Photodissociation spectroscopy of the [OCS⋅C2H2]+ cluster ion

The potential-energy surface features involved in the [OCS+C2H2]+ reaction system allow a metastable enroute to reaction to be trapped. The absolute photodissociation spectrum of this trapped metastable [OCS⋅C2H2]+ cluster ion has been measured in the wavelength region between 375 and 735 nm using a coaxial-laser–triple-quadrupole ion-beam apparatus. The photodissociation spectrum consists of at least three broad overlapping profiles, and OCS+, C2H+2, and C2H2S+ are the observed ionic photoproducts. The spectrum is interpreted in terms of transitions to excited charge-transfer states which are repulsive and to a dissociative transition which is localized on the perturbed OCS+ moiety. The C2H+2 fragment becomes detectable within sensitivity limits at 1.69 eV, yielding an upper limit estimate of 1.46 eV (+0.15/−0.23 eV) for the cluster bond dissociation energy. The C2H2S+ product is only observable at photon energies greater than 2.74 eV and is considered to be the product of a photoinitiated intracluster ion–molecule reaction.