Photodissociation of atmospheric positive ions. I. 5300–6700 Å

Abstract

Photodissociation cross sections have been investigated for several positive ions of atmospheric importance in the wavelength region from 5300 to 6700 Å, using a drift tube mass spectrometer and a tunable dye laser. The dimer ions NONO+ and CO2CO+2 are observed to have large photodissociation cross sections (≳10−17 cm2) at these wavelengths. Three ions formed from oxygen cations O+4, CO+4, and O+2⋅H2O have photodissociation cross sections near 1×10−18 cm2, with the latter two ions exhibiting a threshold near 6200 Å. The cluster ions NO+⋅M, where M is H2O, N2, CO2, and N2O, are not observed to photodissociate, nor are H3O+⋅ (H2O)n=0,1,2. Upper limits on the photodissociation cross sections for these ions are established in the range 10−19–10−20 cm2. For many of the ions studied here reactions coupling the ion of interest with other species present in the drift tube and diffusion effects following interaction with the laser must be explicitly considered to establish values or limits for the photodissociation cross sections.