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.

Resonance Raman spectra were obtained for cyclopropyl iodide in cyclohexane solution with excitation wavelengths in resonance with the A-band absorption spectrum. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mainly along the nominal C-I stretch and nominal C-C-I deformation normal modes accompanied by moderate motion along the nominal cyclopropyl ring breathing and ring deformation normal modes. A preliminary resonance Raman intensity analysis was done, and the results for cyclopropyl iodide were compared to previously reported results for several cyclic and noncyclic alkyl iodides.

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 have obtained resonance Raman spectra of iodocyclopentane in cyclohexane solution at three excitation wavelengths resonant with the A-band absorption. The A-band resonance Raman spectral bands can be assigned to fundamentals, overtones, and combination bands of seven axial conformer and eight equatorial conformer Franck–Condon active modes. The resonance Raman and absorption cross sections were simultaneously simulated using wave packet calculations and a simple model. The best fit parameters of the simulations and the normal mode descriptions were used to determine the A-band short-time photodissociation dynamics of the axial and equatorial conformers of iodocyclopentane. The axial and equatorial conformers exhibit noticeably different short-time photodissociation dynamics that suggest that the C-I bond cleavage process is conformation dependent. The axial conformer short-time photodissociation dynamics have larger changes in the carbon-carbon stretch and three carbon atombending motions as well as the torsional motion about the a and b carbon atom bond. The CCI bending motions for the axial and equatorial conformers of iodocyclopentane as well as previously reported results for the equatorial conformer of iodocyclohexane are significantly smaller than CCI bending motions found for most noncyclic iodoalkanes examined so far. This suggests that the cyclic backbone restricts the initial motion of the C-I bond cleavage along the CCI bend in iodocycloalkanes compared to the noncyclic iodoalkanes.

We have done ab initio calculations to find the equilibrium geometries, rotational/inversion barriers, and harmonic vibrational frequencies of several haloethyl radicals (XCH2CH2 and XCHCH3 where X=F, Cl, Br). One equilibrium and two transition conformations for XCH2CH2 (X=Cl, Br) and XCHCH3 (X=F, Cl, Br) were found on the calculated B3LYP/6-311++G(3df,3pd) potential energy surface. We discuss the effects of the halo substituents on the haloethyl radicals investigated. The C-X bonds of the equilibrium