Calculation of the electronic and photoelectronic spectra of nitroso compounds: a reinvestigation by use of configuration interaction methods

Abstract

The electronic properties of three selected nitroso compounds: nitrosyl chloride (NOCl), nitrosomethane (CH 3NO) and trichloronitrosomethane (CCl 3NO) have been compared, and their UV and photoelectron spectra calculated within an extensive configuration interaction treatment. Triple ζ Dunning basis set for NOCl and pseudo potentials basis sets for CX 3NO, complemented with Rydberg orbitals for the calculation of the UV spectrum have been used. The visible band of the UV spectra of the three compounds is attributed to a 1A ″ state: it is a triplet state for NOCl due to spin–orbit splitting, and a singlet state for the two other compounds. In the case of NOCl and CH 3NO, some Rydberg orbitals are involved in the short wavelengths transitions. However, the corresponding band is poorly resolved in the case of NOCl and not recorded in this region for CH 3NO. For CCl 3NO, the UV spectrum is much simpler. For the photoelectronic spectra of the three compounds, the presence of a low-lying unoccupied orbital located on π ∗ z( NO) induces some defect to Koopmans’ theorem and to the one-particle model of ionization. These results imply that the experimental spectrum of NOCl has to be reassigned in this scheme.