021; 155:210901. [PMID: 34879678 DOI: 10.1063/5.0059618] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The complexity of gas and condensed phase chemical reactions has generally been uncovered either approximately through transition state theories or exactly through (analytic or computational) integration of trajectories. These approaches can be improved by recognizing that the dynamics and associated geometric structures exist in phase space, ensuring that the propagator is symplectic as in velocity-Verlet integrators and by extending the space of dividing surfaces to optimize the rate variationally, respectively. The dividing surface can be analytically or variationally optimized in phase space, not just over configuration space, to obtain more accurate rates. Thus, a phase space perspective is of primary importance in creating a deeper understanding of the geometric structure of chemical reactions. A key contribution from dynamical systems theory is the generalization of the transition state (TS) in terms of the normally hyperbolic invariant manifold (NHIM) whose geometric phase-space structure persists under perturbation. The NHIM can be regarded as an anchor of a dividing surface in phase space and it gives rise to an exact non-recrossing TS theory rate in reactions that are dominated by a single bottleneck. Here, we review recent advances of phase space geometrical structures of particular relevance to chemical reactions in the condensed phase. We also provide conjectures on the promise of these techniques toward the design and control of chemical reactions.
Collapse
Affiliation(s)
- Yutaka Nagahata
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Rigoberto Hernandez
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Tamiki Komatsuzaki
- Research Center of Mathematics for Social Creativity, Research Institute for Electronic Science, Hokkaido University, Kita 20 Nishi 10, Kita-ku, Sapporo 001-0 020, Japan
| |
Collapse
|
5
|
Palazzetti F, Tsai PY. Photodissociation Dynamics of CO-Forming Channels on the Ground-State Surface of Methyl Formate at 248 nm: Direct Dynamics Study and Assessment of Generalized Multicenter Impulsive Models. J Phys Chem A 2021; 125:1198-1220. [PMID: 33507759 DOI: 10.1021/acs.jpca.0c10464] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The photodissociation dynamics of methyl formate in the electronic ground state S0, initiated by a 248 nm-wavelength laser, is studied by direct dynamics simulations. We analyze five channels, where four of them have as products CH3OH + CO, one leading to the formation of three fragments, H2CO + H2 + CO, and a channel characterized by a roaming transition state. The analysis of energy distribution among the degrees of freedom of the product and the comparison with experimental results previously published by other groups provide the ingredients to distinguish the examined dissociation pathways. The interpretation of the results proves that the characterization of dissociation mechanisms must rely on a dynamics approach involving multiple electronic states, including considerations on the features of the S1/S0 conical intersection. Here, we also assess the generalized multicenter impulsive model, GMCIM, that has been designed for dissociation processes with exit barriers, and the energy distribution in the products is predicted on the basis of information from the saddle points and the intrinsic reaction coordinates. Main features, advantages, limits, and future perspectives of the method are reported and discussed.
Collapse
Affiliation(s)
- Federico Palazzetti
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Perugia 06123, Italy
| | - Po-Yu Tsai
- Department of Chemistry, National Chung Hsing University, Taichung 402, Taiwan
| |
Collapse
|
6
|
Quinn MS, Nauta K, Jordan MJT, Bowman JM, Houston PL, Kable SH. Rotational resonances in the H
2
CO roaming reaction are revealed by detailed correlations. Science 2020; 369:1592-1596. [DOI: 10.1126/science.abc4088] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Accepted: 07/19/2020] [Indexed: 11/03/2022]
Affiliation(s)
- Mitchell S. Quinn
- School of Chemistry, University of New South Wales, Kensington, NSW, 2052, Australia
| | - Klaas Nauta
- School of Chemistry, University of New South Wales, Kensington, NSW, 2052, Australia
| | | | - Joel M. Bowman
- Department of Chemistry, Emory University, Atlanta, GA, USA
| | - Paul L. Houston
- Department of Chemistry and Biochemistry, Cornell University, Ithaca, NY, USA
| | - Scott H. Kable
- School of Chemistry, University of New South Wales, Kensington, NSW, 2052, Australia
| |
Collapse
|
7
|
Abstract
Roaming reactions were first clearly identified in photodissociation of formaldehyde 15 years ago, and roaming dynamics are now recognized as a universal aspect of chemical reactivity. These reactions typically involve frustrated near-dissociation of a quasibound system to radical fragments, followed by reorientation at long range and intramolecular abstraction. The consequences can be unexpected formation of molecular products, depletion of the radical pool in chemical systems, and formation of products with unusual internal state distributions. In this review, I examine some current aspects of roaming reactions with an emphasis on experimental results, focusing on possible quantum effects in roaming and roaming dynamics in bimolecular systems. These considerations lead to a more inclusive definition of roaming reactions as those for which key dynamics take place at long range.
