Infrared spectra and anharmonic coupling of proton-bound nitrogen dimers N-H-N, N-D-N, and N-H-N in solid para-hydrogen.

The proton-bound nitrogen dimer, N-H-N, and its isotopologues were investigated by means of vibrational spectroscopy. These species were produced upon electron bombardment of mixtures of N (or N) and para-hydrogen (p-H) or normal-D (n-D) during deposition at 3.2 K. Reduced-dimension anharmonic vibrational Schrödinger equations were constructed to account for the strong anharmonic effects in these protonated species. The fundamental lines of proton motions in N-H-N were observed at 715.0 (NHN antisymmetric stretch, ν), 1129.6 (NHN bend, ν), and 2352.7 (antisymmetric NN/NN stretch, ν) cm, in agreement with values of 763, 1144, and 2423 cm predicted with anharmonic calculations using the discrete-variable representation (DVR) method at the CCSD/aug-cc-pVDZ level. The lines at 1030.2 and 1395.5 cm were assigned to combination bands involving nν + ν (n = 1 and 2) according to theoretical calculations; ν is the NN stretching mode. For N-H-N in solid p-H, the corresponding major lines were observed at 710.0 (ν), 1016.7 (ν + ν), 1124.3 (ν), 1384.8 (2ν + ν), and 2274.9 (ν) cm. For N-D-N in solid n-D, the corresponding major lines were observed at 494.0 (ν), 840.7 (ν + ν), 825.5 (ν), and 2356.2 (ν) cm. In addition, two lines at 762.0 (weak) and 808.3 cm were tentatively assigned to be some modes of N-H-N perturbed or activated by a third N near the proton.