Resonance Raman Spectroscopy of Dissociative Polyatomic Molecules

Abstract

Resonance Raman spectroscopy as a probe of the early stages in the dissociation dynamics of polyatomic molecules has become a valuable complement to photofragmentation studies. While these spontaneous Raman experiments are obtained in the frequency domain, they often reflect evolution of the molecule during the first few femtoseconds of bond breaking. Coupled with progress in classical and quantum calculations of large-amplitude motion, unique insights have become available for a number of small polyatomic molecules. The development of this field to date is reviewed.

A detailed experimental and theoretical study of the femtosecond A-band photodissociation of CH3I

“…Thus, dynamical reasons related with the couplings between modes and the nonadiabatic crossing may be behind this effect. The only previous ͑indirect͒ reference to this phenomenon is the work by Johnson et al, 25 where in a frequency domain Raman spectroscopy experiment, they found evidence suggesting that the extension of the C-I bond temporally precedes the onset of the conversion of CH 3 from its tetrahedral configuration to its ultimately planar geometry ͑umbrella motion͒ in a few femtoseconds. We have observed this type of behavior directly, but in the CH 3 symmetric stretch motion, with a fundamental frequency of 3004 cm −1 versus the 607 cm −1 of the umbrella mode.…”

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

“…This actually allows us to study the photodissociation dynamics of both cold and hot methyl radicals simply by choosing different radical products with time delays. CH 3 I photodissociation has been studied extensively and most of the present knowledge on the CH 3 I photodissociation dynamics involving the A band have been provided in several recent theoretical studies [13][14][15] and a recent review article by Kinsey et al 16 Recently, the nascent quantum state product distributions corresponding to both I( 2 P 3/2 ) and I( 2 P 1/2 ) have been fully determined by Eppink and Parker using the velocity map imaging technique. 17 There are two groups of CH 3 radicals ͑fast and slow͒ corresponding to the two I atom product states.…”

Photoelectron spectroscopy of ammonia via a fast predissociative state

“…Among them, a A 3 resonance Raman spectroscopic study of the state revealed a progression of stretching NH 3 A 3 vibrations.6,7 Resonance Raman spectroscopy, as pioneered by Kinsey et al 8,9 has demonstrated that the wavepacket motions during the dissociation are reÑected in the Raman spectrum thus resulting in a long progression of vibrations following the FranckÈCondon principle. 10 The photoelectron spectrum resulting from REMPI via a dissociative intermediate state can be viewed just as a resonance Raman with replacement of the spontaneous emission by a stimulated transition. Recently, such experiments have also been successfully demonstrated on by PES and CH 3 I ZEKE.11,12 Other spectroscopic studies have contributed to the measurement of predissociative linewidths of the state ranging from 38 to 300 cm~1 for di †erent levels.13 Further-NH 3 A 3 (l 1 , l 2 ) more, the potential energy surface of the state has been computed ab initio by Rosmus et NH 3 A 3 al.…”