Deexcitation rates forHe+(2S)in collision with atoms and molecules

Abstract

We have studied the deexcitation of ${\mathrm{He}}^{+}$ ions in the $2S$ metastable state by collision with eleven different target gases. These include noble gases, symmetric linear molecules, water, and ammonia. From our data we extract velocity-averaged total deexcitation-rate constants $〈\sigma v〉$ ranging from 1.65(17) × ${10}^{-9\mathrm{}}$ to 20.9(21) × ${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$ for helium and ammonia, respectively. In all cases the mean energy of the ${\mathrm{He}}^{+}$ ions was ≃0.23 eV and the target gases had a 300 °K Maxwell-Boltzmann distribution of velocities. The results are consistent with collision-induced Lyman $\alpha$ emission being a prominent deexcitation mechanism.