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

The electron-impact cross section and radiative lifetime of the 10-eV metastable state in CO has been investigated from threshold (9.5±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×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ to within a factor of 3. The radiative lifetime at 15 eV was found to be 97±15 μsec. Measurements at 45 eV resulted in a smaller lifetime, suggesting the existence of more than one state. The assignment of the state as $b {}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ is rejected based on cross section and lifetime arguments, and the $D{}_{}{}^1{}_{}{}^{}\Delta$ and $I {}_{}{}^1{}_{}{}^{}\Sigma _{}^{-}{}_{}{}^{}$ states are suggested as alternate candidtates based on threshold considerations.