Rotationally resolved spectra of transitions involving motion of the methyl groupof acetaldehyde in the system A~1A'-X~1A'

摘要

Fluorescence excitation spectra, at resolution 0.02 cm~(-1), in the system A ~1A"-X~1A' were recorded for acetaldehyde in a supersonic jet. We performed full rotational analysis analysis of bands 14_0~(0+) 15_0~n and 14_0~(0-) 15_0~n, for n = 0-4, in which 14~(0+) and 14~(0-) denote the two inversion tunneling components of the aldehyde hydrogen out of plane bending, in the vibrational ground state of A~1 A". Torsional levels from near the methyl torsional barrier to beyond that barrier are assigned. Sublevels of torsional symmetry A below the barrier are fitted as an asymmetric rotor, but the resulting values of the rotational parameter A are afected significantly by the torsional motion. For the E sublevels, K doublet states split significantly with torsional quantum number v_t. Anomalous transitions (#DELTA#K_a = 0, #DELTA#K_c = 0) to A sublevels are observed for bands 14_0~(0+) 15_0~4 and 10_0~(0-) 15_0~3, which cannot be simply explained from the Coriolis-type interaction of torsion and rotation.The positions of A and E sublevels in 14~(0-) 15~n cannot be fitted with a program involving only interaction of torsion and rotation, because for n = 0-2 states the A/E splitting is reversed from those in 14~(0+) 15~n. Interaction with inversion evidently varies the splitting of torsional sublevels and the K structure.