Abstract
Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen (1Δg and 1Σg+) were calculated for a number of conditions. For the gas phase we estimate Keq(1Δg3Σg‐) = 1.67 exp(‐94.31 KJ/RT) and Keq(1Σg+/3Σg‐) = 0.33 exp(‐157.0 KJ/RT). The calculated rate constants for the 3Σg+→1Δg transition of O2 at 25°C varied from 2.5 × 10‐11 s‐1 in water to 4.8 × 10‐16 s‐1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro‐oxidant effect.
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