Vibrational Excitation in ESCA and Soft X-ray Emission Spectra of Small Polyatomic Molecules

Abstract

The vibrational envelopes of the core ESCA bands of H2O and NH3 and of the 3a1 X-ray emission band of NH3 have been investigated by means of Franck-Condon analysis. The data for the equilibrium geometry and the force constants of the neutral ground, N1s and 3a1 ionized states of NH3 have been computed from ab initio wave functions, whereas the data for the neutral ground and the O1s state of H2O have been taken from literature [1]. The N1s state of NH3 is found to be planar with a significantly shortened N-H bond length in comparison with the neutral ground state. The ionization of the O1s state of H2O leads to an increase of the HOH angle by ∼ 16° with negligible change in the O-H bond distance. The vibrational intensities and energies computed from the ab initio results explain the band profiles of the spectra.