Fluorescence spectra of isolated molecules in neon and argon matrices: assignment of the lowest emitting states

Highly structured fluorescence spectra are reported for molecules isolated in Ne and Ar matrices. Their excitation spectra are very similar to the gas-phase two-photon ionization spectrum of . Most of the bands seen in emission can be attributed to Herzberg - Teller or Jahn - Teller active modes and to combinations of these modes. The intensity distribution of the fluorescence bands is compared with calculated intensities and shows that the emission is of mixed singlet and character in Ne matrices in nearly equal proportions and of mixed singlet and character in Ar matrices, in a proportion of 4 to 1 in favour of the state. The band frequencies show that these three states are degenerate to within our experimental uncertainty and we estimate their gas-phase energy at . The assignment of ground-state vibrational band frequencies are rediscussed in the light of the present results.