ROTATIONAL ANALYSES OF BANDS OF THE (A)OVER-TILDE1B1-(X)OVER-TILDE1A1SYSTEM OF CIS-GLYOXAL

Rotational analyses have been carried out for the 5(0)1, 5(1)0, and 5( 1)1 bands of the A1B1-X1A1 system of cis-glyoxal, where nu5 is the tot ally symmetric C-C=O bending frequency. The vibrational frequencies nu 5' = 103.81 cm-1 and nu5'' = 284.51 cm-1 are smaller than the correspo nding frequencies for trans-glyoxal by nearly a factor of two. A vibro nically induced band with a different type of rotational structure has been analysed and shown to be an a-type band. The coupling vibration is the out-of-plane C-H wagging vibration nu6(a2) and is similar in fo rm and frequency to the vibronically active nu8(b(g)) vibration for tr ans-glyoxal.