Theoretical studies of valence-shell photoexcitation and ionization cross sections in nitric oxide

Abstract

Theoretical studies in static-exchange approximation are reported of photoexcitation and partial-channel photoionization cross sections of the outer-valence-shell 2π, 1π, 5σ, and 4σ electrons in nitric oxide. The calculations account satisfactorily for observed Rydberg series and for the spectral shapes of corresponding experimental photoionization cross sections. Multiplet-specific static-exchange potentials are employed for construction of 2π −1, 5σ −1, and 4σ −1 excitation series and partial cross sections. These are required particularly for (5σ −1)b 3 Π and (5σ −1)A 1Π partials in order to obtain values in agreement with recent synchrotron-radiation studies, which exhibit resonance maxima having different kinetic energies in the two channels. Additionally, the multiplet-specific calculations predict triplet-singlet cross sectional maxima in the 5σ −1 channels that differ noticeably from a statistical 3:1 ratio, also in good accord with measured values. Slater-average potentials are employed for the many channels that arise from 1π ionization, providing results in generally good agreement with dipole (e, 2e) measurements. Good agreement also obtains between measured values and the calculated 2π and 4σ cross sections, the present results thereby providing an overall clarification of the partial-channel photoionization cross sections of NO. Stieltjes orbitals in body-frame point-group symmetry provide three-dimensional graphical diagnostics of various resonance features present in the photoionization cross sections. The 6σ(σ*) antibonding orbital is found merged in kσ final-state continua, accounting for the presence of strong photoionization resonance features, and for the absence of corresponding discrete excitations. Computational aspects of the construction of Stieltjes cross sections and orbitals are discussed, and the origins of apparent discrepancies among calculated NO partials in the literature are clarified.