Internal dynamics and HF bond lengthening in the hydrogen-bonded heterodimer CH3CN⋯HF determined from nuclear hyperfine structure in its rotational spectrum

Abstract

Nuclear hyperfine structure has been resolved and analysed in each of the K= 0 and K= 1 components of the J= 2 â†� 1 transitions of the hydrogen-bonded heterodimers CH₃C¹⁵N⋯HF and CH₃C¹⁵N⋯DF to give the H, F nuclear spin–nuclear spin coupling constant D^HF and the D-nuclear quadrupole coupling constant χ^D, respectively, of these symmetric top molecules. The additional determination of unperturbed transition frequencies for the K= 0 and K= 1 components of the J= 3 â†� 2 and 4 â†� 3 transitions for each species has allowed an accurate evaluation of the rotational constants B₀ and the centrifugal distortion constants D_J and D_JK as follows: [graphic omitted]. Analysis of these spectroscopic constants leads to the following molecular properties of CH₃CN⋯HF: [graphic omitted].