The synthesis of the azoalkane precursor 21 was accomplished through a Diels-Alder route. This precursor provided a clean and convenient source of the 1,3-biradical 13 upon photolysis. Determination of the product ratio from the triplet biradical by gas chromatographic analysis yielded the rate of intersystem crossing of the biradical from the triplet to the singlet energy state. Structure confirmation of the cyclopropyl ring opening product was accomplished through co-injections of photolysis product and an authentic sample on two different GC columns. The lifetime of 13T was found to lie in the range of 0.4 ns to 18 ns. Comparison of this value to that of 6, whose lifetime is 59 ns, confirms that gem-dimethyls have the effect of increasing the intersystem crossing rate.