Quantum yields of CO and of H2have been measured in the gashyphen;phase photolysis with 4358hyphen;Aring; radiation at temperatures between 37deg; and 207deg;C. phgr;COis generally about 0.6; phgr;H2is about 0.01. The data suggest that about 70 of the excited molecules cross to the triplet state by a firsthyphen;order process, and the remaining excited singlet molecules return to the ground state with fluorescence. The principal reaction of triplet molecules is a dissociation into CO and HCHO, while a small fraction of triplet molecules are destroyed by collision with groundhyphen;state glyoxal molecules. About 3 of the triplet molecules undergo a firsthyphen;order intersystem crossing to the ground state, forming molecules with about 55 kcal of vibrational energy. These either dissociate into H2and CO or relax to vibrational equilibrium by collision with heathyphen;bath molecules. At pressures near 100 Torr, where higher concentrations of triplet molecules are formed because of increased absorption, reactions of free radicals produced in collisions between triplet molecules also contribute significantly to phgr;H2. The data suggest that temperature variation has little effect on the reactions destroying the triplet state, but that the rate of vibrational relaxation in the ground state increases markedly at higher temperatures.
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