Electronic excitation of CO by positron impact

We report calculated cross sections for the electronic excitation of carbon monoxide by positron impact. The calculations were carried out with the Schwinger multichannel method and included six collision channels, namely the ground (X (1)Sigma(+)) and five electronically excited (A (1)Pi, I (1)Sigma(-) and D (1)Delta) states. Present calculated excitation cross sections to the A (1)Pi state did not present any resonant features, being in this sense consistent with previous calculations for the isoelectronic nitrogen molecule. The experimental a (1)Pi(g) excitation cross section of N-2 presented a resonantlike structure which would also be expected in the A (1)Pi excitation of CO. We discuss possible reasons for the disagreement between experiment and theory.72