The Ā2Πu → X̄2Πg electronic emission spectrum of the CI2+molecular cation

The 2Πu2Πg spectrum of Cl2+ has been recorded at a low rotational temperature in a crossed m molecular-beam/electron-beam apparatus. One hundred vibrational bands have been fitted into two Deslandres tables (one for Ω = 32, one for Ω = 12 components). The upper state is highly perturbed (especially the 32 subband), and vibrational quantum numbers have not been assigned. Analysis of the rotational structure near the band origins has confirmed the Ω value of some of the strong bands. Ab initio calculations predict that states arising from the electron configuration ...(σg)2(πu)4(πg*)2 (σu*)1 lie very close in energy to Ā2Πu(...(σg)2(πu)3(πg*)4), and we expect these states to mix heavily with Ā2Πu, causing the irregular vibrational energy level pattern. The radiative lifetime of Cl2+ Ā2Πu has been measured; it is invariant to υ' or Ω'. Finally, there appears to be an, as yet, unresolved discrepancy between the photoelectron spectrum of the second band of Cl2 (ionisation to Ā2Πu) and this optical emission spectrum of the ion.