Nonresonant hyper‐Raman and hyper‐Rayleigh scattering in benzene and pyridine

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/90/9/10.1063/1.456592.Nonresonant hyper‐Raman and hyper‐Rayleigh spectra excited at 1064 nm are reported for neat benzene and pyridine. The theory of Herzberg–Teller vibronic coupling in nonresonant and preresonant hyper‐Raman scattering is developed. Nonresonant hyper‐Raman scattering is shown to be vibronically induced by modes that efficiently couple strongly allowed one‐photon and two‐photon transitions. A weak and broad (55 cm− 1) hyper‐Rayleigh band was observed in benzene and attributed to collective scattering, while in pyridine, a much more intense and much narrower hyper‐Rayleigh band was observed. Only the a 2u vibration (ν1 1) was observed in the hyper‐Raman spectrum of benzene, while several strong bands were observed in pyridine. Possible vibronic‐coupling pathways are discussed for these modes. In addition, the observed hyper‐Raman spectrum of pyridine is compared to a recent calculation