ORIENTATION ANALYSIS BY SIMULATION OF VIBRATIONAL SUM-FREQUENCY GENERATION SPECTRUM - CH STRETCHING BANDS OF THE METHYL-GROUP

A description is given of the procedure which simulates the spectral features of vibrational sum frequency generation (VSFG) spectrum by the nu(CH) stretching bands of the methyl group. Instead of assuming that alpha(zetazeta) alone is significant as in previous expressions for the molecular hyperpolarizability tensor,we have introduced a parameter r = alpha(xixi)/alpha(zetazeta) where alpha(zetazeta) and alpha(xixi) are the parallel and perpendicular components, respectively, of the Raman tensor associated with CH bond. The statistical aspects of molecular orientation and finite width of an infrared light source were also incorporated. A model calculation is presented of the signals from two-dimensionally arranged methyl groups to reveal the effects of the quantities on the spectral and angular profiles.