La photolyse du butyne-1 a t t e observke a 147, 163 et 174 nm. Les principaux produits C, a C, ont ete mesurks dans le monomere pur ou en presence d'additifs et a differentes pressions (0,5 a 100 Torr -65 a 13 300 N m-2). Le radical rn6thyle est I'espece intermediaire dont le rendement est le plus important. L'acetylkne, I'ethylene et le vinylac6tylene sont produits en presence d'intercepteur radicalaire et proviennent probablement de la fragmentation de la moleculephotoexcit6e. On a note en outre une forte polym6risation mkme en presence d'intercepteur radicalaire, et la presque impossibiliti d'intercepter les radicaux C,H, par I'iodure d'hydrogene. Des reactions secondaires diverses interviennent tres certainement et compliquent I'interpretation. Par exemple I'augmentation du rendement en ethylene sur addition d'oxygene est difficilement explicable sur la notion simple habituellement admise de I'interception des radicaux libres par cet additif. H~L P N E DESLAURIERS, JOVETTE DESCH~NES, and GUY J. COLLIN. Can. J. Chem. 58,2100(1980). We have studied the 147, 163, and 174 nm photolysis of I-butyne. Several products from C, to C, were observed under various conditions such as in the presence of additives, or at different pressures between 0.5 and 100 Torr (65 to 13 300 N m-2). The methyl radical is the most important radical intermediate. Acetylene, ethylene, and vinylacetylene are produced in the presence of radical scavengers and are probably the result of the fragmentation of the photoexcited molecule. Propargyl radicals are thought to be produced but appear not to be scavenged by hydrogen iodide. Polymerization was observed even in the presence of radical scavengers. Secondary processes are numerous and make the interpretation of our results difficult; for example, the ethylene quantum yield increased upon addition of 10% oxygen, the simple radical scavenging effect of this additive does not explain such an effect.