The technique with inclusion of overlap charges, as described in previous papers of this series, has been extended to evaluate the -bond energies, heats of formation, and resonance energies of some conjugated hydrocarbons. The success of the method has been supported by comparing the results with experimental data and with results obtained by others using Pople's SCF-MO method.

The flash photolysis of N02ions in aqueous solution gives rise to three transient absorptions assigned to N02 (Xmax ~400 nm), N204 (Xmax ~340 nm), and N203 (Xmax <250 nm). The formation of Or in air-saturated alkaline solutions of nitrite ions, and of Br2~and C03 ~radicals in the presence of Br~and C032ions, indicates that O-(or OH) radicals are produced by the primary photolytic process NOr + hv~* NO + O-. The mechanism proposed for the generation of the other nitrogen oxides, 0

The photochemistry of aqueous 9,10-anthraquinone-2-sulfonate (AQS) was investigated by using four different approaches: (1) laser photolysis of AQS in water as a function of concentration and pH; (2) laser photolysis of AQS in CH3CN and CH3CN/H20 mixtures, combined with emission spectroscopy; (3) steady-state photolytic study of the effect of AQS concentration and pH on the yield of photohydroxylation in water; (4) quenching of intermediates and inhibition of photohydroxylation by inorganic anions. Our results lead to identification of triplet AQS ( ~100 ns in water) and two other intermediates (B and C) which are formed by two parallel reactions of triplet AQS with H20. The nature of these intermediates is still uncertain, but evidence is presented to rule out H abstraction or net electron transfer (even in the case of OH") leading to formation of free OH radicals. The possibility that B and C are two different water adducts is discussed. The role of preferential solvation of AQS in CH3CN/H20 mixtures in determining its photochemistry is also examined. Species C (Xmax ~600 nm) is the only transient observed which appears to react with ground-state AQS, and this reaction is considered to be responsible for photohydroxylation. Our results provide direct evidence for the validity of the "3AQS/H20" mechanism proposed by Clark and Stonehill (CS), in which the primary step is reaction of 3AQS with water (and not with ground-state AQS) to produce the hydroxylating agent. However, this mechanism is modified for pH 511 by proposing another hydroxylating agent which may be AQS"OH exciplex (or radical pair) produced by charge-transfer (CT) quenching of 3AQS by OH". Evidence is presented to establish the charge-transfer nature of quenching of triplet AQS by various anions including OH". ACO2-76ER03117).Registry No. 9,10-Anthraquinone-2-sulfonate, 84-48-0.

No abstract

The interaction between triplet benzophenone-4-carboxylate (3BC) and some inorganic anions, X", has been studied by laser flash photolysis over a wide range of anion concentration (up to 6 M), at pH 11 and constant ionic strength. Spectra and extinction coefficients of 3BC and BC1 89" radical were determined by using the benzophenone actinometer. Triplet lifetime measurements gave primary interaction rate constants, kf-(M_1 s'1), close to diffusion controlled for iodide, thiocyanate, and azide (k ~2 X 12109), somewhat less for bromide (2 X 108) and very low for chloride (<106). Radical yields, 0.1 M, <¿-r increases with [X"] and equivalent amounts of BC'" and X2" radicals are formed, including N6~. At high anion concentrations, plots of versus [X"]"1 are linear. Limiting