Collapse
Affiliation(s)
- Arthur G. Suits
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| |
Collapse
|
8
|
Feldmaier M, Bardakcioglu R, Reiff J, Main J, Hernandez R. Phase-space resolved rates in driven multidimensional chemical reactions. J Chem Phys 2019; 151:244108. [DOI: 10.1063/1.5127539] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Matthias Feldmaier
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Robin Bardakcioglu
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Johannes Reiff
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Jörg Main
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Rigoberto Hernandez
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| |
Collapse
|
9
|
Dörfler AD, Eberle P, Koner D, Tomza M, Meuwly M, Willitsch S. Long-range versus short-range effects in cold molecular ion-neutral collisions. Nat Commun 2019; 10:5429. [PMID: 31780657 PMCID: PMC6882903 DOI: 10.1038/s41467-019-13218-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Accepted: 10/28/2019] [Indexed: 12/27/2022] Open
Abstract
The investigation of cold interactions between ions and neutrals has recently emerged as a new scientific frontier at the interface of physics and chemistry. Here, we report a study of charge-transfer (CT) collisions of Rb atoms with N\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${}_{2}^{+}$$\end{document}2+ and O\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${}_{2}^{+}$$\end{document}2+ ions in the mK regime using a dynamic ion-neutral hybrid trapping experiment. We observe markedly different CT kinetics and dynamics for the different systems and reaction channels studied. While the kinetics in some channels are consistent with classical capture theory, others show distinct non-universal dynamics. The experimental results are interpreted with the help of classical-capture, quasiclassical-trajectory and quantum-scattering calculations using ab-initio potentials for the highly excited molecular states involved. The theoretical analysis reveals an intricate interplay between short- and long-range effects in the different reaction channels which ultimately determines the CT dynamics and rates. Our results illustrate salient mechanisms that determine the efficiency of cold molecular CT reactions. Studies on reactions between cold molecular ions and neutral atoms provide insights into intermolecular interactions. Here the authors explore the kinetics and dynamics of charge-transfer collisions between the cold N\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${}_{2}^{+}$$\end{document}2+ and O\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${}_{2}^{+}$$\end{document}2+ ions and neutral Rb atoms and discuss the role of long- and short-range effects.
Collapse
Affiliation(s)
- Alexander D Dörfler
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland
| | - Pascal Eberle
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland
| | - Debasish Koner
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland
| | - Michał Tomza
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093, Warsaw, Poland.
| | - Markus Meuwly
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland.
| | - Stefan Willitsch
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland.
