Experimental and Computational Study of the Gas-Phase Reaction of O( super(1)D) Atoms with VF sub(5)

The reactions of O( super(1)D) atoms with VF sub(5) at room temperature have been studied by time-resolved laser magnetic resonance at the buffer gas (SF sub(6)) pressure of 6 Torr. The O( super(1)D) atoms were produced by the photodissociation of ozone using an excimer laser (KrF, 248 nm). By monitoring the kinetics of FO radical formation, the bimolecular rate constant of O( super(1)D) consumption in collisions with VF sub(5) has been determined to be k sub(VF) sub(5) = (7.5 plus or minus 2.2) 10 super(-11) cm super(3) s super(-1). The branching ratio for the channel producing FO radicals (k sub(8a)) has been found to be k sub(8a)/k sub(VF) sub(5) = 0.11 plus or minus 0.02. Quantum chemical calculations at the CCSD(T)/CBS level of theory give evidence that the reactions of O( super(1)D) with VF sub(5) proceed via the VF sub(4)OF intermediate. The enthalpy of the reaction leading to this intermediate formation was calculated to be -245.8 kJ/mol. In qualitative agreement with the experimental results, the reaction channel O( super(1)D) + VF sub(5) arrow right FO + VF sub(4) (8a) turned out to be 72.9 kJ/mol energetically more favorable than the channel O( super(1)D) + VF sub(5) arrow right F + OVF sub(4) (8b). The dissociation enthalpy of the OVF sub(4) radical was calculated to be very low (18.1 kJ/mol); hence, the decay of OVF sub(4) to F + OVF sub(3) should proceed very fast. The molecular channel O( super(1)D) + VF sub(5) arrow right F sub(2) + VF sub(3)O, though being most favorable thermodynamically, is kinetically unimportant.