Electron Impact near theaΠ3State of CO: Dipole-Dominated Resonances

Sharp structures have been observed in the elastic and vibrational ($v=1\mathrm{}$ and $v=2\mathrm{}$) cross sections of the ground electronic state of CO at energies coincident with the $v=0, 1, \mathrm{and} 2$ levels of the $a{}_{}{}^3{}_{}{}^{}\Pi$ state of CO. The large electric dipole moment of the $a{}_{}{}^3{}_{}{}^{}\Pi$ state of CO (1.38 D) appears to be sufficient to bind temporarily the incoming electron at or near the top of the potential well. The potential energy curve for this "dipole-dominated resonance" coincides with that of the $a{}_{}{}^3{}_{}{}^{}\Pi$ state.