A new approach to molecular collision dynamics

McCaffery, A. J.

doi:10.1039/b316161g

Cited by 56 publications

(90 citation statements)

References 98 publications

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“…Parmenter and co-workers, 16 in a series of crossed beam experiments, convincingly demonstrated the central role played by kinematic factors in RT and VRT involving glyoxal. These results suggest that the AM model of inelastic processes, 7,8 developed initially for diatomics, might be useful in the analysis of collision-induced transfer in larger molecules. The approach has both qualitative and quantitative elements.…”

Section: Introductionmentioning

confidence: 94%

“…A full description of the construction and use of these figures is contained in recent reviews. 7,8 This representation displays energy and AM conservation relations for each transition from initial to final ͉v,J͘ states. The figures thus make clear the nature of the constraints that operate on each transition.…”

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

confidence: 99%

“…Molecular rotational AM appears to play a central role in most forms of energy exchange involving diatomic molecules. 7,8 A simple, effective approach to predicting the state-to-state outcome of collisions consists of direct calculation of the probability of linear-to͑rotational͒ angular momentum conversion ͑orbital-torotational in the case of reactive collisions͒. 7,8 We explore this proposal here in the context of polyatomic collisions with particular reference to 6 1 →0 0 transfer in benzene.…”

Section: Introductionmentioning

confidence: 99%

“…14 Direct calculation of the probability of linear-to-angular momentum conversion is fast and yields accurate results. 7,8 Extension to the polyatomic case however is quite challenging. Rotation may occur about more than one molecular axis and collisions cause transitions within or between the discrete energy levels that arise from rotations about these axes.…”

Section: Introductionmentioning

confidence: 99%

“…7,8 Extending this approach to polyatomics represents a challenge due to the complexity of rotational motion in species containing more than one inertial axis. In the general case collisions involving a symmetric rotor change both J and K quantum numbers.…”

Section: Quantitative Analysis; An Equivalent Rotor Modelmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 94%

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

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Quantitative Analysis; An Equivalent Rotor Modelmentioning

confidence: 99%

See 3 more Smart Citations

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 and Rotational Relaxation

Energy Dissipation in Molecular Systems

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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 new approach to molecular collision dynamics

Cited by 56 publications

References 98 publications

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

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

Vibrational and Rotational Relaxation

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

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