THE FLUORESCENCE EXCITATION SPECTRA OF HCP AND DCP FROM $34000 CM^{-1}$ TO THE GROUND ELECTRONIC STATE DISSOCIATION
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Date
1994
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Ohio State University
Abstract
As an extension of our previous work, the fluorescence excitation spectra of HCP and DCP cooled in a supersonic expansion has been recorded from $34000 cm^{-1}$ to the dissociation limit of the ground state. Once the dissociation limit of the ground electronic state was crossed, a sharp reduction in fluorescence quantum yield was detected that has allowed a precise determination of the ground state dissociation limit for both species. In this region, nearly four times the number of bands reported via absorption have been observed. In agreement with previous investigations, most of the bands lying below $\sim 38000 cm^{-1}$ are characterised by a perpendicular transition moment and have been assigned to a single electronic state, the $\widetilde{A} ({^{1} A^{\prime\prime}})$ state. Attempts to model the $\tilde{A}$ state bending progression as a two-dimensional harmonic oscillator will be discussed. Above $38000 cm^{-1}$, the electronic spectrum becomes considerably more complex and many bands in this region remain unassigned. However, a series of bands characterized by a parallel transition moment can be readily distinguished from higher vibronic levels of the $\tilde{A}$ state and have been assigned to the $\tilde{C}$ state. The $0^{D}(K=0)$ band for the HCP $\tilde{C}$ slate lies at $38787 cm^{-1}$ with the $0^{D}(K=1)$ band lying $14 cm^{-1}$ above it. For the higher vibronic levels of the $\tilde{C}$ state, the K=1 levels fall below the K=0 levels as expected if the $\tilde{A}$ state were the lower Renner-Teller component of a $^{1} \Delta$ state.
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Author Institution: Department of Chemistry, Princeton University