Absorption Spectrum of Singlet Oxygen (aΔg→ b1Σg+) in D2O: Enabling the Test of a Model for the Effect of Solvent on Oxygen's Radiative Transitions

The time-resolved absorption spectrum of singlet molecular oxygen (a1Δg → b1Σg+) has been recorded in liquid D2O using a step-scan Fourier transform spectrometer. A molar absorption coefficient of 6 ± 2 M-1 cm-1 was determined for the peak of the absorption band at 5228 ± 6 cm-1. In this report, issues pertinent to the detection of this signal are outlined. Specifically, for O2(a1Δg) produced upon pulsed laser irradiation of a sensitizer, it is necessary to account for a laser-induced, temperature-dependent shift in a D2O absorption band that interferes with the weak a → b signal. Along with a → b absorption coefficients obtained previously in other solvents, the D2O data reported herein enable an appropriate test of a topical model for the perturbing effect of solvent on radiative transitions in oxygen.