High-resolution spectroscopy of [H,C,N]+: III. Infrared Ã2Σ+ ← 2Π electronic transition of HCN+

Abstract

The òΣ⁺ ← ²Π electronic transition of the fundamental HCN⁺ ion is reported. The spectrum exhibits a rotational, fine, and hyperfine structure that provides insights into the geometries and wavefunctions of the òΣ⁺ and ²Π states. The extracted spectroscopic constants for the à state include (in cm⁻¹) T_e = 3238.8224(2), B = 1.39568(3), D = 2.27(9) × 10⁻⁵, γ = −0.07332(7), γ_D = 1.87(3) × 10⁻⁴, and the Fermi contact hyperfine constant for the HCN⁺ nitrogen atom b_F = 0.0059(1). Based on this value, the òΣ_1/2⁺ state electronic wavefunction is estimated to have 11.5 ± 0.2% s orbital character. The spin–orbit coupling constant for the state was also determined with high precision A_SO = −49.3122(4) cm⁻¹. This work illustrates that leak-out spectroscopy can be applied to measure high-resolution spectra of low energy electronic transitions.