Neon matrix ESR investigation of 12C+2 and 13C+2 : Confirmation of a 4Σ−g ground electronic state

Abstract

The ¹²C⁺₂ and ¹³C⁺₂ cation radicals have been isolated in neon matrices by the photoionization of C₂(g) generated by the laser vaporization of thin carbon disks. A new procedure of supporting and thermally outgassing such targets for laser vaporization ESR studies in rare gas matrices is described. The ESR results confirm the ⁴Σ⁻_g ground electronic state assignment for C⁺₂ and provide a valence orbital electronic structure characterization based on the ¹³C hyperfine structure (hfs). The ESR lines are extremely narrow for a high‐spin powder sample and an intense off‐angle or ‘‘extra’’ absorption feature exibits unusual hfs. Normally forbidden (ΔM_S>1) transitions were detected at low magnetic fields. The magnetic parameters for ¹³C⁺₂ in a neon matrix at 4 K are: D=3668(3) MHz; g_⊥ =2.0018(5); g_∥ =2.0023(5); ‖A_∥‖ =99.4(8) MHz; and ‖A_⊥‖ =95.2(5) MHz.