In experimental observations of the multiphoton decomposition of ethyl acetate by a CO 2 laser at 1045.0 cm −1 fluences up to 4 J cm −2 were employed to dissociate 2 Pa of ethyl acetate in up to 600 Pa of N 2, He, Ne, Ar, Kr, Xe, ethylene and acetone bath gases. The fraction dissociated was measured in a closed cell, either by rate of removal of reactant, monitored by a probe laser and spectrophone, or by rate of pressure rise, monitored by a capacitance manometer. Total absorption and transient absorption changes were also measured in separate experiments. Data were analysed by finite difference solution of the energy-grained master equation, incorporating collisional effects and changes in transitional temperature. The convergence of the solutions was checked with decrease in the size of the energy grain. Microscopic reaction rates were described by an RRKM formulation with parameters from thermal experiments. Radiation absorption was described by an energy-dependent cross section with one free parameter chosen to match independent data. The collisional energy transfer function was an exponential form with the mean down transfer energy <Δ E> as a parameter. Dissociation versus pressure and fluence was fitted by one value of <ΔE> for each bath gas: N 2-820, He-550, Ne-700, Ar-930, Kr-905, Xe-920, C 2H 4-3000, CO(CH 3) 2-5000 cm −1. The technique appears to be a reliable means of obtaining energy transfer data at low temperatures. In addition to the experiments with reactant diluted in bath gas, the decomposition of undiluted reactant was also observed, at pressures in the range 1 to 800 Pa; here, reaction was terminated by collisions of irradiated molecules with molecules outside the beam; an approximate theory which appears to confirm the hypotheses is presented.