A new method for observing the rotational spectra of weak molecular complexes: KrHCl

Abstract

A new method of observing the rotational transitions of weak molecular complexes by combining the techniques of microwave Fourier transform spectroscopy, a Fabry–Perot cavity, and a pulsed nozzle source of molecules is described. High resolution and good sensitivity are achieved. Twelve isotopic species of the KrHCl molecule involving all combinations of the ⁸⁶Kr, ⁸⁴Kr, ⁸²Kr, H, D, ³⁵Cl, and ³⁷Cl isotopes are assigned and the rotational constants, Cl nuclear quadrupole coupling constants, and centrifugal distortion constants are all given. The molecular structure indicates a linear equilibrium structure with the H(D) atom between the Kr and Cl atoms. However, the inverse moments of inertia measured here indicate large amplitude vibrations of the H(D) atom relative to the Kr–Cl internuclear line. Estimates of the Kr–Cl stretching frequency and force constants, which show considerable dependence on the isotopic species, are also given. Bending frequencies and force constants are also given.