The spectrum of HeAr +

Two band groups near 1450 Å, first observed by Tanaka, Yoshino, and Freeman ( J. Chem. Phys.62, 4484-4496 (1975)) in discharges through mixtures of helium and argon and assigned by them to the HeAr ⁺ ion, were studied under high resolution. Like the similar spectrum of HeNe ⁺ previously investigated, the spectrum of HeAr ⁺ is a charge transfer spectrum. The upper state B²Σ ⁺ of both band groups is derived from He⁺( ²S) + Ar( ¹S) while the two lower states A ₂²Π_{1}/{2} and X²Σ ⁺ are derived from He( ¹S) + Ar⁺( ²P) . All three states are very weakly bound, the two lower states even more weakly than the upper state. Unlike HeNe ⁺ most of the HeAr ⁺ bands are violet shaded. In the longward band group each band shows only three branches while in the shortward group there are four. The former observation shows that the A ₂²Π_{1}/{2} state behaves like a ²Σ ^- state with γ_v ≈ 0. The B, D, γ, p, and Δ G values of all states were evaluated. While the B_v values of upper and lower states are nearly equal, the D_v values are quite different and this difference accounts for the violet shading of most of the bands even when B' _v is slightly smaller than B″ _v; it also accounts for some of the extraheads and linelike features in the rotational structure. As in HeNe ⁺ the ²Π_{3}/{2} component of ²Π was not observed.