| |
Collapse
|
10
|
Yoshida D, Takahashi K. Odd–Even Reactivity Variation Due to Dynamical Effects around the Roaming Saddle Points of the Reaction Between C n– Chain ( n = 2–8) and H 2. J Phys Chem A 2019; 123:5300-5308. [DOI: 10.1021/acs.jpca.9b03435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Daisuke Yoshida
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 10617, Republic of China
| | - Kaito Takahashi
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 10617, Republic of China
| |
Collapse
|
11
|
Feldmaier M, Schraft P, Bardakcioglu R, Reiff J, Lober M, Tschöpe M, Junginger A, Main J, Bartsch T, Hernandez R. Invariant Manifolds and Rate Constants in Driven Chemical Reactions. J Phys Chem B 2019; 123:2070-2086. [DOI: 10.1021/acs.jpcb.8b10541] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Matthias Feldmaier
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Philippe Schraft
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Robin Bardakcioglu
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Johannes Reiff
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Melissa Lober
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Martin Tschöpe
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Andrej Junginger
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Jörg Main
- Institut für Theoretische Physik 1, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Thomas Bartsch
- Centre for Nonlinear Mathematics and Applications, Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, United Kingdom
| | - Rigoberto Hernandez
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| |
Collapse
|
12
|
Kapnas KM, McCaslin LM, Murray C. UV photofragmentation dynamics of acetaldehyde cations prepared by single-photon VUV ionization. Phys Chem Chem Phys 2019; 21:14214-14225. [DOI: 10.1039/c8cp06640j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
UV excitation of cold acetaldehyde cations prepared by single-photon VUV ionization results in remarkably rich photochemistry.
Collapse
Affiliation(s)
- Kara M. Kapnas
- Department of Chemistry
- University of California, Irvine
- Irvine
- USA
| | - Laura M. McCaslin
- The Fritz Haber Center and The Institute of Chemistry
- The Hebrew University
- Jerusalem 91904
- Israel
| | - Craig Murray
- Department of Chemistry
- University of California, Irvine
- Irvine
- USA
| |
Collapse
|
13
|
Krajňák V, Wiggins S. Influence of mass and potential energy surface geometry on roaming in Chesnavich's CH4+ model. J Chem Phys 2018; 149:094109. [PMID: 30195292 DOI: 10.1063/1.5044532] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Chesnavich's model Hamiltonian for the reaction CH4+→ CH3+ + H is known to exhibit a range of interesting dynamical phenomena including roaming. The model system consists of two parts: a rigid, symmetric top representing the CH3+ ion and a free H atom. We study roaming in this model with focus on the evolution of geometrical features of the invariant manifolds in phase space that govern roaming under variations of the mass of the free atom m and a parameter a that couples radial and angular motion. In addition, we establish an upper bound on the prominence of roaming in Chesnavich's model. The bound highlights the intricacy of roaming as a type of dynamics on the verge between isomerisation and nonreactivity as it relies on generous access to the potential wells to allow reactions as well as a prominent area of high potential that aids sufficient transfer of energy between the degrees of freedom to prevent isomerisation.
Collapse
Affiliation(s)
- Vladimír Krajňák
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| | - Stephen Wiggins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| |
Collapse
|
14
|
Leitner DM. Molecules and the Eigenstate Thermalization Hypothesis. ENTROPY 2018; 20:e20090673. [PMID: 33265762 PMCID: PMC7513195 DOI: 10.3390/e20090673] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 09/02/2018] [Accepted: 09/03/2018] [Indexed: 11/18/2022]
Abstract
We review a theory that predicts the onset of thermalization in a quantum mechanical coupled non-linear oscillator system, which models the vibrational degrees of freedom of a molecule. A system of N non-linear oscillators perturbed by cubic anharmonic interactions exhibits a many-body localization (MBL) transition in the vibrational state space (VSS) of the molecule. This transition can occur at rather high energy in a sizable molecule because the density of states coupled by cubic anharmonic terms scales as N3, in marked contrast to the total density of states, which scales as exp(aN), where a is a constant. The emergence of a MBL transition in the VSS is seen by analysis of a random matrix ensemble that captures the locality of coupling in the VSS, referred to as local random matrix theory (LRMT). Upon introducing higher order anharmonicity, the location of the MBL transition of even a sizable molecule, such as an organic molecule with tens of atoms, still lies at an energy that may exceed the energy to surmount a barrier to reaction, such as a barrier to conformational change. Illustrative calculations are provided, and some recent work on the influence of thermalization on thermal conduction in molecular junctions is also discussed.
