Fine structure branching ratios and Doppler spectroscopy of chlorine atoms from the photodissociation of alkyl chlorides and chlorofluoromethanes at 157 and 193 nm

摘要

Alkyl chlorides (R=CH3, C2H5, C3H7, and C4H9), chloromethanes (CHnCl4minus;n), and chlorofluoromethanes (CFnCl4ndash;n) are photodissociated at 157 and 193 nm. The chlorine atom photofragments are detected by a resonance enhanced multiphoton ionization technique. The branching ratios of the Cl photofragments lsqb;Clast;(3p2P1/2)rsqb;/lsqb;Cl(3p2P3/2)rsqb; are almost identical (0.23plusmn;0.03) for alkyl monochlorides at 157 and 193 nm and for CH2Cl2and CHCl3at 157 nm, while the ratios are rather small (0.10plusmn;0.02) for CH2Cl2and CHCl3at 193 nm. No discernible isotope effects on the branching ratios were observed when D atoms were substituted for H atoms in chloromethanes. For CCl4, CF3Cl, CF2Cl2, CFCl3at 157 and 193 nm, the ratios are small (0.05) irrespective of the number of Cl atoms in the parent molecules. The Doppler profiles of the chlorine photofragments have been obtained and it is found that (a) CF3Cl undergoes a perpendicular optical transition at 157 nm and (b) for halomethanes containing more than two Cl atoms, the Cl photofragment has a Boltzmann distribution in translational energy and an isotropic angular distribution.