Matrix-isolated oxygen: Line-shapes and transition probabilities of the b 1∑ g+→X 3∑ g−, b 1∑ g+→a 1Δg and a 1Δg→X 3∑ g− transitions

Abstract

The b 1∑ g +↔X 3∑ g −, b 1∑ g +→a 1 Δ g and a 1 Δ g→X 3∑ g − transitions of molecular oxygen isolated in Xe, Kr, Ar (2 sites) and Ne matrices have been studied in excitation and emission. The radiative lifetimes of the isolated monomers in these matrices are 9.5 ± 0.3, 14.5 ± 0.5, 24.5 ± 1 and 46 ± 1 ms in the b state, and 11.5 ± 0.5, 34 ± 1, 68 ± 2 and 146 ± 3 s in the a state. The vibrational relaxation rates of the a, ν′ = 1, level amount to 0.21, 0.18, 0.15 and ≥0.14 s −1. Dimers or otherwise perturbed oxygen molecules with shorter lifetimes have also been characterized. Relative intensity measurements of the involved electronic transitions show that the b→a and a→X radiative transition probabilities are enhanced up to four orders of magnitude due to a phonon-induced transition dipole moment, giving rise to intense phonon sidebands with similar local mode structure in both transitions. While the enhancement of the a→X transition is probability attributed to intensity borrowing from the b→a transition, the b→X transition is only mildly affected by the matrix. The ratio A b→a: A a→X of the Einstein coefficients for spontaneous emission in matrices compares well with the reported ratio for O 2 in CCl 4 solution, supporting the intensity borrowing mechanism.