2, Pitchcombe Gardens, Coombe Dingle, Bristol BS9 2RH, UK
Abstract:
Watson’s theory of pure rotational spectra in nonpolar molecules is adapted to show that, if appropriate symmetry conditions are met, centrifugal distortion can lead to the appearance of the forbidden 0-0 origin band in an electronically forbidden spectrum. The intensity of such bands will be low; in the case of the benzene Ã1B2u-1A1g system the maximum intensity of the forbidden origin is estimated to be about 10−7 of that of the 610 band in the main vibronic spectrum. The prospects for the experimental detection of such weak bands are discussed.