Vibrational treatment of hydroxylamine in valence coordinates.

A valence coordinate HNOH ground state potential energy surface accurate for all levels up to 6000 cm relative to trans zero point energy has been generated at the coupled-cluster single double triple-F12/aug-cc-pVTZ level encompassing the trans and cis as well as the N-H permutational conformers. All cis and trans fundamentals and a complete set of eigenfunctions up to about 3100 cm have been calculated and assigned using the improved relaxation method of the Heidelberg multi-configuration time-dependent Hartree package and an exact expression for the kinetic energy in valence coordinates generated by the TANA program. The average and maximal error to all observed transitions is about 6.3 and 14.6 cm, respectively. Local cis eigenfunctions exist with up to two quanta in the isomerization mode ν. Although no significant inversion splittings have been found up to the considered 3100 cm, they are expected within the fundamental energy range in view of the calculated 4261 cm H permutation/inversion barrier height. The cis-NH symmetric stretch fundamental shows a Fermi resonance with a splitting of about 10 cm.