Study of the Xe-NH3 van der Waals complex: High-resolution microwave spectra and ab initio calculations

摘要

An ab initio potential energy surface of the Xe-NH3 van der Waals complex was constructed at the coupled cluster level of theory with single, double, and pertubatively included triple excitations. The small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-zeta basis set was used for the Xe atom and Dunning's augmented correlation-consistent polarized valence triple-zeta basis set for the other atoms. The basis sets were supplemented with midbond functions. Rotational spectra of the Xe-NH3 van der Waals complex were recorded using a pulsed-nozzle Fourier transform microwave spectrometer. Rotational transitions within two internal rotor states, namely, the Sigma 0(0) and Pi 1(1)(lower) states, were measured and assigned to the Xe-(NH3)-N-14 and Xe-(NH3)-N-15 isotopologues. For the deuterated isotopologues, only the Sigma 0(0) states were observed. Two inversion components were observed for each state except for the "s" component of the Sigma 0(0) state of the Xe-(NH3)-N-14 and Xe-(NH3)-N-15 isotopologues, which has a spin statistical weight of zero. Nuclear quadrupole hyperfine structures arising from the N-14 (nuclear spin angular momentum quantum number I=1) and Xe-131 (I=3/2) nuclei were detected and analyzed. The observed spectra suggest that the Pi 1(1)(lower) state has lower energy than the unobserved Sigma 1(1) state, in contrast to the case of Ar-NH3. (C) 2008 American Institute of Physics.