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X 1027 exp(-10766 K/F) molecule cm"3 is obtained for the equilibrium CH300N02 " CH300 + N02. Some experiments were performed on the thermal decomposition of isomeric mixtures of butyl, hexyl, and octyl peroxynitrate at 253 K and in 800 mbar of N2. Atmospheric implications of the thermal stability of alkyl peroxynitrates are briefly discussed.

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The reactions of OH radicals with SO2, H 2 S, thiophenol, and a series of aliphatic thiols (1-5 C-atoms) have been investigated in 201 and 381 reaction chambers at 1 atm total pressure and 300 K using a competitive kinetic technique. Initially, OH radicals were produced by photolysis of CH3ONO/NO mixtures in air. Applying this OH source rate constants for OH with SO2, H2S , and thiophenol in synthetic air were determined to be (1.1-+0.2) x l0 -12, (5.5-+0.8) ×10 -12 and (1.1 +-0.2) × 10 -it cm 3 s -1 , respectively. However, when this method was applied to the aliphatic thiols the rate constants obtained were found to be dependent on the partial pressures of Oz and NO. These effects have been attributed to the built-up of a radical species, not yet identified, which leads to uncontrolled chain reactions in the system. Using the photolysis of H202 at wavelengths greater than 260 nm as the OH source in 1 atm N:, rate constants for the 1-5 aliphatic thiols in the range 2.9 to 5.6 × 10 -it cm 3 s -~ were obtained. The rate constants obtained in the present study are compared with recent literature values.

In flow tube studies of the quenching of 0 2 ( b ' Z i ) , broad band emission of Oz(b):M collision complexes was found to appear under the discrete rotational lines of the 0-0 band of the b'Cb -+ a'A, electric quadrupole transition at higher oxygen pressures and on addition of foreign gases. Bimolecular rate constants for the collision-induced emission processes have been derived from the ratio of the intensities of the discrete lines and the continuum as well as from lowresolution measurements of the relative intensities of the b + a and b + X bands as a function of 0 2 and added gas pressure. They range from S l O -" cm3 s-' for He to =4 X cm3 s-' for Pc13 vapor.

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