JET-COOLED FLUORESCENCE EXCITATION-SPECTRA AND CARBONYL WAGGING AND RING-PUCKERING POTENTIAL-ENERGY FUNCTIONS OF CYCLOBUTANONE AND ITS 2,2,4,4-D(4) ISOTOPOMER IN THE S-1(N,PI-ASTERISK) ELECTRONIC EXCITED-STATE
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abstract
The jet-cooled fluorescence excitation spectra of cyclobutanone and its 2,2,4,4-d4 isotopomer have been recorded in the 305-335 nm region. The electronic band origin of the d0 molecule for the S 1(,*) state of A2 symmetry occurs at 30 292 cm-1 (30 265 cm-1 for the d4 molecule). The observed spectra consisting of more than 50 bands for each isotopomer involve V7, vg, and v9 (the three A1 ring vibrations) as well as v20(C=O in-plane wag), v26 (C=O out-of-plane wag), and v27 (ring puckering). Five bands associated with the excited vibrational states of v26 in the S 1(n,*) electronic state were observed for each isotopic species, and these were used to determine the one-dimensional potential energy functions for the C=O out-of-plane wagging. The C=O wagging angle was determined to be 39 and the barrier to inversion is 2149 cm-1 (2188 cm-1 for the deuteride). For the ring-puckering in the S1 state the lowest three vibrational energy spacings were found to be 106, 166, and 185 cm-1 as compared to values of 35, 57, and 65 cm-1 in the S0 ground state. Several ring-puckering potential energy functions with varying degrees of asymmetry are capable of reproducing the observed results. In all cases, however, the v=0 puckering state lies above any barrier to planarity. A two-dimensional potential function which fits the observed data was also determined in terms of the wagging and puckering coordinates. 1994 American Institute of Physics.
