The technique of velocity map imaging has been used to determine the dissociation energy of the C6H6+–Ar van der Waals complex. From the change in the ionization energy between the complex and free benzene and the spectroscopic shift of the S1←S0 transition, the dissociation energies in the S0 and S1 states of the neutral complex were determined, being 314 ± 7 and 335 ± 7 cm−1 for the S0 and S1 states of the neutral complex, respectively, and 486 ± 5 cm−1 for the cation ground (D0) state.

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On the authors' and employers' webpages: There are no format restrictions; files prepared and/or formatted by AIP or its vendors (e.g., the PDF, PostScript, or HTML article files published in the online journals and proceedings) may be used for this purpose. If a fee is charged for any use, AIP permission must be obtained. An appropriate copyright notice must be included along with the full citation for the published paper and a Web link to AIP's official online version of the abstract. The translational energy release distribution for dissociation of benzene-Ar has been measured and, in combination with the 6 1 0 rotational contour of the benzene product observed in emission, used to determine the rotational J,K distribution of 0 0 benzene products formed during dissociation from 6 1 . Significant angular momentum is transferred to benzene on dissociation. The 0 0 rotational distribution peaks at J = 31 and is skewed to low K : J average = 27, ͉K͉ 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 ͑2004͔͒, 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 prolate͒ 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.

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