Collapse
Affiliation(s)
- David M Leitner
- Department of Chemistry, University of Nevada, Reno, NV 89557, USA
| |
Collapse
|
15
|
Cofer-Shabica DV, Stratt RM. What is special about how roaming chemical reactions traverse their potential surfaces? Differences in geodesic paths between roaming and non-roaming events. J Chem Phys 2018; 146:214303. [PMID: 28595418 DOI: 10.1063/1.4984617] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
With the notable exception of some illustrative two-degree-of-freedom models whose surprising classical dynamics has been worked out in detail, theories of roaming have largely bypassed the issue of when and why the counterintuitive phenomenon of roaming occurs. We propose that a useful way to begin to address these issues is to look for the geodesic (most efficient) pathways through the potential surfaces of candidate systems. Although roaming manifests itself in an unusual behavior at asymptotic geometries, we found in the case of formaldehyde dissociation that it was the pathways traversing the parts of the potential surface corresponding to highly vibrationally excited reactants that were the most revealing. An examination of the geodesics for roaming pathways in this region finds that they are much less tightly defined than the geodesics in that same region that lead directly to dissociation (whether into closed-shell products or into radical products). Thus, the broader set of options available to the roaming channel gives it an entropic advantage over more conventional reaction channels. These observations suggest that what leads to roaming in other systems may be less the presence of a localized "roaming transition state," than the existence of an entire region of the potential surface conducive to multiple equivalent pathways.
Collapse
Affiliation(s)
| | - Richard M Stratt
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| |
Collapse
|
16
|
Krajňák V, Waalkens H. The phase space geometry underlying roaming reaction dynamics. JOURNAL OF MATHEMATICAL CHEMISTRY 2018; 56:2341-2378. [PMID: 30956381 PMCID: PMC6428411 DOI: 10.1007/s10910-018-0895-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 01/23/2018] [Indexed: 06/09/2023]
Abstract
Recent studies have found an unusual way of dissociation in formaldehyde. It can be characterized by a hydrogen atom that separates from the molecule, but instead of dissociating immediately it roams around the molecule for a considerable amount of time and extracts another hydrogen atom from the molecule prior to dissociation. This phenomenon has been coined roaming and has since been reported in the dissociation of a number of other molecules. In this paper we investigate roaming in Chesnavich's CH 4 + model. During dissociation the free hydrogen must pass through three phase space bottleneck for the classical motion, that can be shown to exist due to unstable periodic orbits. None of these orbits is associated with saddle points of the potential energy surface and hence related to transition states in the usual sense. We explain how the intricate phase space geometry influences the shape and intersections of invariant manifolds that form separatrices, and establish the impact of these phase space structures on residence times and rotation numbers. Ultimately we use this knowledge to attribute the roaming phenomenon to particular heteroclinic intersections.
Collapse
Affiliation(s)
- Vladimír Krajňák
- Johann Bernoulli Institute, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
- Present Address: School of Mathematics, University of Bristol, University Walk, Bristol, BS8 1TW UK
| | - Holger Waalkens
- Johann Bernoulli Institute, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
| |
Collapse
|
17
|
Abstract
The phenomenon of roaming in chemical reactions has now become both commonly observed in experiment and extensively supported by theory and simulations. Roaming occurs in highly-excited molecules when the trajectories of atomic motion often bypass the minimum energy pathway and produce reaction in unexpected ways from unlikely geometries. The prototypical example is the unimolecular dissociation of formaldehyde (H2CO), in which the "normal" reaction proceeds through a tight transition state to yield H2 + CO but for which a high fraction of dissociations take place via a "roaming" mechanism in which one H atom moves far from the HCO, almost to dissociation, and then returns to abstract the second H atom. We review below the theories and simulations that have recently been developed to address and understand this new reaction phenomenon.
