Abstract
C 2H 5CHO vapor was photolyzed with 313 nm radiation at 22 °C in the presence of O 2 and O 2He, O 2N 2, O 2NO and O 2 cis-2-C 4H 8 mixtures. The contents of the reaction mixture were allowed to bleed through a pinhole into a quadrupole mass spectrometer providing for continous monitoring of the C 2H 5OH and C 2H 5C(O)O 2H produced. CO, CO 2, C 2H 4 and CH 3CHO concentrations were determined by gas chromatography. From CO quantum yield determinations we found that the only photolytic process of importance is the following: ▪ The CO quantum yields also indicate that the reactive state of C 2H 5CHO is pressure quenched, and the half-quenching pressures for the various reactant gases were measured. The primary quantum yield in 1 atm of air is 0.30 ± 0.05. The data suggest that the reacting state is a vibrationally excited triplet state which consists of levels which are quenched with different efficiencies by any quenching gas. The more rapidly quenched leves account for about 40% of the total, while the less rapidly quenched levels account for about 60% of the total. Large quantum yields were measured for CO 2, C 2H 5OH and C 2H 5C(O)O 2H indicating a chain reaction initiated by abstraction of the aldehydic hydrogen of C 2H 5CHO by C 2H 5O radicals. The C 2H 4 quantum yields are dependent on the total pressure, and we believe that C 2H 4 is produced from the decomposition of vibrationally excited C 2H 5CO 3 radicals: ▪ The deactivated C 2H 5CO 3 radicals will either react with HO 2 or C 2H 5CHO or at the walls to produce C 2H 5CO 3H, or ultimately decompose to CO 2 + C 2H 5. We found that the following reactions are unimportant at 22 °C: ▪
Published Version
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