15min:

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 ( \leq 0.02 dm³ mol^-1 cm^-1) in this region is due to the T₁(n, *) 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. % ₃₉', 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, *) excited state (via near-UV CRD spectroscopy). \begincenter Low-frequency fundamentals (cm^-1) of CHO vapor \vspace-.2in \endcenter \begindisplaymath

TABLE

\enddisplaymath For ₃₉ and ₃₇, the differences between S₁ and T₁ frequencies are noteworthy. These differences suggest that the electron delocalization associated with the ^* n chromophore in CHO is substantially different for singlet vs. triplet excitation.