The photo-oxidation of propionaldehyde
1982; Elsevier BV; Volume: 18; Issue: 2 Linguagem: Inglês
10.1016/0047-2670(82)80019-1
ISSN1873-2658
AutoresP. B. Shepson, Julian Heicklen,
Tópico(s)Atmospheric chemistry and aerosols
ResumoC2H5CHO vapor was photolyzed with 313 nm radiation at 22 °C in the presence of O2 and O2He, O2N2, O2NO and O2cis-2-C4H8 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 C2H5OH and C2H5C(O)O2H produced. CO, CO2, C2H4 and CH3CHO 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 C2H5CHO 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 CO2, C2H5OH and C2H5C(O)O2H indicating a chain reaction initiated by abstraction of the aldehydic hydrogen of C2H5CHO by C2H5O radicals. The C2H4 quantum yields are dependent on the total pressure, and we believe that C2H4 is produced from the decomposition of vibrationally excited C2H5CO3 radicals: The deactivated C2H5CO3 radicals will either react with HO2 or C2H5CHO or at the walls to produce C2H5CO3H, or ultimately decompose to CO2 + C2H5. We found that the following reactions are unimportant at 22 °C:
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