A fitting law for rotational transfer rates: An angular momentum model with predictive power

Osborne, Mark A.; McCaffery, A. J.

doi:10.1063/1.467347

Cited by 88 publications

(145 citation statements)

References 19 publications

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“…In light of the number of binary collisions undergone in a typical computational run, this close agreement implies that the underlying collision physics, i.e. the AM model, 13,14 represents the outcomes of individual diatom-diatom collisions with considerable accuracy.…”

supporting

confidence: 48%

“…The system of mechanics used for determining the outcome of individual diatomic-diatomic, or atom-diatomic collisions is the angular momentum (AM) model of collision -induced state change. This fast, accurate, theoretical method was developed by McCaffery and co-workers 13,14 following a series of experiments designed to reveal the motive force for quantum state change in molecular collisions. These experiments, and the conclusions drawn from them, have been described in a recent review.…”

Section: The Computational Modelmentioning

confidence: 99%

“…The result has enhanced insight into the principal energy relaxation mechanisms in the multi-collision regime. The computational/theoretical model used for calculating state-to-state collision-induced transition probabilities in gas ensembles is based on the angular momentum (AM) model 13,14 of collision-induced, state-to-state energy transfer. In this method, in which the principal features were guided by experimental findings, the probability of converting linear-to-angular momentum (rotational and orbital) is calculated directly.…”

Section: Introductionmentioning

confidence: 99%

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Energy transfer in multi-collision environments; an experimental test of theory: LiH (10;2) in H2(0;0)

Shen

Wang

Dai

et al. 2017

The Journal of Chemical Physics

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Abstract.We report separate experimental and theoretical studies that follow the equilibration of highly excited LiH (v=10;J=2) in H2 at 680K. Experiments that follow the time evolution of state-tostate population transfer in multi-collision conditions were carried out by Shen and co-workers at Xinjiang University and East China Institute of Science and Technology with µs resolution. At the same time, theoretical computations on the relaxation of this gas mixture were undertaken by McCaffery and co-workers at Sussex University. Rapid, near-resonant, vibration-vibration energy exchange is a marked feature of the initial relaxation process. However, at later stages of ensemble evolution, slower vibration-rotation transfer processes form the dominant relaxation mechanism. The physics of the decay process are complex and, as demonstrated experimentally here, a single exponential expression is unlikely to capture the form of this decay with any accuracy. When these separate studies were complete, the evolution of modal temperatures from the Sussex calculations were compared with experimental measurements of these same quantities from Shanghai and Urumqui. The two sets of data were found to be identical to within experimental and computational error. This constitutes an important experimental validation of the theoretical/computational model developed by the Sussex group and a significant experimental advance by the group of Shen et.al.

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supporting

confidence: 48%

Section: The Computational Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Energy transfer in multi-collision environments; an experimental test of theory: LiH (10;2) in H2(0;0)

Shen

Wang

Dai

et al. 2017

The Journal of Chemical Physics

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“…The probability of rotational state change falls rapidly with the magnitude of ⌬J, 18,19 an effect that may be masked by energy constraints. In the absence of specific constraints, transitions are most probable for lowest ⌬J and largest b n max .…”

Section: A Monatomic Collision Partnersmentioning

confidence: 99%

“…b n max is found from experiment to be half the bond length in a homonuclear diatomic molecule 17,18 and an equivalent distance from the center-of-mass in a heteronuclear species. For J-changing collisions of benzene, the torque arm is initially assumed to be the distance from the molecule's center-of-mass to the H atoms.…”

Section: Qualitative Analysis Of 6 1 \0 0 Vibrational Relaxation mentioning

confidence: 99%

The role of angular momentum in collision-induced vibration–rotation relaxation in polyatomics

McCaffery

Osborne

Marsh

et al. 2004

The Journal of Chemical Physics

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Vibrational relaxation of the 6 1 level of S 1 ( 1 B 2u ) benzene is analyzed using the angular momentum model of inelastic processes. Momentum-͑rotational͒ angular momentum diagrams illustrate energetic and angular momentum constraints on the disposal of released energy and the effect of collision partner on resultant benzene rotational excitation. A kinematic ''equivalent rotor'' model is introduced that allows quantitative prediction of rotational distributions from inelastic collisions in polyatomic molecules. The method was tested by predicting K-state distributions in glyoxal-Ne as well as J-state distributions in rotationally inelastic acetylene-He collisions before being used to predict J and K distributions from vibrational relaxation of 6 1 benzene by H 2 , D 2 , and CH 4 . Diagrammatic methods and calculations illustrate changes resulting from simultaneous collision partner excitation, a particularly effective mechanism in p-H 2 where some 70% of the available 6 1 →0 0 energy may be disposed into 0→2 rotation. These results support the explanation for branching ratios in 6 1 →0 0 relaxation given by Waclawik and Lawrance and the absence of this pathway for monatomic partners. Collision-induced vibrational relaxation in molecules represents competition between the magnitude of the energy gap of a potential transition and the ability of the colliding species to generate the angular momentum ͑rotational and orbital͒ needed for the transition to proceed. Transition probability falls rapidly as ⌬J increases and for a given molecule-collision partner pair will provide a limit to the gap that may be bridged. Energy constraints increase as collision partner mass increases, an effect that is amplified when J i Ͼ0. Large energy gaps are most effectively bridged using light collision partners. For efficient vibrational relaxation in polyatomics an additional requirement is that the molecular motion of the mode must be capable of generating molecular rotation on contact with the collision partner in order to meet the angular momentum requirements. We postulate that this may account for some of the striking propensities that characterize polyatomic energy transfer.

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From Ligand Field Theory to Molecular Collision Dynamics: A Common Thread of Angular Momentum

McCaffery

2011

Structure and Bonding

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Interest in, and appreciation of, the role played by angular momentum in chemical physics was first aroused by a Carl Ballhausen lecture early in the author's scientific career. Later came deeper understanding of the fundamental nature of angular momentum and the power of its formal algebraic expression. Spectroscopy using light of precisely defined energy and (z-component of) angular momentum represents a unique experimental probe with the potential to reveal the underlying physics of chemical processes. Experiments using circularly polarised emission of gas phase molecules led to new insights in the field of molecular collision dynamics. Further work, and that of others, suggested an alternative formulation of the mechanics of bimolecular collisions. A theoretical model was developed guided throughout by experiment. Its basis is linear-to-angular momentum conversion within the constraint of state-to-state energy conservation. An evolutionary process guided by experiment is described, with illustrations that demonstrate the power of the angular momentum theory of molecular collisions developed by the author and co-workers. Examples include very recent work on multicollision models of gas ensembles of potential value in, e.g., modelling planetary atmospheres.

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A fitting law for rotational transfer rates: An angular momentum model with predictive power

Cited by 88 publications

References 19 publications

Energy transfer in multi-collision environments; an experimental test of theory: LiH (10;2) in H2(0;0)

Energy transfer in multi-collision environments; an experimental test of theory: LiH (10;2) in H2(0;0)

The role of angular momentum in collision-induced vibration–rotation relaxation in polyatomics

From Ligand Field Theory to Molecular Collision Dynamics: A Common Thread of Angular Momentum

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