PHOSPHORESCENCE SPECTRA OF 2 ROTATIONAL ISOMERS OF M-FLUOROBENZALDEHYDE

Phosphorescence spectra of m-fluorobenzaldehyde and its aldehyde deute rated derivative have been observed in the vapor phase at room tempera ture and in a methylcyclohexane matrix at 4.2 K. Paired band systems w ere detected for the vapor phase and for each of the two different cry stallographic phases, alpha- and beta-phases, and were attributed to t wo rotational isomers of the aldehyde group. Variable intensity change s between the two paired bands observed in the alpha-phase crystal are manifestations of the isomeric conversion in the ground state during crystallizations. An energy correlation of the rotational isomers betw een the lowest excited n pi singlet and triplet states is given for t he vapor phase and for the alpha-phase methylcyclohexane matrix.