A Theoretical Investigation of the Renner Interactions and Magnetic Dipole Transitions in the ÖX̃ Electronic Band System of HO2

Abstract

The Ã2A′ → X̃2A" electronic band system of HO2 has been simulated in emission using an extended version of the program RENNER (P. Jensen, M. Brumm, W. P. Kraemer, and P. R. Bunker, J. Mol. Spectrosc. 171, 31–57 (1995)). The two electronic states involved in this transition have strongly bent equilibrium geometries but they correlate together to form a 2Π state at linearity. As a result the energy level pattern in the states is affected by electronic angular momentum effects (i.e., the Renner effect and spin–orbit coupling). To simulate the spectrum, we have calculated ab initio the potential energy surfaces, electric dipole moment surfaces, magnetic dipole moment surfaces, spin–orbit coupling parameter, and the electronic angular momentum matrix elements. Some of the forbidden ΔKa = 0 transitions occurring in the spectrum are induced by the magnetic dipole transition moment, and the others are electric dipole transitions that gain intensity because of the Renner interaction, spin–orbit coupling, or because of rotation–vibration interaction. All of these effects are allowed for in our calculation. The electric dipole transition moment is very small (0.017 D at the ground state equilibrium geometry) and because of this the magnetic dipole transitions are quite visible; the strongest magnetic dipole transitions are calculated to be about 10 times weaker than the strongest electric dipole transitions. In this way previous experimental assignments (E. H. Fink and D. A. Ramsay, J. Mol. Spectrosc. 185, 304–324 (1997)) are confirmed theoretically.