Rotational Excitation in Ion-Molecule Collisions. II. H+, D+, He+, Ne+, H2+ and D2+, on N2

Abstract

A study was made of the rotational line intensities in the (0, 0) band of the ${\mathrm{N}}_2^{+}$ first negative system produced by ion bombardment of ${\mathrm{N}}_2$ at 130°K. ${\mathrm{H}}^{+}$, ${\mathrm{D}}^{+}$, ${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{D}}_2^{+}$ projectile ions at energies of 600 eV to 10 keV were used. The distribution of rotational energy in the upper state of the first negative system was found to deviate from a Boltzmann distribution for projectile ion velocities below ${10}^8$ cm/sec. Excitation to high rotational states increased monotonically with decreasing projectile velocity. The band envelope of spectra excited by atomic ions displayed a characteristic shape different from that excited by the molecular ions. For atomic ion excitation the extent of excitation to high rotational levels appeared to be a function of projectile ion velocity only: The nature of the rotational transition probability function for the collision-induced excitation and the implication of rotational excitation to high states with respect to other types of experiments are discussed.