C-13-Selective infrared multiple photon decomposition of lactone compounds has been studied using a CO2 TEA (transversely excited atmospheric) laser. The main decomposition products were ethylene and CO2 in beta-propiolactone, We obtained CO2 with a C-13 atomic fraction of 55% in the irradiation of 2 Torr (1 Torr = 1 mmHg = 133.322 Pa) beta-propiolactone at 1035.47 cm(-1). The addition of 100 Torr of N-2 to 2 Torr of beta-propiolactone resulted in a remarkable increase in selectivity, i.e., 75% C-13 in CO2, while the yield was considerably decreased. Respective olefinic products were propylene and allene in the multiple photon decompositions of beta-butyrolactone and diketene. The common product CO2 was also found to be significantly enriched with C-13 in these lactone compounds.