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Type: Journal article
Title: Rotational distributions following van der Waals molecule dissociation: comparison between experiment and theory for benzene-Ar
Author: Sampson, R.
Bellm, S.
McCaffery, A.
Lawrance, W.
Citation: Journal of Chemical Physics, 2005; 122(7):074311-1-074311-9
Publisher: Amer Inst Physics
Issue Date: 2005
ISSN: 0021-9606
Statement of
Rebecca K. Sampson, Susan M. Bellm, Anthony J. McCaffery, and Warren D. Lawrance
Abstract: <jats:p>The translational energy release distribution for dissociation of benzene–Ar has been measured and, in combination with the 610 rotational contour of the benzene product observed in emission, used to determine the rotational J,K distribution of 00 benzene products formed during dissociation from 61¯. Significant angular momentum is transferred to benzene on dissociation. The 00 rotational distribution peaks at J=31 and is skewed to low K:Javerage=27, ∣K∣average=10.3. The average angle between the total angular momentum vector and the unique rotational axis is determined to be 68°. This indicates that benzene is formed tumbling about in-plane axes rather than in a frisbeelike motion, consistent with Ar “pushing off” benzene from an off-center position above or below the plane. The J distribution is very well reproduced by angular momentum model calculations based on an equivalent rotor approach [A. J. McCaffery, M. A. Osborne, R. J. Marsh, W. D. Lawrance, and E. R. Waclawik, J. Chem. Phys. 121, 1694 (2004)], indicating that angular momentum constraints control the partitioning of energy between translation and rotation. Calculations for p-difluorobenzene–Ar suggest that the equivalent rotor model can provide a reasonable prediction of both J and K distributions in prolate (or near prolate) tops when dissociation leads to excitation about the unique, in-plane axis. Calculations for s-tetrazine–Ar require a small maximum impact parameter to reproduce the comparatively low J values seen for the s-tetrazine product. The three sets of calculations show that the maximum impact parameter is not necessarily equal to the bond length of the equivalent rotor and must be treated as a variable parameter. The success of the equivalent rotor calculations argues that angular momentum constraints control the partitioning between rotation and translation of the products.</jats:p>
Keywords: Molecular collisions
gas mixtures
phase control
molecular orientation
Rights: © 2005 American Institute of Physics
DOI: 10.1063/1.1847512
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