Cl2 and HCl emissions in the ArF-laser photolyses of chlorinated compounds: Identification and mechanism of generation

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Abstract
The ArF (193.3 nm)‐laser photolyses of several chlorinated methanes and COCl2 were investigated using the unfocused beam. Cl2 and HCl emissions from highly excited states were observed and identified by use of recently calculated potential energy curves. The emissions were generated by absorption of two ArF‐laser photons. It was observed that the first absorbed photon forms an intermediate which subsequently absorbs the second photon to generate the fluorescent molecule. Some intermediates can also absorb a KrF‐laser photon to yield Cl2 emission. The intermediates were identified by energy restrictions to be Cl2 with excitation energies below the dissociation limit. In the cases of COCl2 and CCl4 this excitation extends up to the dissociation energy of Cl2(X). Also, vibrationally hot ground state HCl molecules are formed as intermediates. In some cases the intermediates contain the total energy available from the first photolysis step. Energy considerations result in an estimate for the heat of formation of the CHCl radical.