Cross Sections for Collisions of the Second Kind in a Helium-Neon Discharge

The collisional transfer of energy between two excited states in a gas discharge may be described by a two-body inelastic cross section. The energy dependence of the two-body cross section for collisions of the second kind between the $\mathrm{He} 2{}_{}{}^1{}_{}{}^{}S$ metastable and $\mathrm{Ne} 3s_2$ states has been investigated. This process is primarily responsible for populating the upper level of the 6328-Å laser transition. Pulsed afterglow measurements were performed as a function of gas temperature and pressure. The experiments were conducted at low gas temperatures so that the effect of energy transfer from the helium metastable level to other nearby neon levels could be minimized. The measured decay rates departed substantially from that predicted by using an energy-independent cross section. A unit-step cross section for the $\mathrm{He} 2{}_{}{}^1{}_{}{}^{}S-\mathrm{Ne} 3s_2$ resonant transfer process with a value of (1. 0 ± 0. 15) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ and with a threshold energy corresponding to the energy difference between the two levels was determined.