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

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 Phi were found to be slightly dependent on the total pressure. At 100 Torr, Phi(100) = 0.36+/-0.03, whereas at 700 Torr the total quantum yield was Phi(700) = 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 + CH2=CHOH, having the absolute quantum yields of 0.031 and 0.118 at 700 Torr. The product CH2=CHOH tautomerizes to ethanal.