Experimental and Modelling Study of the Unimolecular Thermal Decompostion of CHF3

Abstract

Abstract The unimolecular thermal decomposition reaction CHF3 (+M)→CF2 + HF (+M) was studied in shock waves by monitoring the UV absorption of the forming CF2 radicals. The results of the present and previous experiments on the temperature and pressure dependence of the rate constants are analyzed in terms of unimolecular rate theory. Falloff curves (for 1500–1900 K) are represented in terms of fitted limiting low pressure rate constants k 0 = [Ar] 1.1 × 1016exp(−53.0 kcal mol−1/RT) cm3mol−1s−1, limiting high pressure rate constants k ∞ = 1.25 × 1015 exp(−75.8 kcal mol−1/RT) s−1 from quantum-chemical calculations, and center broadening factors F cent = 0.170(± 0.04) including strong and weak collision contributions from unimolecular rate theory. With these results, approximate analytical expressions of the falloff curves well represent the measured and calculated rate constants over wide ranges of pressure and temperature.