X-3 Sigma(-)(g) -> b(1)Sigma(+)(g) Absorption Spectra of Molecular Oxygen in Liquid Organic Solvents at Atmospheric Pressure

Spectra and absorption coefficients of the forbidden 765 nm X-3 Sigma(-)(g) -> b(1)Sigma(+)(g) transition of molecular oxygen dissolved in organic solvents at atmospheric pressure were recorded over a 5 m path length using a liquid waveguide capillary cell. The results show that it is possible to investigate this weak near-infrared absorption transition in a common liquid hydrocarbon solvent without the need for a potentially dangerous high oxygen pressure. Proof-ofprinciple data from benzene, toluene, chlorobenzene, bromobenzene, and iodobenzene reveal a pronounced heavy atom effect on this spin-forbidden transition. For example, the absorption coefficient at the band maximum in iodobenzene, (28.9 +/- 3.3) X 10(-3) M-1 cm(-1), is approximately 21 times larger than that in benzene, (1.4 +/- 0.1) x 10(-3) M(-1)( )cm(-1). These absorption measurements corroborate results obtained from O-2 (X-3 Sigma(-)(g)) -> O-2 (b(1)Sigma(+)(g)) excitation spectra of O-2 (a(1)Delta(g) ) -> O-2(X-3 Sigma(-)(g)) phosphorescence, which depended on data from a plethora of convoluted experiments. Spectroscopic studies of molecular oxygen in liquid solvents can help evaluate aspects of the seminal Strickler-Berg approach to treat the effect of solvent on Einstein's A and B coefficients for radiative transitions. In particular, our present results are a key step toward using the O-2(X-3 Sigma(-)(g)) -> O-2(b(1)Sigma(+)(g)) transition to evaluate the speculated limiting condition of applying the Strickler-Berg treatment to a highly forbidden process. This latter issue is but one example of how an arguably simple homonuclear diatomic molecule continues to aid the scientific community by providing fundamental physical insight.