Electronic spectra of N+2–(He)n (n=1, 2, 3)

Abstract

Ionic clusters of nitrogen and helium have been investigated by recording their electronic spectra in the near UV. Structured bands belonging to ¹⁴N⁺₂ –He, ¹⁴N⁺₂–(He)₂, ¹⁴N⁺₂–(He)₃, and ¹⁵N⁺₂ –He have been measured between 390 and 392 nm close to the N⁺₂ B ²Σ⁺_u←X ²Σ⁺_g band origin. Spectra were obtained by exciting mass selected cluster cations with tunable laser radiation and recording the photodissociation cross section as a function of wavelength. The data support the hypothesis that the He– – –N⁺₂ interaction potential has only a small barrier to internal rotation in both the X and B electronic states. A lower estimate for the dissociation energy of the N⁺₂ –He cluster of 101 cm⁻¹ is inferred.