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

We have studied the production, destruction, and lifetimes of the ${\mathrm{He}}_2\left(a{{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}\right)$ and $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ 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 μsec. The production rates for the ${\mathrm{He}}_2\left(a{{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}\right)$ and $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ metastable states are about 500 and 450 per incident 160-keV electron, respectively.