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: #DELTA#_f H_0~0 (COFCl) = -397 +- 15 kJ mol~(-1) and D_0(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 COCl_2 allows conclusions to be drawn on the COCl_2 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.
展开▼