Collapse
Affiliation(s)
- Joel M Bowman
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University Atlanta, Georgia 30322, USA.
| | | |
Collapse
|
18
|
Mauguière FA, Collins P, Kramer ZC, Carpenter BK, Ezra GS, Farantos SC, Wiggins S. Roaming: A Phase Space Perspective. Annu Rev Phys Chem 2017; 68:499-524. [DOI: 10.1146/annurev-physchem-052516-050613] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
| | - Peter Collins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom;, ,
| | - Zeb C. Kramer
- Department of Chemistry and Biochemistry, La Salle University, Philadelphia, Pennsylvania 19141
| | - Barry K. Carpenter
- School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom
| | - Gregory S. Ezra
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853
| | - Stavros C. Farantos
- Department of Chemistry, University of Crete, Heraklion 700 13, Greece
- Institute of Electronic Structure and Laser, Foundation for Research and Technology—Hellas, Heraklion 711 10, Greece
| | - Stephen Wiggins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom;, ,
| |
Collapse
|
19
|
Ma X, Hase WL. Perspective: chemical dynamics simulations of non-statistical reaction dynamics. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2017; 375:rsta.2016.0204. [PMID: 28320906 PMCID: PMC5360902 DOI: 10.1098/rsta.2016.0204] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 01/05/2017] [Indexed: 06/06/2023]
Abstract
Non-statistical chemical dynamics are exemplified by disagreements with the transition state (TS), RRKM and phase space theories of chemical kinetics and dynamics. The intrinsic reaction coordinate (IRC) is often used for the former two theories, and non-statistical dynamics arising from non-IRC dynamics are often important. In this perspective, non-statistical dynamics are discussed for chemical reactions, with results primarily obtained from chemical dynamics simulations and to a lesser extent from experiment. The non-statistical dynamical properties discussed are: post-TS dynamics, including potential energy surface bifurcations, product energy partitioning in unimolecular dissociation and avoiding exit-channel potential energy minima; non-RRKM unimolecular decomposition; non-IRC dynamics; direct mechanisms for bimolecular reactions with pre- and/or post-reaction potential energy minima; non-TS theory barrier recrossings; and roaming dynamics.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.
Collapse
Affiliation(s)
- Xinyou Ma
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - William L Hase
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| |
Collapse
|
20
|
Zanchet A, Roncero O, Bulut N. Quantum and quasi-classical calculations for the S⁺ + H₂(v,j) → SH⁺(v',j') + H reactive collisions. Phys Chem Chem Phys 2016; 18:11391-400. [PMID: 27055725 PMCID: PMC4894552 DOI: 10.1039/c6cp00604c] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
State-to-state cross-sections for the S(+) + H2(v,j) → SH(+)(v',j') + H endothermic reaction are obtained using quantum wave packet (WP) and quasi-classical (QCT) methods for different initial ro-vibrational H2(v,j) over a wide range of translation energies. The final state distribution as a function of the initial quantum number is obtained and discussed. Additionally, the effect of the internal excitation of H2 on the reactivity is carefully studied. It appears that energy transfer among modes is very inefficient that vibrational energy is the most favorable for the reaction, and rotational excitation significantly enhances the reactivity when vibrational energy is sufficient to reach the product. Special attention is also paid to an unusual discrepancy between classical and quantum dynamics for low rotational levels while agreement improves with rotational excitation of H2. An interesting resonant behaviour found in WP calculations is also discussed and associated with the existence of roaming classical trajectories that enhance the reactivity of the title reaction. Finally, a comparison with the experimental results of Stowe et al. for S(+) + HD and S(+) + D2 reactions exhibits a reasonably good agreement with those results.
Collapse
Affiliation(s)
- Alexandre Zanchet
- Instituto de Física Fundamental, CSIC, C/Serrano, 123, 28006 Madrid, Spain.
| | - Octavio Roncero
- Instituto de Física Fundamental, CSIC, C/Serrano, 123, 28006 Madrid, Spain.
| | - Niyazi Bulut
- Department of Physics, Firat University, Elazig, Turkey
| |
Collapse
|
21
|
Mauguière FAL, Collins P, Stamatiadis S, Li A, Ezra GS, Farantos SC, Kramer ZC, Carpenter BK, Wiggins S, Guo H. Toward Understanding the Roaming Mechanism in H + MgH → Mg + HH Reaction. J Phys Chem A 2016; 120:5145-54. [PMID: 26918375 DOI: 10.1021/acs.jpca.6b00682] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio three-dimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase space where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. The complex forming trajectories in the HMgH well can either return to the radical channel or "roam" to the MgHH minimum from where the molecule may react.
