The Photolysis of Acetaldehyde Under Atmospheric Conditions

Abstract

The photodecomposition of mixtures of 100–200 ppm CrLCHO in 1 atm of air or purified N₂ has been studied at 300 K and the quantum yields of CO and CH, determined in the spectral range 250–340 nm. The quantum yields are nearly identical in both systems. ø_Co increases monoton-ically from zero at 330 nm to near 0.8 at 250 nm. ø_CH4 remains near zero at λ > 285 nm and increases sharply to 0.5 at 250 nm. A pressure dependence of ø_Co was observed at 313 nm, indicating that some quenching occurs. No H₂ was observed. Quantum yields for both primary steps

$$ C{H_{3}}CHO{\kern 1pt} \to {\kern 1pt} C{H_{3}} + CHO\quad {\phi _{1}} $$

$$ \to C{H_{4}} + CO\quad {\phi _{2}} $$

are derived. Measured CO production rates in sunlit CH₃CHO/Air and N₂ mixtures produce noontime dissociation rates of 3 × 10–⁶ sec^-1 at 30° zenith angle. This is a magnitude lower as the currently accepted vallue of Meafher et al. (1976)