Isotopologues of the NeHCl complex observed by chirped pulse Fourier transform microwave spectroscopy.

The weakly bound Ne·HCl van der Waals dimer is a prototype for studying large-amplitude motion in noncovalently bound systems. We report the microwave spectrum of eight isotopologues of Ne·HCl, five of which have not previously been observed by high-resolution spectroscopy. We examine trends in experimentally derived van der Waals stretching force constants and effective bond lengths that are strongly sensitive to isotopologue-dependent motional averaging along the hindered rotation coordinate. Finally, we report an updated semi-empirical three-dimensional morphed potential for the Ne·HCl dimer that is fitted to a large dataset including previous microwave, near-IR, and sub-millimeter wave data in addition to our new microwave data.