Abstract
The relaxation of highly vibrationally excited pyridine-h5, pyridine-d5, and pyridine-f5 (E approximately 38,000 cm(-1)) through collisions with water was investigated by high resolution transient IR absorption spectroscopy to investigate how preferential hydrogen bonding interactions impacts the energy transfer dynamics. Nascent rotational and translational energy gain profiles for scattered H2O(000) molecules with E(rot) > 1000 cm(-1) are reported. H2O(000) molecules scattered from pyridine-h5 and pyridine-d5 have rotational distributions with T(rot) = 890 K. Less rotational energy is found in H2O(000) scattered from pyridine-f5 for which T(rot) = 530 K. The recoil energy distributions are similar for the three donors with T(rel) = 400-700 K. To explain the results, a torque-inducing mechanism is proposed that involves directed movement of water between sigma and pi-hydrogen bonding interactions with the pyridine donors. The experimental results are consistent with this mechanism, and with effects due to the state-density energy dependence of the highly excited donor molecules. Differences in vibrational mode frequencies of the hot donor molecules do not appear to explain the experimental results.
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