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Reactions of atomic oxygen with complexes containing HCI are investigated and the OH product state distributions are compared to those observed for the corresponding reactions of HCI monomers. In previous studies of reactions of oC P) with HCI and hydrocarbon complexes, rotationally colder OH product state distributions were observed, when compared to the corresponding reactions of monomers. In contrast, we find that reactions of O( 1 D) with HCI clusters yield OH rotational distributions that are unaffected by the incorporation of HCI into a van der Waals complex. Quasiclassical trajectories are run on collisions of oxygen with HCI and Ar" ·HCI at 1 eV collision energies to investigate the differences in the dynamics of the OeD) and oC P) reactions. It is found that when the van der Waals complex is longer lived than the collision complex, rotational and vibrational cooling are observed. In contrast, when the dissociation of the van der Waals complex is prompt, compared to the collision complex lifetime, the effects of complex formation on the internal energy of the OH product become negligible. © 1998 American 1nstitute of

An attempt is made to characterize the increase in internal temperature that should accompany the partitioning of a single quantum of vibrational energy within a small SF6⋅Arn+ cluster ion. For each value of n, the kinetic energy release associated with unimolecular (metastable) decay is used to establish an initial temperature for the cluster ion; ∼950 cm−1 of vibrational energy is then deposited into the ν3 vibrational mode of the SF6 moiety (using a CO2 laser). This step promotes additional dissociation which is accompanied by an increase in kinetic energy. From a model due to Klots [J. Chem. Phys. 58, 5364 (1973)] photofragment kinetic energies are predicted on the assumption that energy from the photon is partitioned statistically and leads to an overall increase in the temperature of each ion. Comparisons of experimental and calculated results clearly show that the infrared photoexcitation of SF6 in the ν3 mode leads to incomplete energy randomization. An improved description of the energy relaxation process is provided on the assumption that SF6 undergoes partial vibrational relaxation to either the ν2 or ν4 mode. The energy difference (∼300 cm−1) is then randomized throughout each cluster ion, and is reflected in the magnitude of the measured kinetic energy release accompanying the loss of a single argon atom. The estimated time scale for this process is an order of magnitude faster than the experimentally measured time for the total relaxation of SF6 (ν3=1) in an argon matrix.

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Using two separate IR lasers, we have attempted to characterise the increase in internal temperature that should accompany the partitioning of a single quantum of vibrational energy within small SF, -(NO),+ cluster ions. An initial temperature is established by measuring a kinetic-energy release associated with the unimolecular (metastable) decay of each ion. Using a CO, laser, ca. 950 cm-' of the vibrational energy is deposited into the SF, moiety and with a CO laser, the (NO),,+ moiety is excited with ca. 1700 cm-I of vibrational energy. In both cases, the ions are observed to photodissociate and the corresponding kinetic-energy releases are measured. Using Klots' model ( J . Chem. Phys., 1973, 58, 5364), an attempt is made to predict the photofragment kinetic energies on the assumption that the energy of each photon is partitioned statistically and contributes to an overall increase in temperature for each ion. The results show that at the higher photon energy, events are dominated by angular momentum conservation; a factor that is not an integral part of the model. In contrast, the photoexcitation of SF, at ca.