The non-linear optics basis and experimental realization of time-resolved IR spectral photography (TRISP), a new technique of nanosecond time-resolved IR absorption spectroscopy, are described. TRISP has been applied to the study of transients. It was used to study the time evolution of the rotational temperature of HCI during CO2-laser-induced explosions of HN3-HCI mixtures. In a recent experiment tert-butyl radicals were formed by ruby laser photolysis of (CH3)3CNO. TRISP was used to obtain the gas phase IR spectrum of the radicals in the 3 μm region. By following the decay of this transient IR absorption, the rate coefficients for the combination and disproportionation reactions between tert-butyl radicals were deduced. © 1981.