Collapse
Affiliation(s)
| | - Peter Collins
- School of Mathematics, University of Bristol , Bristol BS8 1TW, United Kingdom
| | - Stamatis Stamatiadis
- Department of Materials Science and Technology, University of Crete , Iraklion 710 03, Greece
| | - Anyang Li
- Department of Chemistry and Chemical Biology, University of New Mexico , Albuquerque, New Mexico 87131, United States
| | - Gregory S Ezra
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States
| | - Stavros C Farantos
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, and Department of Chemistry, University of Crete, Iraklion 711 10, Greece
| | - Zeb C Kramer
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States
| | - Barry K Carpenter
- School of Chemistry, Cardiff University , Cardiff CF10 3AT, United Kingdom
| | - Stephen Wiggins
- School of Mathematics, University of Bristol , Bristol BS8 1TW, United Kingdom
| | - Hua Guo
- Department of Chemistry and Chemical Biology, University of New Mexico , Albuquerque, New Mexico 87131, United States
| |
Collapse
|
22
|
Mauguière FAL, Collins P, Kramer ZC, Carpenter BK, Ezra GS, Farantos SC, Wiggins S. Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone. J Chem Phys 2016; 144:054107. [DOI: 10.1063/1.4940798] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
| | - Peter Collins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| | - Zeb C. Kramer
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
| | - Barry K. Carpenter
- School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom
| | - Gregory S. Ezra
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
| | - Stavros C. Farantos
- Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, and Department of Chemistry, University of Crete, Iraklion 711 10, Crete, Greece
| | - Stephen Wiggins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| |
Collapse
|
23
|
Craven GT, Hernandez R. Deconstructing field-induced ketene isomerization through Lagrangian descriptors. Phys Chem Chem Phys 2016; 18:4008-18. [DOI: 10.1039/c5cp06624g] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Phase space contours (shown in color) constructed using the method of Lagrangian descriptors resolve the separatrices governing state transitions on the reaction-path potential energy surface (shown in white) for field-induced ketene isomerization.
Collapse
Affiliation(s)
- Galen T. Craven
- Center for Computational Molecular Science and Technology
- School of Chemistry and Biochemistry
- Georgia Institute of Technology
- Atlanta
- USA
| | - Rigoberto Hernandez
- Center for Computational Molecular Science and Technology
- School of Chemistry and Biochemistry
- Georgia Institute of Technology
- Atlanta
- USA
| |
Collapse
|
24
|
|
25
|
Mauguière FAL, Collins P, Kramer ZC, Carpenter BK, Ezra GS, Farantos SC, Wiggins S. Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition. J Phys Chem Lett 2015; 6:4123-4128. [PMID: 26499774 DOI: 10.1021/acs.jpclett.5b01930] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We re-examine the prototypical roaming reaction--hydrogen atom roaming in formaldehyde decomposition--from a phase space perspective. Specifically, we address the question "why do trajectories roam, rather than dissociate through the radical channel?" We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs, we show that in the roaming region, there is an unstable periodic orbit whose stable and unstable manifolds define a conduit that both encompasses all roaming trajectories exiting the formaldehyde well and shepherds them toward the H2···CO well.
