Lifetimes of Metastable CO andN2Molecules

Abstract

The average lifetime of metastable CO molecules in the $a^{3}\ensuremath{\Pi}$ state excited by electron impact at 7.5 eV at room temperature was found to be about 1 msec. Lifetimes of metastable ${\mathrm{N}}_{2}$ molecules in the $a^{1}\ensuremath{\Pi}_{g}$ and $E^{3}\ensuremath{\Sigma}_{g}^{+}$ states were found to be 115 \ifmmode\pm\else\textpm\fi{} 20 and 190 \ifmmode\pm\else\textpm\fi{} 30 \ensuremath{\mu}sec, respectively. There was evidence for at least one higher-lying metastable state of CO at about 10eV having a lifetime of about 0.1 msec. The lifetimes were obtained in a time-of-flight experiment and deduced from the measurements without resorting to analytic expressions of the time-of-flight distribution. The observed time-of-flight distributions were essentially Maxwellian. A diffuse-gas source operated at pressures in the ${10}^{\ensuremath{-}4}$-Torr range was used. Effects due to metastable recoil, uv photons from metastable decay, and metastable wall collisions were carefully examined and found to be negligible under most conditions. Metastable excitation functions were obtained using a low-energy high-resolution electron gun.