Electronic states of 1,3,5-sym-triazine. II. Geometry of the E-1 '' and E-3 '' states in the crystal

Through Stark, Zeeman, Zeeman-Stark, and absorption spectra of h(3)-, h(2)d(1)-. h(1)d(2)-, and d(3)-sym-triazine isotopes it has been determined that the lowest observed ringlet-ringlet transition (E-1" - (1)A(1)'. assigned in the gas phase) and ringlet-triplet transition (E-3" <- (1)A(1)', predicted experimentally and theoretically) of this molecule are bush crystal field split by at least ca 200 cm(-1) in the low temperature monoclinic crystal. The observed sharp crystal origins for ringlet and triplet regions are assigned to transitions involving one component of the split E-1" and E-3" excited states, respectively. From h(2)d(1)-, and h(1)d(2)-sym-triazine absorption intensity ratios for these transitions, it has been demonstrated that the excited state geometry is "quinoidal" (i.e., four long and two short bonds) at 4.2 degrees K in each excited state.