A multiple hard-ellipsoid model for rotationally inelastic collisions

Marks, Alison J.

doi:10.1039/ft9949002857

Cited by 28 publications

(25 citation statements)

References 18 publications

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“…For a homonuclear diatomic, the maximum value of this quantity, , is often half the bond length (HBL) though for a heteronuclear species, the identification of is somewhat more complex as we describe below. Quantitative calculations using a hard ellipsoid representation of the potential and Monte Carlo simulation of collision trajectories agree well with experiment . In a number of instances, the maximum value of b n in a homonuclear species is constrained to be less than HBL.…”

Section: Introductionsupporting

confidence: 54%

“…27 Hard ellipsoid Monte Carlo calculations based on LM f AM reproduce RT data quantitatively. 3 The value of a preliminary analysis using the V rel -AM diagrams is that the factors that govern the outcome of collisional phenomena are readily identified. These turn out to be quantities as prosaic (and as readily available) as the energies of the rotational (and for VRT the vibrational) states of the molecule concerned as well as bond length, atomic size and relative velocity.…”

Section: Oh Moleculementioning

confidence: 99%

“…Quantitative calculations using a hard ellipsoid representation of the potential and Monte Carlo simulation of collision trajectories agree well with experiment. 3 In a number of instances, the maximum value of b n in a homonuclear species is constrained to be less than HBL. This is the case in pure RT when initial rotational state N i .…”

Section: Introductionmentioning

confidence: 99%

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Collisional Properties of the OH Molecule

McCaffery

Marsh

2001

J. Phys. Chem. A

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The disposition of the rovibrational levels in a diatomic molecule has a major influence on the outcome of inelastic collisions involving that molecule. In the case of the hydrides of moderately heavy elements, unusual collisional properties are anticipated in view of conflict between the demands of momentum and energy in these species. This arises because hydride rotational and vibrational quanta are generally large yet the species may be quite heavy and thus carry substantial momentum. This leads to competition between the momentum based mechanism for inelastic transfer and constraints which result from energy conservation. We illustrate these principles in investigating rotational, vibration-rotation, and quasiresonant vibration-rotation transfer, as well as vibrational predissociation of OH-containing van der Waals molecules. Collisional transfer is (almost) invariably constrained by energy conservation in this species and the impact of this on the linear-to-angular momentum mechanism is strongly evident in the collisional behavior of the OH molecule. Molecular collision partners may accept vibrational energy from OH without generating angular momentum, resulting in more efficient deactivation of vibrationally excited OH. Recent observation of emission from very high N levels of (X) 2 ΠOH in the nightglow appears to represent only the second recorded example of quasiresonant vibrationrotation transfer.

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Section: Introductionsupporting

confidence: 54%

Section: Oh Moleculementioning

confidence: 99%

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Collisional Properties of the OH Molecule

McCaffery

Marsh

2001

J. Phys. Chem. A

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“…͑2͒ consists in neglecting terms nonlinear in r. We note that the notion of a sharpedged obstacle comes close to the rigid shell approximation. The latter has been widely used in classical, [9][10][11] quantum, 12 and quasi-quantum 13 treatments of field-free molecular collisions, where the collision energy by far exceeds the depth of any potential energy well.…”

Section: Introductionmentioning

confidence: 99%

An analytic model of rotationally inelastic collisions of polar molecules in electric fields

Lemeshko

Friedrich

2008

The Journal of Chemical Physics

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We present an analytic model of thermal state-to-state rotationally inelastic collisions of polar molecules in electric fields. The model is based on the Fraunhofer scattering of matter waves and requires Legendre moments characterizing the "shape" of the target in the body-fixed frame as its input. The electric field orients the target in the space-fixed frame and thereby effects a striking alteration of the dynamical observables: both the phase and amplitude of the oscillations in the partial differential cross sections undergo characteristic field-dependent changes that transgress into the partial integral cross sections. As the cross sections can be evaluated for a field applied parallel or perpendicular to the relative velocity, the model also offers predictions about steric asymmetry.We exemplify the field-dependent quantum collision dynamics with the behavior of the Ne-OCS( 1 Σ) and Ar-NO( 2 Π) systems. A comparison with the close-coupling calculations available for the latter system [Chem. Phys. Lett. 313, 491 (1999)] demonstrates the model's ability to qualitatively explain the field dependence of all the scattering features observed.

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“…These include rotational transfer (RT) [24,26,36,[38][39][40], i.e., state change within a vibrational manifold, vibration-rotation transfer (VRT) [41,42], i.e., transitions between vibrational states and electronic energy transfer [43], i.e., transitions between discrete levels of different electronic states. An example is given in Fig.…”

Section: Pðdj; Deþmentioning

confidence: 99%

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 multiple hard-ellipsoid model for rotationally inelastic collisions

Cited by 28 publications

References 18 publications

Collisional Properties of the OH Molecule

Collisional Properties of the OH Molecule

An analytic model of rotationally inelastic collisions of polar molecules in electric fields

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

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