Molecular distortion in the pyrazine triplet state. Analysis in terms of the MIDP experiments under polarized light

The distortion of the pyrazine molecule in its triplet excited state, as revealed by the appearance of the group theoretically forbidden bands in the sublevel phosphorescence, is analyzed in terms of the polarization of the originally forbidden bands in the sublevel phosphorescence. The experimental results together with some theoretical estimates lead to the conclusion that the pyrazine triplet state is distorted to C2h[C2(y)] due to the pseudo Jahn–Teller type vibronic coupling involving b2g(ν4) vibrational mode.