Photofragment spectroscopy ofN22+

Abstract

${\mathrm{N}}_2^{2+}$ ions, produced by electron impact of ${\mathrm{N}}_2$, are observed to predissociate into ${\mathrm{N}}^{+}$+${\mathrm{N}}^{+}$ when irradiated by a dye laser at photon energies between 14900 and 19500 ${\mathrm{cm}}^{-1\mathrm{}}$. Five structured bands in the spectrum are associated with absorptions from $X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ ($v=0,1,2\mathrm{}$) into three predissociated levels of the $1{}_{}{}^1{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ state. The two highest levels of the $1{}_{}{}^1{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ are believed to dissociate by tunneling through the Coulombic barrier in its potential-energy curve, whereas the lowest level is predissociated by the $1{}_{}{}^1{}_{}{}^{}\Sigma _u^{-}{}_{}{}^{}$ state. Kinetic-energy analysis of the ${\mathrm{N}}^{+}$ photofragments establishes the energy of $X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ ($v=0\mathrm{}$) at 4.8±0.2 eV above the ${\mathrm{N}}^{+}$+${\mathrm{N}}^{+}$ dissociation asymptote and yields an adiabatic appearance potential of 43.6±0.2 eV. Molecular constants for the $X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ and $1{}_{}{}^1{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ states are determined.