Excitation of Higher-Lying Metastable States in Carbon Monoxide by Electron Impact: Cross-Section and Lifetime Measurements

Abstract

The electron-impact cross section and radiative lifetime of the 10-eV metastable state in CO has been investigated from threshold (9.5\ifmmode\pm\else\textpm\fi{}0.4 eV) to 45 eV using a time-of-flight apparatus. The absolute cross section at the peak of the excitation function (15.5 eV) was estimated to be 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ to within a factor of 3. The radiative lifetime at 15 eV was found to be 97\ifmmode\pm\else\textpm\fi{}15 \ensuremath{\mu}sec. Measurements at 45 eV resulted in a smaller lifetime, suggesting the existence of more than one state. The assignment of the state as $b ^{3}\ensuremath{\Sigma}^{+}$ is rejected based on cross section and lifetime arguments, and the $D^{1}\ensuremath{\Delta}$ and $I ^{1}\ensuremath{\Sigma}^{\ensuremath{-}}$ states are suggested as alternate candidtates based on threshold considerations.