Totally symmetric progressions in resonance Raman spectra and excitation profiles

Abstract

AbstractThe intensity distribution in totally symmetric progressions in resonance Raman spectra and excitation profiles is re‐examined with the aim of removing remaining discrepancies between theory and experiment. New low‐temperature intensity data are reported on the permanganate ion in a perchlorate pellet. New calculations are reported on this ion as well as on β‐carotene in carbon disulfide solution. The main conclusion is that a careful consideration of lineshapes and line broadening mechanisms is required and that intensities in resonance Raman spectra must not automatically be equated in peak heights. It is shown that the remaining discrepancies in MnO4− are due to the neglect of the nontotally symmetric modes which are Jahn‐Teller active and affect the totally symmetric excitation profiles through a breakdown of the Condon approximation. The theoretical model used to analyze β‐carotene is improved by the introduction of Gaussian lineshapes associated with inhomogeneous line broadening.