A microwave study of the ammonia nitric acid complex

Microwave spectra of (H3N)-N-14-(HNO3)-N-14. (H3N)-N-15-(HNO3)-N-14, (H3N)- N-14-(HNO3)-N-15, and (H3N)-N-14-(DNO3)-N-14 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 HNO3 proton a nd the lone pair on the ammonia. The hydrogen bond length obtained from the rotational constants is 1.736(63) Angstrom and the nitrogen-nitrogen separ ation is 3.344(12) Angstrom. The NO single bond of the nitric acid and the C-3 axis of the NH3 form angles of 54(4)degrees and 21(3)degrees, respectiv ely, with the line joining the centers of mass of the monomers. The hydroge n bond length is significantly shorter than that observed in related comple xes such as H3N-HCl and H3N-HBr, indicating a particularly strong interacti on between ammonia and nitric acid.