Microwave spectra and nuclear quadrupole structure of the NH 3 –N 2 van der Waals complex and its deuterated isotopologues

The journal of chemical physics 149(22), 224305 (2018). doi:10.1063/1.5063346
The microwave spectrum of the NH$_3$–N$_2$ 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)-NH$_3$–(ortho)-N$_2$ 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)-NH$_3$–(para)-N$_2$ 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 $^{14}$N nuclei of NH$_3$–N$_2$ was resolved for both transitions, and the quadrupole coupling constants associated with the NH$_3$ and N$_2$ 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 NH$_3$ and the N$_2$ axis is about 66°. The average van der Waals bond lengths are slightly different for (ortho)-NH$_3$–(ortho)-N$_2$ and (para)-NH$_3$–(para)-N$_2$ and amount to 3.678 Å and 3.732 Å, respectively. Similar results for the deuterated isotopologues, ND$_3$–N$_2$, NHD$_2$–N$_2$, and NH$_2$D–N$_2$, and their nuclear spin isomers were also obtained thus confirming and extending the analysis for the parent NH$_3$–N$_2$ complex.
Published by American Institute of Physics, Melville, NY