The rovibrational spectrum of hydroxylamine: A combined high resolution experimental and theoretical study

Abstract

This paper reports the rovibrational spectrum of hydroxylamine (NH2OH) recorded by interferometric Fourier transform spectroscopy with a resolution of up to 0.004 cm−1 close to the Doppler limit at room temperature, from 800 cm−1 up to the visible range of the spectrum. Detailed rotational analyses for 32 bands include all nine fundamentals and numerous overtones up to 10 500 cm−1. Approximate absolute band strengths, band centers and vibrational assignments are presented for a total of 72 bands up to the 4ν1 OH stretching overtone. The spectra are interpreted in terms of multidimensional vibrational calculations with potential and dipole surfaces constructed by multidimensional spline interpolation from more than 2×105 ab initioMP2/6-31G** points. The full three dimensional treatment of the torsion-inversion problem reveals well separated time scales for the two processes with a cis potential well supporting localized wave functions for the zero point and fundamental levels. Up to five dimensional normal coordinate models are employed for the analysis and dynamic interpretation of the complete vibrational spectrum up to 21 000 cm−1. Good quantitative agreement between observed spectra and results from ab initio calculations is obtained with a simple harmonic scaling procedure without any further empirical refinement. The comparison of various coupling schemes reveals an efficient path for the coupling between the OH and NH2 manifolds mediated through the OH bending mode. The implications for the effective homogeneous broadening at high energies are discussed.