Translational energy (Et ) spectra of Cl and HCl fragments from vinylchloride, trans-dichloroethylene, cis-dichloroethylene, and 1,1′-dichloroethylene have been measured for the π*←π excitation at 193 nm. Et distribution and angular dependence of the Cl fragment indicate that the two-center dissociation occurs in a time faster than a rotation period and the recoiling organic radical (the counter fragment) is highly vibrationally excited. In dichloroethylenes, the presence of a second channel producing Cl atoms has been confirmed and attributed to the dissociation from the lower (n,σ*) state through a (π,σ*) state. The Et distribution of HCl fragments is nonstatistical and found to converge to null population at an energy less than half of the total available energy. This convergence point coincides with the value of the local available energy for the elimination reaction (activation energy —ΔH0reaction ). The yield of HCl molecules relative to Cl atoms is estimated to be ∼1.1 for vinylchloride. High efficiency of the HCl elimination is attributed to a rapid internal conversion from the (π,π*) state to the lowest (π,σ*) state from which the pathway to the transition state for HCl elimination is opened in ground electronic manifolds.

Articles you may be interested inOn the magnetic circular dichroism of aromatic carbonyl compounds

The polarized Raman and infrared spectra of [1H4]- and [2H4]pyridazines were studied. Assignments of the normal vibrations made by previous workers were reexamined on the basis of polarization behavior of the Raman and infrared bands and also through the normal coordinate calculation, and reasonable assignments are presented.

The near ultraviolet absorption spectrum of pyrazine vapor was photographed and measured. A tentative vibrational analysis was made for some of the bands in the longest wavelength discrete band system (3200 A system), due to the n — π transition. The spectral band feature shows that the 3200 A system is a superposition of two absorption systems which belong to different electronic transitions. It appears that this conclusion is also supported by simple theoretical considerations.

Pressure effects on the Raman active inter- and intramolecular vibrations of hexafluorobenzene crystals were studied under hydrostatic pressures up to about 5 GPa at room temperature in a gasketed diamond anvil cell. The observed Raman spectra indicate that very gradual application of pressure to hexafluorobenzene liquid up to about 0.3 GPa gives rise to supercompressed liquid and the supercompressed liquid crystallizes in phase I by further successive applications of pressure. On the other hand, hexafluorobenzene liquid crystallizes in phase II by quick application of pressure up to about 0.8 GPa. The crystal structure in phase I grown via supercompression is unchanged up to about 2—4 GPa, depending on the experimental conditions and finally transfers to phase II. Coexistence of the crystal phases I and II gives complex spectral structures in both the inter- and intramolecular vibrational regions under various pressures. The pressure-induced frequency shift of the intermolecular vibrations of hexafluorobenzene crystal is compared with those of hexachloro- and hexabromobenzene crystals and it is shown that the repulsive force between the bromine atoms belonging to different molecules is stronger than the repulsive forces between the fluorine atoms and also between the chlorine atoms.