The State-selected Predissociation Dynamics of CClF₂NO Ã(n,π^*)

The photodissociation of gaseous CClF₂NO at 300 K and <20 K in a supersonic jet has been studied in the wavelength range 568 to 705 nm of the S₁(n,π^*)←S₀ electronic transition. Energy disposal into, rates of formation and product-state distributions of the nascent NO(X²Π_i) photofragment have been measured in detail, and have been compared with statistical (Prior) calculations. The rotational population distributions of the NO fragment are statistical up to the highest excess energies investigated, while the spin-orbit branching ratios are very non-statistical and non-thermal, favouring the lower component. The lack of evidence for state-specific effects in the energy disposal and appearance times of the NO indicate that excess energy randomises prior to dissociation. Intersystem crossing to T₁ dominates the predissociation of all but the lowest S₁ levels. Levels close to the O,O origin predissociate either by internal conversion to the ground state or by vibrational predissociation on an S₁ potential energy surface that is weakly bound in the dissociation coordinate. A bond dissociation energy of 13 700 ± 350 cm⁻¹ (164 kJ mol⁻¹) has been evaluated for the C—N bond.