Bond-breaking in quantum state selected clusters: Inelastic and nonadiabatic intracluster collision dynamics in Ar–H2O→Ar+H(2S)+OH(2Π1/2,3/2±;N)

Abstract

High-resolution vibrationally mediated IR+UV photodissociation methods are used to investigate the dynamics of H–OH bond breaking in quantum state selected H2O and Ar–H2O van der Waal complexes prepared in a slit supersonic jet expansion. This capability is based on the following strategy: (i) Specific rovibrational quantum states of the Ar–H2O dimer and H2O monomer are optically selected in the second overtone (vOH=3←0) region with an injection seeded, Fourier transform limited (Δν≈160 MHz) optical parametric oscillator. (ii) Selective H–OH bond cleavage of the vibrationally excited H2O subunit in the cluster is achieved by 248 nm or 222 nm UV photolysis. (iii) Multibody collision dynamics between the H, OH, and Ar photofragments are probed via laser induced fluorescence (LIF) on the asymptotic OH rotational, lambda-doublet and spin–orbit distributions. Comparison between cluster (Ar–H2O) and monomer (H2O) data explicitly samples the influence of the Ar “solvent” on the UV photolysis dynamics and in particular highlights the dominant role of intracluster collisions as the fragments recoil. Most importantly, the OH fine structure distributions are found to be dramatically different for Ar–H2O vs H2O photolysis, indicating the major contribution of nonadiabatic events in the photofragmentation dynamics.