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Results obtained using nanosecond laser flash photolysis with various exitation wavelengths (337.1-600 nm) are reported for triplet-related properties of five aromatic thioketones, namely xanthione, thioxanthione, thiobenzophenone and p,p'-dimethoxy and p,p' -bis(N,Ndimethylamino) derivatives of thiobenzophenone. The triplet yields (&) of these thioketones in benzene are high (0.5-1.0) and show a dependence on excitation wavelengths. The intersystem-crossing efficiency is less than unity (0.5-0.6) when laser excitation is carried out into the second excited singlet state, S, (A,,= 355 and 425 nm), but approaches unity when the excitation leads to absorption into the lowest excited singlet, S1 (532 and 600 nm). The intrinsic triplet lifetimes are short (0.8-1.8 ps) and the self-quenching rate constants are in the range (2.6-7.1) X lo9 dm3 mol-' s-I. Quantitative data concerning triplet-triplet absorption spectra and triplet quenching by azulene, ferrocene, P-carotene and 2,5-dimethyl-2,4hexadiene are presented. The oxygen quenching rate constants [(2.8-9.7) X lo9 dm3 mol-I s-'1 increase when electron-donating groups (methoxy and N,N-dimethylamino) are present in the thiobenzophenones, suggesting that charge-transfer interaction i5 important. The efficiency of singlet-oxygen generation in the course of the oxygen quenching of the p,p' -dimethoxythiobenzophenone triplet is unity. The stable free radical, di-t-butylnitroxide, quenches the thioketone triplets with unusually high rate constants [( 1.4-3.3) X lo9 dm3 mol-1 s-l]; this behaviour appears to be a manifestation of electron-exchangemediated intersystem crossing (So 4-TI), enhanced by strong spin-orbit coupling or spin-spin interaction associated with the thiocarbonyl sulphur atom.

This report is one of a suite of products aiming to provide a consistent set of technology cost and performance data, and to define a scenario framework that can be used in forward-looking electricity analyses by the National Renewable Energy Laboratory's (NREL) and others. The long-term objective of this effort is to identify a range of possible futures for the U.S. electricity sector that illuminate specific energy system issues by (1) defining a set of prospective scenarios that bound ranges of technology, market, and policy assumptions and (2) assessing these scenarios in NREL's market models to understand the range of resulting outcomes, including energy technology deployment and production, energy prices, and carbon dioxide (CO2) emissions.This effort, supported by the U.S. Department of Energy's (DOE) Office of Energy Efficiency and Renewable Energy (EERE), focuses on the electric sector by creating a technology cost and performance database, defining scenarios, documenting associated assumptions, and generating results using NREL's Regional Energy Deployment Systems (ReEDS) and dGen models (see

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