Microwave spectra of the Ar–ND3 van der Waals complex and its partially protonated isotopomers

Abstract

Rotational spectra of the Ar–ND3 van der Waals complex were measured in the frequency range between 4 and 19 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The isotopomers studied include those with ND3, NHD2, and NH2D. A tunneling splitting due to the inversion of the ammonia subunit within the ground state of the complex was observed for all three isotopomers. This splitting cannot be measured in Ar–NH3 for spin statistical reasons. Nuclear quadrupole hyperfine structure of rotational transitions arising from the N14 nucleus was resolved and the corresponding nuclear quadrupole coupling constants were determined. A smaller nuclear quadrupole splitting arising from the deuterium nuclei was observed but not resolved. The ground state spectroscopic constants are compared with experimental and theoretical data previously reported for Ar–NH3. Additional transitions were observed for Ar–ND3 and assigned to the two inversion tunnelling states of an excited internal rotor state. A fit of the spectroscopic constants for these two states suggests the presence of a Coriolis perturbation along the lines of that observed in the microwave spectrum of Ar–NH3.

Spectroscopy of Σ00→Π10 Vibrational–Tunneling–Rotational Band in Rg · ND3 (Rg = Ne, Ar, Kr)

“…In this work we have refit the data obtained in our previous work (1), along with microwave data obtained from measurement of the rotational transitions of the complex in the ground state, by Wijngaarden and Jager (13). The standard deviation of the fit is about 2 kHz for microwave, and 0.4 MHz for submillimeter-wave data.…”

“…Recently, a series of experiments on Rg · ND 3 complexes were done by Wijngaarden and Jager (13,15,16) who reported the rotational spectra within the ground 0 0 states of the neon, argon, and krypton complexes, which were obtained in microwave FT experiments. This and the present data set are highly complementary.…”

“…1c. Of all the van der Waals complexes previously studied, Ar · NH 3 (4-11, 3, 12, 2) and Ar · ND 3 (13,1) are the simplest molecules exhibiting inversion-tunneling motion. The first studies of the Ar · NH 3 complex were done in the microwave region (4,5).…”

Potential energy surface and bound states of the NH3–Ar and ND3–Ar complexes

“…[12][13][14] The main difference compared to NH 3 -Ar is that the total wave function must now be symmetric with respect to the permutation of the D nuclei that have a spin I = 1, which results in the fact that the rovibrational states have nonzero nuclear spin statistical weights for all irreducible representations of the D 3h (M) group. 48 We have computed the first 20 eigenvalues of the Hamiltonian for each irreducible representation with J ranging from 0 to 10 using the method outlined above.…”

“…These studies have been complemented by the observation of transitions in the ν 1 + ν 3 band region of the complex 11 as well as spectroscopic measurements on the rotational states of ND 3 -Ar. [12][13][14] Several potential energy surfaces (PES) have been developed over the years in order to help the understanda) jloreau@ulb.ac.be ing of the spectrum of the complex. The first PES was constructed using Møller-Plesset perturbation theory up to second order (MP2).…”