The following were identified as secondary products of the mercury-photosensitized decomposition of neopentane, and their maximal rates measured over a range of conditions: C2H4, C3H6, C3H8,i-C4H10, 2,2,3,3-tetramethylbutane, and 2,2,4,4-tetramethylpentane. A mechanism is proposed which explains the kinetics of formation of these products. It involves the reaction of H atom withi-C4H8formed as a primary product; this leads to the formation of C4H9which reacts further; one of its products is C3H6which also reacts with H atoms.