Estimation of thermal dissociation rate constant of CF3I to CF3 + I using laser absorption spectroscopy in a high repetition rate shock tube

Trifluoroiodomethane (CF3I) has gained attention as a potential fire suppressant due to its low environmental impact. It is considered as an alternative to fire suppressants containing bromine or chlorine, which have been phased out due to their detrimental effects on the ozone layer under the Montreal Protocol, signed in 1987. CF3I exhibits a low ozone depletion potential and is therefore considered a promising candidate for new fire suppression systems. This study focuses on investigating the thermal dissociation rate constant of CF3I to CF3 + I. In order to measure the thermal dissociation rate, the time resolved concentration of I was measured using laser absorption and developing a robust method for predicting rate constants using laser absorption spectroscopy in a shock tube. The experimental measurements encountered challenges due to the low signal strength caused by a short pathlength in the shock tube. Because the absorption of iodine is small and beam steering is large in the shock tube, different methods for ensemble averaging, and using a fixed wavelength double pass were used.To overcome this, a fixed wavelength double pass setup and a robust modeling technique were employed. To validate the procedure, eEthyl iodide (C2H5I) was initially also studied, and was used as a benchmark due to its well-known rate constant of thermal dissociation to C2H5 + I, ensuring to validate the correctness of the experimental and analytical approach. Subsequently, the study was extended to CF3I, as its the rate constant of the initial dissociation is not certain. The temperature range for the experiments was set between 1000-1500 K , covering the relevant thermal conditions. The obtained rate constant for CF3I is k(T)=10^27.67∙T^(-4.72)∙exp⁡(-11192/T) [ s^(-1) ] . Cantera, a chemical kinetics simulation software, was utilized to compare and validate the experimental results with models based on the rate constant values found in literature. Through this research, a comprehensive understanding of the thermal dissociation kinetics of CF3I is achieved. The developed method enables accurate prediction of rate constants, facilitating the evaluation and application of CF3I as a fire suppressant.