A. GANDINI, J. M. PARSONS: and R. A. BACK. Can. J. Chem. 54, 3095 (1976). The photolysis of furaldehyde vapour at 253.7 nm, 65 "C, and pressures from about 0.2 to 7 torr, produces CO, propyne, allene, furan, cyclopropene, COP, and CzHz. The quantum yield of CO approaches 2 at low pressure and decreases towards zero with increasing pressure of furaldehyde or added C02. Yields of the other products also decrease but show a more complex pressure dependence. A mechanism involving excited furaldehyde and excited C4H40 and C3H4 intermediates is suggested.The Hg(3PI)-photosensitized decomposition gives products very similar to those of the direct photolysis. Photolysis at 313 and 366 nm also leads to similar products but in much lower yields, with the major product, CO, having a quantum yield of about 0.01. Some photopolymerization was observed in all systems.A. GANDINI, J. M. PARSONS et R . A. BACK. Can. J. Chem. 54, 3095 (1976).La photolyse du 2-furfural en phase vapeur B 253.7 nm et 65 "C dans le rang de pression 0.2-7 torr produit CO, propyne, allbne, furanne, cyclopropkne, CO2 et CzH2. Le rendement quantique en CO tend B 2 aux faibles pressions et decroit vers zero quand on augmente la pression de furfural ou on ajoute COP. Les rendements des autres produits decroissent aussi mais leur comportement en fonction de la pression est plus complexe. On propose un mecanisme base sur la formation d'intermkdiares excitks du furfural, du C4H40 et du CjH,.La dCcomposition photosensibilizCe au Hg(3PI) montre un comporternent tres semblable B celui de la photolyse directe. La photolyse B 313 et 366 nm donne aussi les m&mes produits mais avec des rendements beaucoup plus faibles; le rendement du produit plus important, CO, est d'environ 0.01. Dans tous les systemes on observe de la photopolymerization.