Direct irradiation of ((trimethylsilyl)ethynyl)pentamethyldisilane in hydrocarbon solution affords a mixture of reactive intermediates which have been detected and identified using laser flash photolysis techniques and trapped as the methanol adducts in steady state irradiation experiments, Flash photolysis of air-saturated hexane solutions of the disilane allows detection of transient species assigned to 1,1-dimethyl-3,3-bis(trimethylsilyl)-1-silaallene and dimethylsilylene, along with a non-decaying species assigned to 1,1-dimethyl-2,3-bis(trimethylsilyl)-1-silacyclopropene, These were identified on the basis of their UV absorption spectra and reactivity toward various reagents, The 1-silaallene is a minor photoproduct, but it is readily observable in transient absorption experiments because it is relatively long-lived (tau 2.4 mu s in air-saturated solution) and absorbs strongly, with absorption maxima considerably to the red of those of the 1-silacyclopropene, The 1-silaallene exhibits characteristic silene reactivity; it reacts with methanol, acetic acid, acetone (k = 10(6)-10(8) M(-1) s(-1)) and oxygen (k similar to 10(8) M(-1) s(-1)), exhibits low reactivity toward aliphatic dienes and tert-butyl alcohol, and decays with second-order kinetics in the absence of quenchers, With methanol and acetic acid, it has been shown that reaction in hexane occurs with the monomeric ROH species only. Steady state irradiations in the presence of methanol afford methanol-addition products consistent with the formation of the silaallene, silacyclopropene, and silylene, along with bis(trimethylsilyl)acetyiene as the major product.