The 2750 Å electronic band system of phenol: Calculation of out-of-plane frequencies and sequence intensities

Abstract

Force constant calculations are reported for the out-of-plane vibrational modes of phenol in its electronic ground state and first singlet excited state at 36349 cm −1, using a limited potential energy matrix of 22 nonzero elements. These calculations, which are exploratory in nature, were undertaken in an attempt to evaluate three questions of general interest, namely, (i) Can the intensity of the Δ v = 0 transitions (sequences) in an electronic spectrum be harnessed to check the assignment of nontotally symmetrical vibrations? (ii) Does the fact that the out-of-plane vibration frequencies of phenol in its electronic ground state are essentially the same as those of fluorobenzene indicate that the OH torsion is only loosely coupled to the phenyl modes? (iii) Is a C 2 v classification of practical value for the out-of-plane modes of phenol in either electronic state? It is found that (i) and (ii) can be answered affirmatively, with slight reservations. The C 2 v species are of some value in classifying displacements in the phenyl group, but may be misleading if applied indiscriminately.