Vibrational energy transfer in CO2–C2H2n+2 (n=0, 1, 2) mixtures from 220 to 300 K

Abstract

Time resolved laser induced infrared fluorescence studies have been performed to obtain the rate constants of energy transfer of CO2 (ν3) in mixtures with C2H2, C2H4, and C2H6 at temperatures between 220 and 300 K. A pulsed 10.6 μm CO2 laser light has been used to directly excite the CO2 molecules at low temperatures. The CO2 self-relaxation was measured and the results are in agreement with previous measurements. The rate constants for the transfer of energy in the CO2–C2H2 system show normal temperature behavior, (rate constant increases as the temperature increases) associated with large energy defect and caused by short-range repulsive forces. The rate constants for the systems CO2–C2H4 and CO2–C2H6 show an inverse temperature effect, (rate constant increases as the temperature decreases) associated with near resonant energy exchange and long-range attractive forces between the molecules. The observed behavior with temperature for the three systems is explained using a Morse potential which includes repulsive and attractive terms to describe the interaction between the molecules and a probability expression formulated by H. K. Shin, to calculate the energy transfer probabilities of some important reactions considered for each system.