Electronic structure of chromium oxides, CrOn− and CrOn (n=1–5) from photoelectron spectroscopy and density functional theory calculations

The electronic structure of CrOn− and CrOn (n=1–5) was investigated using anion photoelectron spectroscopy and density functional theory. Photoelectron spectra of CrOn− were obtained at several photon energies and yielded electron affinities, vibrational and electronic structure information about the neutral CrOn species. Density functional theory calculations were carried out for both the neutrals and anions and were used to interpret the experimental spectra. Several low-lying electronic states of CrO were observed and assigned from photodetachment of the CrO− ground state (6∑+) and an excited state (4∏), which is only 0.1 eV higher. The main spectral features of CrO2− were interpreted based on a C2v CrO2− (4B1). A very weak Cr(O2)− isomer was also observed with lower electron binding energies. Relatively simple and vibrationally resolved spectra were observed for CrO3−, which was determined to be D3h. The CrO3 neutral was calculated to be C3v with the Cr atom slightly out of the plane of the three O atoms. The spectrum of CrO4− revealed a very high electron binding energy. Several isomers of CrO4− were predicted and the ground state has a distorted tetrahedral structure (C2) without any O–O bonding. Only one stable structure was predicted for CrO5− with a superoxo O2 bonded to a C3v CrO3.