Theoretical study of excitation and radiative de-excitation characteristics for the NO molecule

Soft x-ray emission spectra of the open shell NO molecule are simulated using multiconfiguration self-consistent field ab initio calculations with an extensive triple zeta atomic natural orbital basis set. All states involved in the spectral simulation are optimized individually for their minimal energy geometries. The valence-ionized states with open shells (both the singlet and the triplet) exhibit longer N-O bond lengths than the neutral NO ground electronic state; whereas the closed shell valence-ionized state of X (1)Sigma(+) has the shortest bond length among the states involved. For the core-ionized states, however, the calculations indicate the lengthening of the N-O bond for core ionizations centred on the oxygen atom but contraction for the ionizations centred on nitrogen. Nuclear dynamics has been applied to the spectral simulations in order to construct the vibrational envelope associated with the x-ray emission processes. The simulated O-K and N-K spectra of NO agree well with the available experiment. The characteristics of the potential energy surfaces of the N1s and O1s core states explain the differences in the O-K and N-K emission spectra of NO.