This joint theoretical and experimental investigation focuses on the relative energetics and vibrational signatures of the azide-water (i.e., N3– and H2O) complex. Particular emphasis is placed on the O-H stretching region in order to compare theoretical results to those observed in the cryogenically cooled, messenger-tagged (H2) experimental spectrum afforded by mass-selected ion trap vibrational spectroscopy. The structures, energetics, and harmonic vibrational frequencies of binary azide-water (N3–/H2O) isomers are computed using MP2 and CCSD(T) in conjunction with a series of correlation consistent basis sets augmented with diffuse functions on all non-hydrogen atoms (i.e., cc-pVXZ for H and aug-cc-pVXZ for N, O, where X = T, Q). Preliminary DFT computations identified a Cs minimum energy structure exhibiting a single hydrogen bond and having a vibrational profile that is consistent with experiment. MP2 and CCSD(T) computations, on the other hand, reveal a C2v minimum energy structure, exhibiting two equivalent hydrogen bonds, as the only minimum (ni = 0). The only Cs stationary point resembling the DFT structure is a transition state (ni = 1) on the MP2 and CCSD(T) potential energy surfaces, a result that is not consistent with the free O-H stretch observed in experiment. To resolve this discrepancy, the present study examines the explicit inclusion of H2 to form ternary N3–/H2O/H2 complexes as well as the application of second-order vibrational perturbation theory (VPT2) to assess anharmonic effects including overtones and combination bands.

Probing the energetics and vibrational signatures of the azide-water complex

255th National Meeting (2018)

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