Low temperature spectra of the1B1u1A1gtransition of C6H6, sym-C6H3D3and C6D6

Abstract
The low temperature thin-film absorption spectra of C6H6, sym-C6H3D3 and C6D6 in the 1 B 1u 1 A 1g transition region are analysed in terms of a 0, 0 crystal-field-induced origin, and v 18(e 2g ), v 7(b 2g ) and v 16(e 2g ) false origins. The 0, 0 + v 21g ) band is clearly resolved in sym-C6H3D3 whilst it merges with 0, 0 + v 7(b 2g ) in C6H6. Recent polarization measurements of the C6H6 2150 Å band are shown to be consistent with a 0, 0 assignment. The 0, 0 origin is also seen in the fluorescence excitation spectrum of crystal C6H6.