Solvent induced emission of molecular 1Δg oxygen

Abstract

Intensities of a1Δg−X3Σg− and b1Σg−−X3Σg− transitions in an isolated O2, molecule have been calculated on the basis of the MINDO/3 CI method taking into account spin-orbit coupling (SOC) by perturbation theory. The same method has been used for analysis of the Herzberg I–III and Chamberlain-Slanger bands. In the molecule the a−X and b−X transitions are magnetic dipoles in nature, but in collision complexes of O2 with solvent molecules (H2O, NH3, N2, C2H4, C10H8, CH3X, where X = F, Cl, Br) the a−X and a−b transitions acquire an electric-dipole character. The complexes have been calculated by the MINDO/3 CI method including double and single excited configurations. The main SOC channel of b−X mixing in O2 moiety in collision complexes and the comparatively large a−b transition electric-dipole moment lead to intensity enhancement of the a−X transition in solutions. The induced electric-dipole moment of the a−X transition strongly depends on the intermolecular distance R in the collision complex O2+XCH3. The CX valence bond stretching vibration is able to modulate the R value. In this way it is possible to explain a new type of singlet oxygen emission, induced by solvent and displaced to the longer wavelength having value ωC−X⋍600 cm−1.