Effect of geometrical conformation on the short-time photodissociation dynamics of 1-iodopropane in the A-band absorption

Abstract

We have taken resonance Roman spectra and made absolute Raman cross section measurements at six excitation wavelengths for 1-iodopropane. The resonance Raman spectra have most of their Raman intensity in features that may be assigned as fundamentals, overtones, and combination bands of three Franck-Condon active vibrational modes (the nominal C-I stretch, the nominal CCC bend, and the nominal CCI bend) for the trans and gauche conformations of 1-iodopropane. The resonance Raman and absorption cross sections of the trans and gauche conformations of 1-iodopropane were simulated using a simple model and time-dependent wave packet calculations. The results of the simulations were used in conjunction with the vibrational normal-mode coefficients to find the short-time photodissociation dynamics of trans and gauche conformers of 1-iodopropane in terms of internal coordinate changes. The trans and gauche conformers display significantly different Franck-Condon region photodissociation dynamics, which indicates that the C-I bond breaking is conformational dependent. In particular, there are large differences in the trans and gauche short-time photodissociation dynamics for the torsional motion (xGBx) about the GB carbon-carbon bond and the GBC angle (where C=α-carbon atom attached to the iodine atom, B=β-carbon atom attached to the α-carbon atom. G=methyl group carbon atom attached to the β-carbon atom). The major differences in the trans and gauche A-band short-time photodissociation dynamics can be mostly explained by the position of the C-I bond in the trans and gauche conformers relative to the plane of the three carbon atoms of the n-propyl group of 1-iodopropane. © 1998 American Institute of Physics.