Luminescent charge transfer in a beam of CO++ colliding with Ar, N2, H2, D2 and CO

Luminescent charge transfer of CO++(3Π,1Σ+) ions in a beam with several atomic and molecular target species in a scattering cell was observed at 60–2000 eVlab projectile energies. Emission from CO+(B 2Σ+→X 2Σ+) was spectrally analyzed with a resolution of up to 1 Å full width at half maximum. In the case of CO+++CO collisions, CO+(B) emission due to electron capture by the projectile and to target ionization were distinguished using isotopic substitution. CO+(A 2Π→X 2Σ+) emission from the ionized target was also observed in this reaction. Similarly, with N2 as a target, strong N+2(B 2Σ+u→X 2Σ+g) emission was observed. The absolute cross sections for CO+(B) formation are 1–5 Å2. The CO+(B) vibrational excitation at 2000 eV can be explained by Franck–Condon transitions from the CO++(3Π)/(1Σ+) beam components in the ratio 1:2. At low energy the product CO+ vibrational excitation is higher, especially from collisions with Ar. The vibrational population distribution differs from that derived from earlier translational energy spectra, possibly due to a different CO++(3Π/1Σ+) beam composition. The rotational excitation is in all cases strikingly low, even at low impact energy. This is ascribed to the large electron capture radius (∼2.8 Å).