We have obtained resonance Raman spectra and absolute Raman cross section measurements at five excitation wavelengths within the A-band absorption for 1-bromo-2-iodoethane in cyclohexane solution. The resonance Raman spectra have most of their intensity in the fundamentals, overtones, and combination bands of six Franck-Condon active vibrational modes; the nominal CCI bend, C-I stretch, C-Br stretch, C-C stretch, CH2 wag with the Br atom attached to the CH2 group, and CH2 wag with the I atom attached to the CH2 group. The resonance Raman intensities and A-band absorption spectrum were simulated using a simple model and time-dependent wave packet calculations. The simulation results and normal mode descriptions were used to find the short-time photodissociation dynamics in terms of internal coordinate displacements. The A-band short-time photodissociation dynamics for trans-1-bromo-2-iodoethane show that the C-I, C-Br, and C-C bonds as well as the CCI, CCBr, HCC, ICH, and BrCH angles have significant changes during the initial stages of the photodissociation reaction. This indicates the photodissociation reaction has a large degree of multidimensional character and suggests that the bromoethyl photofragment receives substantial internal excitation in so far as the short-time photodissociation dynamics determines the energy partitioning. Comparison of our results for 1-bromo-2-iodoethane with the A-band short-time dynamics of iodoethane, 1-chloro-2-iodoethane, and 1,2-diiodoethane and the trends observed for their A-band absorption spectra suggest that both the C-I and C-Br bonds experience a noticeable amount of photoexcitation.

We have taken resonance Raman 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 C5a-carbon atom attached to the iodine atom, B5b-carbon atom attached to the a-carbon atom, G5methyl group carbon atom attached to the b-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.

We examine the chemical reactions of the isodiiodomethane (CH2I-I),

We have obtained transient resonance Raman spectra of the [CH2CHCH2]+ (allyl cation) produced following C-band excitation of cyclopropyl bromide. The experimental resonance Raman spectrum display an overtone progression in the nominal [C=C=C]+ stretch mode and its combination bands with the CH=CH2 rocking modes. Density functional theory computations were performed to estimate the vibrational frequencies for the allyl cation, the allyl radical, the cyclopropyl radical, the cyclopropyl bromide molecule and the gauche-allyl bromide molecule and compared to the experimental vibrational frequencies. This comparison indicates that the allyl cation can be formed as a product of cyclopropyl bromide photodissociation in acetonitrile solution.

We report resonance Raman spectra of selected I2:olefin complexes obtained with excitation within the ～270nm absorption band of the complex. Most of the Raman intensity appears in the overtones and combination bands of the nominal I-I stretch and C=C stretch modes. Ab initio calculations were done to examine the structure of the ground state of the complex. The Raman vibrational frequencies and the ab initio optimized geometry indicate both the I-I and C=C bond order decrease moderately in the ground state complex.