Microwave spectra and nuclear quadrupole structure of the NH3-N2 van der Waals complex and its deuterated isotopologues.

The microwave spectrum of the NH3-N2 van der Waals complex has been observed in a supersonic molecular jet expansion via broadband (2-8 GHz) chirped-pulse Fourier-transform microwave spectroscopy. Two pure rotational R(0) transitions (J = 1 - 0) with different hyperfine structure patterns were detected. One transition belongs to the (ortho)-NH3-(ortho)-N2 nuclear spin isomer in the ground K = 0 state reported earlier [G. T. Fraser et al., J. Chem. Phys. 84, 2472 (1986)], while another one is assigned to the (para)-NH3-(para)-N2 spin isomer in the K = 0 state not reported before (K is the projection of the total angular momentum J on the intermolecular axis). The complicated hyperfine structure arising from three quadrupole 14N nuclei of NH3-N2 was resolved for both transitions, and the quadrupole coupling constants associated with the NH3 and N2 subunits were precisely determined for the first time. These constants provided the dynamical information about the angular orientation of ammonia and nitrogen indicating that the average angle between the C 3 axis of NH3 and the N2 axis is about 66°. The average van der Waals bond lengths are slightly different for (ortho)-NH3-(ortho)-N2 and (para)-NH3-(para)-N2 and amount to 3.678 Å and 3.732 Å, respectively. Similar results for the deuterated isotopologues, ND3-N2, NHD2-N2, and NH2D-N2, and their nuclear spin isomers were also obtained thus confirming and extending the analysis for the parent NH3-N2 complex.