High-resolution spectroscopy of [H,C,N]+: II. Ground state rotational spectrum of HCN+ (2Π)

Abstract

The rotational spectrum of HCN⁺ has been measured between 270 and 520 GHz in a cryogenic ion trap instrument employing a double resonance vibrational-rotational scheme based on leak-out spectroscopy. A total of four transitions with quantum numbers ranging from J″ = 2.5 to 5.5 have been observed for the lowest-energy spin–orbit state ²Π_3/2 of this open-shell cation, which has an inverted ²Π electronic ground state. The transitions show well-resolved Λ-doubling components each displaying complex hyperfine splittings due to the presence of two nuclei with non-zero spins, ¹H (I = 1/2) and ¹⁴N (I = 1). The accurate transition frequencies and ground state spectroscopic parameters determined for HCN⁺ in this work will enable radio astronomical searches of this important cation in the interstellar medium.