RESONANCE RAMAN-SPECTRA AND QUANTUM-CHEMICAL VIBRATIONAL ANALYSIS OF THE C7H7-CENTER-DOT AND C7D7-CENTER-DOT BENZYL RADICALS

Time-resolved resonance Raman (RR) spectra of the benzyl radical and i ts perdeutero isotopomer are presented. The radicals are created by la ser flash photolysis (lambda=266 nm) of benzylchloride in solution. Th e spectra are excited at a wavelength of 315 nm, in resonance with the intense D-3(2(2)A(2))<--D-0(1(2)B(2)) transition. Twenty Raman bands, both polarized and depolarized, are observed. The RR spectra are anal yzed through quantum chemical force field for p electrons (QCFF/PI) an d ab initio calculations of equilibrium geometries, vibrational freque ncies, Franck-Condon factors, and vibronic interactions. Polarized int ense bands are assigned to totally symmetric a(1) modes, and a number of depolarized bands to fundamentals of b(1) modes. The observed activ ity of b(1) modes suggests vibronic coupling, which is confirmed theor etically by calculations of vibronic interactions between the D-3(2(2) A(2)) and D-5(4(2)B(2)) states. The results from semiempirical and ab initio calculations are compared with experiment. The contributions of the different internal coordinates to the normal modes are calculated together with the changes in the molecular structure upon electronic excitation from D-0 to D-3 and D-5.