UV laser-induced photolysis of silacyclopent-3-ene in the gas phase is a clean extrusion of silylene yielding buta-1,3-diene. Silylene self-polymerisation and consequent deposition of Si n H 2 n agglomerates is precluded by concurrently occurring photolysis of buta-1,3-diene. The solid polymeric deposit being produced through polymerisation steps involving both H 2 Si: and the products of the buta-1,3-diene photolysis makes the reaction suitable for chemical vapour deposition of Si/C/H films.