Photodissociation of CO−3⋅H2O: Observation of the O−⋅H2O+CO2 product channel

Abstract

A new product channel, O−⋅H2O+CO2 was discovered in the photodissociation of CO−3⋅H2O. Experiments were conducted by crossing a mass selected 8 kV ion beam with a linearly polarized laser beam and measuring the kinetic energy distributions of the charged photodissociation products. Distributions were collected at photon energies of 2.41, 2.54, and 2.71 eV. By varying the angle between the ion and the laser polarization vector, product angular distributions were obtained. Relative photodissociation cross sections of this process were determined by comparisons with known processes: a) CO−3⋅H2O+hν→CO−3+H2O and b) CO−3+hν→O−+CO2. Ab initio calculations focusing on geometric structure and vibrational frequencies of the ground state of O−⋅H2O were performed using GAUSSIAN 82 and GAUSSIAN 88 programs. With both MP2/6-31G** and MP2/6-31+G* basis sets, the lowest energy structure obtained was quasilinear with an O−⋅⋅⋅H–O angle of 3°. Vibrational frequencies and rotational constants obtained from these calculations were employed in statistical phase space modeling. Phase space theory indicated a photoinduced ‘‘intracluster’’ reaction mechanism was responsible for this novel product channel.