Anharmonic vibrational spectra of hydroxylamine and its 15N, 18O, and deuterium substituted analogs
1Institute of Inorganic Chemistry and Metallurgy of Rare Elements, Wrocław University of Technology, Poland. atk@ichn.ch.pwr.wroc.pl
Abstract:
Vibrational self-consistent field (VSCF) and correlation-corrected vibrational self-consistent field (CC-VSCF) methods were used to compute the anharmonic frequencies of fundamentals, overtones, and combination transitions of natural abundance hydroxylamine, 15NH2OH, NH2(18)OH, ND2OD, ND2OH, and NH2OD isotopomers at second order Møller-Plesset perturbation theory (MP2) in basis sets of triple-zeta quality. Frequencies of the fundamental transitions observed in the gas phase spectrum were reproduced by CC-VSCF treatment within 20 cm(-1) in TZV(d,p) and TZV(2d,2p) basis sets, and the change of basis set composition had only minor effect on the frequencies of the computed fundamentals. CC-VSCF computed wave numbers of overtone and combination transitions were typically within 1-40 cm(-1) of the gas phase band positions, except for those resulting from multiple excitations of v2, v3, and v7 fundamentals, because of a strong mutual coupling between these modes. Integral transition intensities calculated at MP2 level closely followed those of experimental spectrum, including intensity decrease in v1, 2v1, 3v1 progression, and 30-fold intensity increase of 2v8 in respect to that of v8 fundamental. The frequency of the OH torsional fundamental was found to be strongly dependent on the mode-mode interaction potential among v9 and v1, v7, v2, v4, v5 modes. Band shifts resulting from 15N, 18O and complete 2H substitutions were reproduced almost quantitatively by CC-VSCF computation in TZV(d,p) basis. Computed anharmonic isotope frequency shifts were different from those obtained in the harmonic approximation and no scaling procedure seemed capable of performing their interchange.
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