Nitrogen quadrupole coupling constants for HCN and H2CN+: Explanation of the absence of fine structure in the microwave spectrum of interstellar H2CN+

Abstract

Nitrogen 14 quadrupole coupling constants for H₂CN⁺ and HCN are predicted via ab initio self‐consistent‐field and configuration interaction theory. Effects of electron correlation, basis set completeness, and geometrical structure on the predicted electric field gradients are analyzed. The quadrupole coupling constant obtained for H₂CN⁺ is one order of magnitude less than in HCN, providing an explanation for the experimental fact that the fine structure of the microwave spectrum of H₂CN⁺ has not been resolved. This research also allows a reliable prediction of the nuclear quadrupole moment of ¹⁴N, namely Q(¹⁴N)=2.00×10⁻²⁶ cm².