Chemical Dynamics of High Energy Molecules: The role of state density in collisonal relaxation

Elisa Miller
Boston University

Recent experimental studies in the Mullin lab suggest that state density in highly vibrationally excited donor molecules has a direct correlation to the amount of energy transferred to bath molecules, such as H2O and CO2. These studies used high-resolution transient infrared absorption probing to measure the rotational and translational energy gain in the bath molecule, following collisions with the highly excited donor molecules. Studies were performed on a series of high energy donors of increasing molecular complexity. The results revealed that highly vibrationally excited donor molecules with a higher state density are less likely to transfer an energy, ?E, in single impulsive collisions to the bath molecules than are donors in the lower state density. The extent to which the energy transfer distribution function changes with ?E, the amount of energy transferred, correlates to state density changes associated with those ?E values. This suggests that state density is a controlling factor in energy transfer and can be used to predict the shape of the ?E distribution function. This hypothesis has been constructed by comparing pyrazine, pyridine, 2-picoline, and 2,6-lutidine donor molecules energy transfer with CO2. The work reported here tests this hypothesis by taking high resolution IR transients to study the relaxation dynamics of 3- and 4-picoline, which have a similar state density to 2-picoline. Our results so far reveal that the rotational and translational energy gain of the CO2 with the new donors is similar to that of 2-picoline. This demonstrates that the 3- and 4-picoline will follow the same trend as the other donor molecules and is consistent with predictions based on state density.