HIGH-TEMPERATURE VAPOR-PHASE RAMAN-SPECTRA AND ASSIGNMENT OF THE LOW-FREQUENCY MODES OF TRANS-STILBENE AND 4-METHOXY-TRANS-STILBENE

The vapor-phase Raman spectra of trans-stilbene at 330 degrees C and 4 -methoxy-trans-stilbene at 350 degrees C have been recorded using a sp ecially constructed high temperature cell. Together with the dispersed fluorescence spectra, these spectra have been used to assign the eigh t low-frequency vibrational modes in each molecule. For trans-stilbene , strong polarized bands at 273 and 152 cm(-1) were ascribed to the to tally symmetric nu(24) (C-e-phenyl bend) and nu(25) (in-plane phenyl w ag), respectively. A depolarized band at 207 cm(-1) was assigned to th e B-g phenyl flap (nu(47)), and a polarized shoulder near 125 cm(-1) i s believed to result from both the B-g phenyl torsion (nu(48)) and the overtone of the A(u) phenyl flap (nu(36)) For 4-methoxy-trans-stilben e the C-e-phenyl bend and in-plane phenyl wag were shifted to 234 and 144 cm(-1), respectively. These assignments were critical for understa nding the fluorescence spectra associated with the torsional motions.