O-2(a(1)Delta(g)) absorption and O-2(b(1)Sigma(+)(g)) emission in solution: Quantifying the a-b Stokes shift

TitleO-2(a(1)Delta(g)) absorption and O-2(b(1)Sigma(+)(g)) emission in solution: Quantifying the a-b Stokes shift
Publication TypeJournal Article
Year of Publication2000
AuthorsKeszthelyi, T, Poulsen, TD, Ogilby, PR, Mikkelsen, KV
JournalJournal of Physical Chemistry A
Date Publishednov

In a nanosecond time-resolved infrared spectroscopic study of dissolved oxygen, O-2(a(1)Delta (g)) absorption, i.e., a(1)Delta (g) –> b(1)Sigma (+)(g), and O-2(b(1)Sigma (+)(g)) emission, i.e., b(1)Sigma (+)(g) –> a(1)Delta (g), were monitored at similar to 5200 cm(-1) in a number of solvents. The maxima of the respective spectra depend significantly on the solvent, indicating that the O-2(a(1)Delta (g)) and O-2(b(1)Sigma (+)(g)) energy levels likewise depend significantly on the solvent. The corresponding Stokes shifts, however, are small. The latter, recorded as the difference between the absorption and emission maxima, do not exceed the uncertainty limits that derive from the step-scan Fourier transform spectroscopic measurements (similar to+/-13 cm(-1)). Nevertheless, the data clearly indicate that the difference between the equilibrium and nonequilibrium solvation energies for the O-2(a(1)Delta (g)) and O-2(b(1)Sigma (+)(g)) states is not large. Within the error limits, it is not possible to ascertain if the Stokes shifts are solvent dependent. Ab initio computational methods were used to model the data, and the results indicate that both long- and short-range interactions between oxygen and the perturbing solvent must be considered to adequately describe spectroscopic transitions in dissolved oxygen. The computational results indicate that a 1:1 complex between oxygen and the perturbing molecule embedded in a dielectric continuum appears to provide a sufficiently accurate model that can be used to probe subtle solvent-oxygen interactions.