dc.creator Springer, M. G. en_US dc.creator Jagusch, S. P. en_US dc.creator Hlavacek, N. C. en_US dc.creator Drucker, S. en_US dc.date.accessioned 2008-07-15T13:27:12Z dc.date.available 2008-07-15T13:27:12Z dc.date.issued 2008 en_US dc.identifier 2008-TG-08 en_US dc.identifier.uri http://hdl.handle.net/1811/33246 dc.description R. A. Back and R. D. Gordon, J. Molec. Spectrosc. en_US dc.description Author Institution: Department of Chemistry, University of Wisconsin-Eau Claire; Eau Claire, WI 54702 en_US dc.description.abstract The cavity ringdown absorption spectrum of 4-cyclopenten-1,3-dione (CPD) was recorded near 487 nm in a room-temperature gas cell. The very weak band system ($\epsilon <$ 0.05 dm$^3$ mol$^{-1}$ ${\rm cm}^{-1}$) in this region is due to the $T_1(n, \pi$*$) \leftarrow S_0$ electronic transition. The origin band was observed at \mbox{20,541$\pm 1$ ${\rm cm}^{-1}$}. We have assigned 15 vibronic transitions in a region extending to about \mbox{$+700$ ${\rm cm}^{-1}$} relative to the origin band. From these tentative assignments we determined fundamental frequencies for several vibrational modes in the $T_1$ excited state. These include the out-of-plane ring modes $\nu_{19}'$ ($b_1$) and $\nu_{14}'$ ($a_2$). The table below compares their frequencies to corresponding values} {\bf 204}, 85 (2000).} in the $S_0$ electronic ground state and the $S_1(n, \pi$*$)$ excited state. \begin{center} Ring frequencies (cm$^{-1}$) of CPD in its lowest electronic states \vspace{-.2in} \end{center} \begin{displaymath} \begin{array}{ccccc}\hline \rule[0mm]{0mm}{3mm} {\rm Mode} & {\rm Description} & S_0 & S_1 & T_1 \\ \hline \rule[0mm]{0mm}{3mm} \nu_{19} & {\rm pucker} & 99 & 160 & 106 \\ \nu_{14} & {\rm twist} & 239 & 307 & 299 \\ \hline \end{array} \end{displaymath} The increases in these ring frequencies upon electronic excitation signify that the nominal $n \rightarrow \pi^*$ chromophore is delocalized to include the conjugated ring atoms. It is noteworthy, though, that the $\nu_{19}$ fundamental increases by only 7 cm$^{-1}$ upon $T_1 \leftarrow S_0$ excitation, compared to 61 cm$^{-1}$ for the $S_1$ excitation. Other cyclic conjugated enones show differences ($S_1$ vs.\ $T_1$ ring frequencies) of similar magnitude. These findings are attributable to the configuration mixing that each of the excited states undergoes. The two $n,\pi^{*}$ excited states may undergo mixing within distinctly different manifolds of spin-orbitals. en_US dc.language.iso English en_US dc.publisher Ohio State University en_US dc.title CAVITY RINGDOWN ABSORPTION SPECTRUM OF THE $T_1 (n,\pi^{*}) \leftarrow S_0$ TRANSITION OF 4-CYCLOPENTEN-1,3-DIONE en_US dc.type Article en_US
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