Oxalyl chloride - A clean source of chlorine atoms for kinetic studies

Oxalyl chloride, (COCl)₂, has been characterized as a photolytic source of chlorine atoms for kinetic studies. UV absorption spectrum of oxalyl chloride, as well as the photodissociation yield of chlorine atoms resulting from the photodissociation of oxalyl chloride at 193 nm (ArF excimer laser) in helium as a bath gas at p_He = 1, 10, and 100 bar, were measured using laser pulsed photolysis-UV-vis transient absorption spectroscopy. The photodissociation yield of chlorine atoms was determined from the measurements of photodepletion of oxalyl chloride via its absorption at 210.0 nm as well as via 270-390 nm UV absorption build-up caused by molecular chlorine formed in the recombination of chlorine atoms. The photodissosiation yield of chlorine atoms (the number of Cl atoms appeared per one dissociated oxalyl chloride molecule) is independent of helium pressure over the pressure range 1 -100 bar. The photodissociation yields of chlorine atoms at 298 K were measured as 2.01 ± 0.08 and 1.97 ± 0.12 at p_He = 10 bar and p_He = 100 bar, respectively. The overall photodissociation of oxalyl chloride at 193 nm is described by the following stoichiometric equation: (COCl)₂ + hv(193 nm) → 2 CO + 2 Cl. Due to the absence of any additional reactive species in the final photodissociation products, its relatively large absorption cross-sections in the UV and low reactivity toward free radicals, oxalyl chloride is suggested as a convenient and "clean" photolytic source of Cl atoms for kinetic studies.