X3Σg- → b1Σg+ 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.

Automated summary

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 using a liquid waveguide capillary cell. The results show that this weak near-infrared absorption transition can be investigated in common liquid hydrocarbon solvents, and heavy atoms have a significant effect on this spin-forbidden transition.