Photodissociation dynamics of carbonyl chloride fluoride and its implications for phosgene three body decay

Abstract

The photodissociation dynamics of COFCl has been studied by monitoring Cl fragments by resonance enhanced multi-photon ionisation and time-of-flight techniques at dissociation wavelengths near 235 nm. The COFCl heat of formation and the dissociation energy for C–Cl bond fission were for the first time experimentally determined: Δ_fH₀⁰ (COFCl)=-397±15 kJ mol^-1 and D₀(COF–Cl)=364±8 kJ mol^-1. 35% of the available energy is channelled into FCO rotation and bending vibration. The remaining energy is released as product translation. Other than in phosgene, no spin–orbit state selective behaviour is observed. The observations agree with a decay mechanism within the COFCl molecular plane as well as with a fragmentation via out-of-plane movement of the departing Cl atom. The structural and electronic similarity of COFCl and COCl₂ allows conclusions to be drawn on the COCl₂ dissociation. The findings are evidence for a previously proposed decay mechanism for the asynchronous concerted three body decay of phosgene into CO+2Cl. The first bond cleavage produces ground and excited spin–orbit state Cl and Cl*, respectively, with large kinetic energy release, while breaking the second C–Cl bond exclusively generates slow ground state Cl atoms.