High-resolution spectroscopy of [H,C,N]+ : III. Infrared A2Σ + ← X2Π electronic transition of HCN+

Abstract

The A2Σ+ ← X2Π electronic transition of the fundamental HCN + ion is reported. The spectrum exhibits rotational, fine, and hyperfine structure that provide insights about the geometries and wavefunctions of the A2Σ+ and X2Π states. The extracted spectroscopic constants for the A state include (in cm -1 ) Te =3238.8224(2), B=1.39568(3), D=2.27(9)×10-5 , γ=-0.07332(7), γD =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 A2Σ+1/2 state electronic wavefunction is estimated to have 11.5±0.2% s orbital character. The spin-orbit coupling constant for the X 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.