A Microwave Study of the Ammonia−Nitric Acid Complex

Microwave spectra of H 3 14 N−H 14 NO 3, H 3 15 N−H 14 NO 3, H 3 14 N−H 15 NO 3, and H 3 14 N−D 14 NO 3 have been obtained by Fourier transform spectroscopy in a supersonic jet. The spectra are consistent with a hydrogen-bonded structure having a planar arrangement of the heavy atom frame and a linear or near-linear hydrogen bond involving the HNO 3 proton and the lone pair on the ammonia. The hydrogen bond length obtained from the rotational constants is 1.736(63) Å and the nitrogen−nitrogen separation is 3.344(12) Å. The NO single bond of the nitric acid and the C 3 axis of the NH 3 form angles of 54(4)° and 21(3)°, respectively, with the line joining the centers of mass of the monomers. The hydrogen bond length is significantly shorter than that observed in related complexes such as H 3 N−HCl and H 3 N−HBr, indicating a particularly strong interaction between ammonia and nitric acid.