Spectroscopy and Dynamics of Jet-Cooled Styrene-Ammonia Clusters
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Date
1995
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Ohio State University
Abstract
The $S_{0} \leftrightarrow S_{1}$ absorption and emission spectra of styrene have been analyzed with the help of an ab-initio calculation. It was found that out-of-plane vibrations undergo, in general, a red shift upon electronic excitation, while in-plane ones are not appreciably changed. An important exception to this rule is the $\nu_{17}$ mode, which is similar the $\nu_{14}(b_{2u})$ mode of benzene - it shows a considerable frequency increase upon excitation. The analysis led to some new assignments of certain vibronic transitions. In addition, the spectra of styrene-ammonia adducts were recorded. Cluster formation affects the frequencies of some normal modes of $S_{1}$ to a small but easily measured extent. It was found that in general, out-of-plane modes were blue shifted with respect to the bare molecule, while in-plane modes were essentially unchanged. Vibronic bands leading to out-of-plane in the cluster appear to be less intense than in the bare molecule; in contrast, some bands at about $500 cm^{-1}$ are found to have a considerably more intense than the corresponding bare molecule ones. These bands are due to a mode similar to the $\nu_{6}(e_{1m})$ mode of benzene, responsible for the vibronic coupling that makes the $^{1}A_{g} \leftrightarrow ^{1}B_{2u}$ transition weakly allowed. The dissociation energy of the styrene-ammonia cluster was roughly determined, by recording the dispersed emission spectra following excitation of the cluster to different vibronic levels. It was found to be $650 \pm 100$ for $S_{1}$ and $600\pm 100$ for $S_{0}$.
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Author Institution: The Hebrew University of Jerusalem, Jerusalem, Israel