Photoinduced charge-transfer dissociation in van der Waals complexes. II. Na2...ClCH3, Na2...(ClCH3)2, and Na...FPh

Abstract

van der Waals complexes Nam...(XR)n (R=CH3 and Ph; X=Cl and F) have been generated by crossing a beam of Na with a supersonic jet of halide molecules XR seeded with Ar. The complexes were identified and measured by photoionization time-of-flight mass spectrometry. Tunable visible radiation (530–680 nm) was used to measure the photodissociation spectrum (an ‘‘action spectrum’’) of these clusters. The peak cross section for photodissociation of Na2...(ClCH3)n (n=1 and 2) was found to be large (∼6 Å2) with its maximum at 635 nm for n=1 and at 615 nm for n=2. These peak wavelengths suggest that the primary route for photodissociation is excitation of the Nam followed by charge-transfer dissociation: Na2...(ClCH3)1,2 + hυ → [Na*2...(ClCH3)1,2]‡ → [Na+2...(ClCH3)1,2−]‡→products (the double dagger indicates a transition state). By contrast, the photodissociation of Na2+...(ClCH3) appeared to follow a direct mechanism involving the dissociation of the [Na–Na]+. For Na...FPh, two excited states of the complex (Π and Σ) were thought to be responsible for the two broad peaks in the action spectrum, each with vibrational structure.