Energy-gap dependence for inelastic collision-induced electronic transitions in N2+

Abstract

An optical-optical double resonance procedure is used to compare the relative populations of e/f spin components of the $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$(v=7) rotational manifold resulting from the collision-induced electronic transitions in ${\mathrm{N}}_{2}^{+}$ for the cases of large and small energy gaps. Rotational levels of the $^{2}\mathrm{\ensuremath{\Pi}}_{\mathrm{ui}}$(v=3 or 4) vibrational state of ${\mathrm{N}}_{2}^{+}$ are selectively populated with a pump laser. Transitions to rotational levels of the $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$(v=7) level due to collisions with bath gas helium atoms at room temperature are monitored by scanning the lines of the B-X(5,7) band with a second, probe laser. The relaxation pathways A(v=3)\ensuremath{\rightarrow}X(v=7) and A(v=4)\ensuremath{\rightarrow}X(v=7) traverse energy gaps (\ensuremath{\Delta}E) of \ensuremath{\sim}0 and \ensuremath{\sim}1760 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. Perturbation of the rotational levels of the ${\mathit{B}}^{2}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{u}}^{+}$(v=5) state by the ${\mathit{A}}^{2}$${\mathrm{\ensuremath{\Pi}}}_{\mathrm{u}1/2}$(v=17) manifold allows for the e/f, spin-rotation splitting of the lines of the B-X(5,7) probe laser scan to be resolved. The effects of these perturbations on the relative intensities of the B-X(5,7) lines have been taken into account. The intensity patterns for collision-induced transitions across the two widely different energy gaps are nearly identical, indicating that the propensities for this case have an insignificant energy-gap dependence. These detailed propensities from selectively excited rotational levels of the A(v=4 or 3) level to the individual, nearly degenerate rotational levels of the X(v=7) manifold are compared with theoretical models for inelastic scattering between $^{2}\mathrm{\ensuremath{\Pi}}$ and $^{2}\mathrm{\ensuremath{\Sigma}}$ electronic states.