Preresonance Raman scattering of overtones: The scattering of two overtones of benzene in the ultraviolet

Abstract

The Raman scattering of two vibrational overtones of benzene is found to undergo strong preresonance enhancement as the excitation frequency approaches the state, the lowest lying, forbidden electronic transition at 265 am. These preresonance active modes are the first overtone of the 606 cm-l eZS fundamental, which is responsible for the vibronidy induced 'Bzu intensity, and the first overtone of the 848cm-'el, fundamental, an out-of-plane C-H bending mode. In order to treat this overtone preresonance Raman behavior theoretically, the molecular polarizability is consistently expanded to second order in nuclear displacements, and thus we consider all preresonance contributions of this order. The leading contributions of strictly dipoleforbidden electronic transitions to fhe scattering cross-section of overtones are exposed. Within this theoretical context it is seen how scattering cross-section for each of these resonance active overtones is derived from different sources. The preresonance scattering of the 606 cm-' overtone results from the vibronic activity of this fundamental in the 'BZU transition. On the other hand, the 848crn-' overtone derives its lB2, resonance activity from the change in its fundamental frequency (to 585 cm-') in this excited electronic state. Furthermore, the 848 an-' overtone activity is built upon significant background preresonance contributions from other higher lying electronic transitions.

On band shapes of electronic transitions in the multimode weak coupling limit

“…Indeed, even for RRS of overtones, the nonadiabatic contributions formally just trail those obtained within the adiabatic approximation. 8 Still, since molecules like ZTBP appear to provide models for resolved, weakly coupled vibronic spectra, any asymmetry in their RRS excitation prOfiles could signal breakdown of the adiabatic approximation. However, from a simple phenomenological point of view, whenever DOS (or crowding) is operative, the peak of the absorption band will lie to the blue of the zero-zero transition.…”

UV Resonance Raman Studies of Molecular Structure and Dynamics: Applications in Physical and Biophysical Chemistry

“…This review outlines the recent progress in the development of UV resonance Raman spectroscopy (UVRR) as a new technique for the study of molecular structure and dynamics for both small molecules and larger molecules such as polypeptides and proteins. This recent work follows the pioneering UV Raman nucleic acid studies in 1975, which used frequency doubled Ar laser excitation at 257 nm (1)(2)(3)(4), and Ziegler & Albrecht's pioneering nitrogen-dye laser preresonance Raman benzene derivative studies, which set the stage for true resonance Raman investigations of benzene derivatives and other aromatics (5)(6)(7)(8). This work was followed ASHER -Ziegler & Hudson's UV resonance Raman benzene derivative studies excited at 212.8 nm using a quintupled Yag laser (9,10).…”

Chemical enhancement effects on protoporphyrin IX surface‐enhanced Raman spectra: Metal substrate dependence and a vibronic theory analysis

“…Secondly, the molecular transition polarizability is given by a sum of contributions over all electronic states as shown in Equation , where B 01 and B 02 correspond to the polarizability contribution from all the nonresonant states. As B 01 >> B 02 by a factor of [ 88 ] ~10 2 , cross‐term contributions between the resonant and nonresonant parts of the Raman polarizability can further reduce the relative intensity of overtones/combinations. Finally, it has been previously shown that the ratio of fundamental to overtone intensities is a function of the dephasing rate for resonant excitation.…”