Collapse
Affiliation(s)
| | - Peter Collins
- School of Mathematics, University of Bristol , Bristol BS8 1TW, United Kingdom
| | - Zeb C Kramer
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University , Ithaca, New York 14853, United States
| | - Barry K Carpenter
- School of Chemistry, Cardiff University , Cardiff CF10 3AT, United Kingdom
| | - Gregory S Ezra
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University , Ithaca, New York 14853, United States
| | - Stavros C Farantos
- Department of Chemistry, University of Crete and Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas , Iraklion 711 10, Crete, Greece
| | - Stephen Wiggins
- School of Mathematics, University of Bristol , Bristol BS8 1TW, United Kingdom
| |
Collapse
|
26
|
Kramer ZC, Carpenter BK, Ezra GS, Wiggins S. Reaction Path Bifurcation in an Electrocyclic Reaction: Ring-Opening of the Cyclopropyl Radical. J Phys Chem A 2015; 119:6611-30. [DOI: 10.1021/acs.jpca.5b02834] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Zeb C. Kramer
- Department
of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853 United States
| | - Barry K. Carpenter
- School
of Chemistry, University of Cardiff, Cardiff CF10 3AT, United Kingdom
| | - Gregory S. Ezra
- Department
of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853 United States
| | - Stephen Wiggins
- School
of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| |
Collapse
|
27
|
Collins P, Kramer ZC, Carpenter BK, Ezra GS, Wiggins S. Nonstatistical dynamics on the caldera. J Chem Phys 2015; 141:034111. [PMID: 25053305 DOI: 10.1063/1.4889780] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We explore both classical and quantum dynamics of a model potential exhibiting a caldera: that is, a shallow potential well with two pairs of symmetry related index one saddles associated with entrance/exit channels. Classical trajectory simulations at several different energies confirm the existence of the "dynamical matching" phenomenon originally proposed by Carpenter, where the momentum direction associated with an incoming trajectory initiated at a high energy saddle point determines to a considerable extent the outcome of the reaction (passage through the diametrically opposing exit channel). By studying a "stretched" version of the caldera model, we have uncovered a generalized dynamical matching: bundles of trajectories can reflect off a hard potential wall so as to end up exiting predominantly through the transition state opposite the reflection point. We also investigate the effects of dissipation on the classical dynamics. In addition to classical trajectory studies, we examine the dynamics of quantum wave packets on the caldera potential (stretched and unstretched). These computations reveal a quantum mechanical analogue of the "dynamical matching" phenomenon, where the initial expectation value of the momentum direction for the wave packet determines the exit channel through which most of the probability density passes to product.
Collapse
Affiliation(s)
- Peter Collins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| | - Zeb C Kramer
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
| | - Barry K Carpenter
- School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom
| | - Gregory S Ezra
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
| | - Stephen Wiggins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| |
Collapse
|
28
|
Mauguière FAL, Collins P, Ezra GS, Farantos SC, Wiggins S. Roaming dynamics in ion-molecule reactions: phase space reaction pathways and geometrical interpretation. J Chem Phys 2015; 140:134112. [PMID: 24712785 DOI: 10.1063/1.4870060] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A model Hamiltonian for the reaction CH4(+) -> CH3(+) + H, parametrized to exhibit either early or late inner transition states, is employed to investigate the dynamical characteristics of the roaming mechanism. Tight/loose transition states and conventional/roaming reaction pathways are identified in terms of time-invariant objects in phase space. These are dividing surfaces associated with normally hyperbolic invariant manifolds (NHIMs). For systems with two degrees of freedom NHIMS are unstable periodic orbits which, in conjunction with their stable and unstable manifolds, unambiguously define the (locally) non-recrossing dividing surfaces assumed in statistical theories of reaction rates. By constructing periodic orbit continuation/bifurcation diagrams for two values of the potential function parameter corresponding to late and early transition states, respectively, and using the total energy as another parameter, we dynamically assign different regions of phase space to reactants and products as well as to conventional and roaming reaction pathways. The classical dynamics of the system are investigated by uniformly sampling trajectory initial conditions on the dividing surfaces. Trajectories are classified into four different categories: direct reactive and non-reactive trajectories, which lead to the formation of molecular and radical products respectively, and roaming reactive and non-reactive orbiting trajectories, which represent alternative pathways to form molecular and radical products. By analysing gap time distributions at several energies, we demonstrate that the phase space structure of the roaming region, which is strongly influenced by nonlinear resonances between the two degrees of freedom, results in nonexponential (nonstatistical) decay.
Collapse
Affiliation(s)
| | - Peter Collins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| | - Gregory S Ezra
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
| | - Stavros C Farantos
- Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, and Department of Chemistry, University of Crete, Iraklion 711 10, Crete, Greece
| | - Stephen Wiggins
- School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom
| |
Collapse
|
29
|
|
30
|
|