Rotationally resolved spectra of transitions involving methyl torsion and C-C-O bend of acetaldehyde in the system of A~1A'-X~1A'

摘要

In the fluorescence excitation spectrum of acetaldehyde cooled in a supersonic jet, we performed a full rotational analysis of conbination bands 10_0~114_0~(0+)15_0~n and 10_0~114_0~(0-)15_0~n, n=0-4 in the system A~1A"-X~1A'. The vibrational frequency of the C-C-O bending mode is determined to be v'_(10)=373.163(3) cm~(-1). THe rotational structure sof combination bands 10_0~114_0~(0+)15_0~2, 10_0~114_0~(0-)15_0~2, 10_0~114_0~(0+)15_0~3, and 10_0~114_0~(0-)15_0~4 resemble the structures of 14_0~(0+)15_0~2, 14_0~(0-)15_0~2, 14_0~(0+)15_0~3, and 14_0~(0-)15_0~4, respectively, but the intense E lines observed for 14_0~(0-)15_0~3 are not found in 10_0~114_0~(0-)15_0~3. Torsional spacings observed in the C-C-O bend series are slightly smaller than those in the pure torsional series 14~(0+) and 14~(0-); these result from a decreased torsional barrier due to the C-C-O bending motion. Inversion spacings exhibit a pattern similar to those in the series 14~(0+) and 14~(0-). Reversed abnormal torsional sublevel A/E splittings are found for states n=0-2 of the 10~114~(0-) series, similar to those in the 14~(0-) series, For states n=3, the K rotational structures between the 14~(0+) and 10~114~(0+) series and for n=4, the 14~(0-) and 10~113~(0-) series are more similar than those between the pure torsion-inversion series 14~(0+) and 14~(0-). Hence, these experimental data imply that the interaction of the C-C-O bend with rotational structures of torsional states is smaller than that resulting from the aldehyde inversion.