Time-resolved infrared diode laser spectroscopy for the study of chemical reactions is described in this review article. The diode laser has wide applicability for monitoring molecules in the gas phase and also measuring detailed energy distributions in the molecules, because of high selectively, originating from its narrow bandwidth (≈ 10^-4 cm^-1), and wide coverage of the infrared region (300-3600 cm^-1). We combined this spectroscopic method with infrared multiphoton decomposition (IRMPD) induced by CO₂ laser irradiation for the first time, and investigated elementary reactions of CF₃, CF₂ and SiH₃ radicals with small molecules and those of F atoms with CH₄ and CH₃I. The CF₃ and CF₂ were produced by the IRMPD of CF₃I and CHCIF_2, respectively, while the SiH₃ radicals were produced by the reaction of SiH₄ with Cl atoms, generated by the IRMPD of CCI₃F. The concentrations of the radicals and reaction products were monitored as a function of time after the CO₂ laser pulse. Rate constants for the above reactions were determined and the reaction mechanism was discussed. This technique was utilized to observe energy distributions of CH₃ radicals produced in the reactions F + CH₄ and F + CH₃l. The F atoms were produced by the IRMPD of SF₆. From the energy distributions in the products the dynamics of the reactions were discussed.