ON THE COHERENT VIBRATIONAL PHASE IN POLARIZATION-SENSITIVE RESONANCECARS SPECTROSCOPY OF COPPER TETRAPHENYLPORPHYRIN

Polarization sensitive multiplex spectroscopy of resonance coherent an ti-Stokes Raman scattering (CARS) of copper(II)-tetraphenylporphyrin i n solution (CH2Cl2) is reported. The measurements were performed in th e Q band range of the porphyrin electronic absorption. Four polarized CARS spectra were resolved in 1300-1650 cm(-1) Raman range and were si multaneously fitted with a single set of vibrational parameters (band positions, bandwidths, amplitudes, depolarization ratios, and phases), The obtained coherent vibrational phases of A(1g), A(2g), and B-1g sk eletal modes of the porphyrin macrocycle appeared to correlate strongl y with the mode vibrational symmetry. The origin of such correlation i s analyzed within a model of the third-order nonlinear electric suscep tibility chi((3)), The proposed model is based on multidimensional dis placed harmonic oscillator in the Herzberg-Teller expansion of Raman p olarizability. The coherent vibrational phases of modes of different s ymmetry classes are directly affected by the symmetry dependent vibron ic couplings between the pairs of Q(x), Q(y) and B-x, B-y electronic t ransitions of the porphyrin. The phase contrast between the modes of v arious symmetries is most pronounced near the Q(00) resonance. (C) 199 7 American Institute of Physics.