Dynamics of Atomic and Molecular Metastable States Produced in Electron-Bombarded Superfluid Helium

Abstract

We have studied the production, destruction, and lifetimes of the ${\mathrm{He}}_{2}(a{^{3}\ensuremath{\Sigma}_{\mathrm{u}}}^{+})$ and $\mathrm{He}(2^{3}S)$ metastable states of helium that are produced in electron-bombarded superfluid helium. The characteristic lifetime of a metastable molecule in the superfluid is shown to exceed 0.1 sec, while the lifetime of a metastable atom is only about 15 \ensuremath{\mu}sec. The production rates for the ${\mathrm{He}}_{2}(a{^{3}\ensuremath{\Sigma}_{\mathrm{u}}}^{+})$ and $\mathrm{He}(2^{3}S)$ metastable states are about 500 and 450 per incident 160-keV electron, respectively.