The rotational spectrum of chlorine trifluoride, ClF3. Centrifugal distortion analysis, Cl nuclear magnetic shielding tensor, structure, and the harmonic force field

Abstract

The rotational spectrum of the T-shaped ClF₃ was recorded for both ³⁵Cl and ³⁷Cl isotopomers in selected regions between 66 and 581 GHz. The observation of transitions involving J and K_a quantum numbers of up to 82 and 27, respectively, permitted the first centrifugal distortion analysis for this molecule. The quartic distortion constants were used together with data for the fundamental vibrations to derive harmonic force constants which were also calculated by means of ab initio methods. The harmonic force field and the rotational constants were employed to obtain ground state average (r_z) structural parameters and to estimate the equilibrium structure (r_e). Most of the rotational transitions showed resolved hyperfine splitting due to the ³⁵Cl or ³⁷Cl nucleus yielding, under consideration of previous data, accurate quadrupole coupling constants and, for the first time, nuclear spin–rotation coupling constants. While the former have been interpreted in terms of ionic bonding of the two different ClF bonds comparable to that in the ClF molecule, the latter were used to calculate nuclear magnetic shielding tensors.