Spectroscopic study of the Ne–Xe–NH3 van der Waals trimer

Abstract

Rotational spectra of the Ne–Xe–NH₃ van der Waals trimer were recorded using a pulsed-nozzle, Fourier transform microwave spectrometer. Both a- and b-type transitions of eight isotopologues, namely ²⁰Ne–¹³²Xe–¹⁴NH₃, ²⁰Ne–¹²⁹Xe–¹⁴NH₃, ²⁰Ne–¹³²Xe–¹⁵NH₃, ²⁰Ne–¹²⁹Xe–¹⁵NH₃, ²⁰Ne–¹³¹Xe–¹⁵NH₃, ²²Ne–¹³²Xe–¹⁵NH₃, ²²Ne–¹²⁹Xe–¹⁵NH₃, and ²²Ne–¹³¹Xe–¹⁵NH₃ were measured and assigned. Nuclear quadrupole hyperfine structures arising from the ¹⁴N (nuclear spin quantum number I = 1) and ¹³¹Xe (I = 3/2) nuclei were detected and analyzed. The determined rotational constants were used to fit structural parameters. A harmonic force field analysis was performed based on centrifugal distortion constants to extract information about vibrational motions of the complex. A comparison of van der Waals bond lengths and stretching force constants between the Ne–Xe–NH₃ trimer and the corresponding dimers indicates that non-additive three-body effects are present in the trimer system. Analyses of the ¹⁴N and ¹³¹Xe nuclear quadrupole coupling constants suggest that the NH₃ unit undergoes nearly free internal rotation within the complex and that the presence of Ne has little effect on the orientation of NH₃ with respect to the Xe atom.