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

Journal of Chemical Physics. 2018. Vol. 149. No. 22. P. 224305-1–224305-6.

Leonid Surin

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 theNH3 andN2 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 C3 axis of NH3 and the N2 axis is
about 66. The average van derWaals 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.

Keywords: microwave spectroscopy, микроволновая спектроскопия, van der Waals complexes, ван-дер-ваальсовские комплексы, hyperfine structure, сверхтонкая структура