Photon driven charge transfer half-collisions: The photodissociation of CO2⋅O+2 cluster ions with resolution of the O2 product vibrational states

Abstract

The photodissociation dynamics of the CO2⋅O+2 cluster are studied in a crossed ion beam–laser beam apparatus from λ=590 nm to λ=357 nm. At all wavelengths only CO+2/O2 products are observed even though O+2/CO2 products are lower in energy by 1.71 eV. The absolute cross section for photodestruction of CO2⋅O+2 is measured and increases smoothly from less than 1×10−18 cm2 at 590 nm to approximately 7×10−18 cm2 at 357 nm. In the range 590–458 nm ground electronic state CO+2(X 2Π)/O2(X 3∑) products are formed. Arguments are made that indicate that the O2 product is selectively vibrationally excited to the highest level energetically allowed (ν=0,1, or 2 depending on the wavelength). Asymmetry parameter analysis indicates that the photoexcited state of CO2⋅O+2 accessed is repulsive and the cluster dissociates in times short compared to a rotational period. At 357 nm the mechanism changes. Arguments are made that unambiguously indicate the O2 product is electronically excited at this wavelength and the product states are CO+2(X 2Π)/O2(a 1Δ). In addition, 10%–25% of the photoexcited clusters at 357 nm may initially be formed in a bound state that subsequently vibrationally predissociates. The large majority of the products at this wavelength are formed by direct dissociation from a repulsive state, however, similar to the longer wavelength data.