15min:
CAVITY RINGDOWN ABSORPTION SPECTRUM OF THE T1 (n, pi*) leftarrow S0 TRANSITION OF
2-CYCLOHEXEN-1-ONE.

KATHERINE L. ZABRONSKY, MICHAEL O. MCANALLY, DANIEL J. STUPCA, NATHAN R. PILLSBURY AND STEPHEN DRUCKER, Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, WI 54702.

The cavity ringdown (CRD) absorption spectrum of 2-cyclohexen-1-one (CHO) was recorded over the range 401.5--410.5 nm in a room-temperature gas cell. The very weak band system ( epsilon \leq 0.02 dm3 mol-1 cm-1) in this region is due to the T1(n, pi*) leftarrow S0 electronic transition. The 000 origin band was assigned to the feature observed at 24,558.6 \pm 0.3 cm-1. We have assigned about 25 vibronic transitions in a region extending from -200 to +350 cm-1 relative to the origin band. From these assignments we determined fundamental frequencies for several vibrational modes in the T1 excited state. % nu39', ring bending (or inversion)

The table below compares their frequencies to corresponding values measured for CHO vapor in the S0 electronic ground state (via far-IR spectroscopy)\footnote T.~L.~Smithson and H.~Wieser, J.~Chem.~Phys. 73, 2518 (1980); M.~Z.~M.~Rishard and J.~Laane, J.~Molec.~Struct. 976, 56 (2010). and the S1(n, pi*) excited state (via near-UV CRD spectroscopy). \begincenter Low-frequency fundamentals (cm-1) of CHO vapor \vspace-.2in \endcenter \begindisplaymath

TABLE

\enddisplaymath For nu39 and nu37, the differences between S1 and T1 frequencies are noteworthy. These differences suggest that the electron delocalization associated with the pi* leftarrow n chromophore in CHO is substantially different for singlet vs. triplet excitation.