Dimethyl diazomalonate (1) was studied by laser flash photolysis (LFP) techniques. LFP of 1 generates dicarbomethoxycarbene (2), which can be intercepted with pyridine to give a UV-vis active ylide. Analysis of the yield of ylide as a function of pyridine concentration provides estimates of the carbene lifetime in various solvents, of its rate constant for Wolff rearrangement, of its reaction with various quenchers, and of intersystem crossing.