Nanosecond Time-Resolved Spectroscopy of then=2Levels in a High-Pressure He Discharge

Nanosecond time-resolved absorption spectroscopy is used to study the populations of the $2{}_{}{}^1{}_{}{}^{}P$, $2{}_{}{}^3{}_{}{}^{}P$, $2{}_{}{}^1{}_{}{}^{}S$, and $2{}_{}{}^3{}_{}{}^{}S$ levels in a high-pressure He discharge. At high pressures, the population of the $2{}_{}{}^1{}_{}{}^{}P$ level decays primarily through three-body molecular formation involving two ground-state He atoms at a rate of (3.5 ± 0.8) × ${10}^{-31\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$. The population of the $2{}_{}{}^3{}_{}{}^{}P$ level decays primarily as a result of mechanisms other than collisions involving ground-state He atoms.