Photooxidation of n-heptanal in air: Norrish type I and II processes and quantum yield total pressure dependency

Abstract

Dilute mixtures of n-heptanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV lamps (275–380 nm) at 298 K. The main photooxidation products, identified and quantitatively analyzed by FTIR spectroscopy, were pent-1-ene, CO, vinyl alcohol and ethanal. The photolysis rates and the absolute quantum yields Φ were found to be slightly dependent on the total pressure. At 100 Torr, Φ₁₀₀ = 0.36 ± 0.03, whereas at 700 Torr the total quantum yield was Φ₇₀₀ = 0.31 ± 0.01. The results may be explained by the collisional deactivation of photoexcited molecules. Two decomposition channels were identified: the radical channel C₆H₁₃CHO → C₆H₁₃ + HCO, and the molecular channel C₆H₁₃CHO → C₅H₁₀ + CH₂CHOH, having the absolute quantum yields of 0.031 and 0.118 at 700 Torr. The product CH₂CHOH tautomerizes to ethanal.