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MOLECULAR DYNAMICS IN ACETYULENE: EFFECTIVE HAMILTIONIAN MODELS AND OPTIMAL INTERMEDIATE STATES FOR DISPERSED FLUORESCENCE SPECTRA

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/12997

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Title: MOLECULAR DYNAMICS IN ACETYULENE: EFFECTIVE HAMILTIONIAN MODELS AND OPTIMAL INTERMEDIATE STATES FOR DISPERSED FLUORESCENCE SPECTRA
Creators: Solina, Stephani Ann B.; O'Brien, Jonathan P.; Polik, William F.; Field, R. W.
Issue Date: 1994
Abstract: From Dispressed Fluorescence(DF) and Stimulated emission pumping (SEP) spectra of acetylene, it is now known that the only Franck-Condon active modes for the $\widetilde{A} \leftrightarrow \widetilde{X}$ transition are the CC stretch $(\nu^{\prime}_{2})$ and the trans-bend $(\nu_{4})$. Energy placed into these zero order modes flows via intramolecular vibrational Redistribution (IVR) first into cis-bend $(\nu^{\prime}_{2})$ due to Darling--Dennison (DD) resonance; then, for initial states with CC Excited, into states containing at least one quantum of anti-symmetric CH stretch due to the ``2345” anharmonic $resonance.^{1,2}$ From a naive ``ball and Spring” model of acetylene, selective excitation in these modes is a plausible scheme for promoting the unimolecular isomerization of acetylene vinylidene. To further elucidate the dynamics of acetylene, we have bee using superpoplyed effective Hamiltonian, developed from the pervious SEP studies recorded at $7000 cm^{-1}$ to model the fractionation patterns of the zero-order stats. Highly quality dispersed fluorescence spectra of acetylene have been recorded utilizing the zero-point vibrational levels of the $\widetilde{A}$ state. These DF spectra reveal Franck-Condon bright feature state ad their early time dynamics as each bright state evolves it its own seprate superpolyad. Each superpolyad is labeled by three good quantum number $n_{resonance} n_{stretch}$, and $t_{total}$. The qualitative intensity and energy splitting pattern observed in each superpolyad permit refinement of the molecular constants, especially the resonance strength parameters. Proper scaling behaviour from one superpolyad to the next previous a stringent test of the multi-resonance model.
URI: http://hdl.handle.net/1811/12997
Other Identifiers: 1994-FB-05
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