Propane has been photolyzed at 123.6 nm, in the presence and absence of O2, at pressures from 2–380 Torr. All products except ethane exhibit a pressure dependence which is attributed to secondary dissociation of the primary fragments, H2, CH4, C2H4, and C3H6. It is assumed that the range of energies carried by these fragments is broad enough that some will not dissociate even at low pressures while others of the same species cannot be stabilized even at high pressures. An internally consistent analysis rationalizes the entire observed product spectrum, with some uncertainty arising from an ambiguity in the source of acetylene. The following primary quantum yields, prior to secondary dissociation, are estimated:
C3H8 + hv = H2 + C3H6 φ = 0.42 mol/einstein
= C2H4 + CH4 φ = 0.47 mol/einstein
= CH2 + C2H6 φ = 0.09 mol/einstein



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