Experimental studies of Cl-atom reactions at high temperatures: Cl+H2→HCl+H from 291 to 1283 K

Abstract

A method is presented for producing Cl atoms for kinetic experiments above 750 K. Combined with alow temperature Cl-atom production technique, rate coefficients for the title reaction have been obtained over a wide temperature range. The Cl atoms were generated by flash photolysis of CCl 4 for the lowtemperature measurements and by pulsed laser photolysis of NaCl for the high-temperature measurements. The relative Cl-atom concentrations were monitored by time-resolved resonance fluorescence. The data are well fitted by the expression k 1 (291–1283 K)=4.4×10 −11 exp(−2568 K/ T ) cm 3 molecule −1 s −1 , with 2σ precision limits of ±9 to ±16%, depending on temperature, and corresponding 2σ accuracy limits of about ±26%. There is good agreement between the rate coefficients measured here and those from previous low-temperature studies, leading to the recommendation k 1 (200–1283 K)=2.3×10 −16 ( T /K) 1.63 exp(−1592 K/ T ) cm 3 molecule −1 s −1 , with a suggested 2σ accuracy limit of ±28% for the combined data. A transition state theory calculation based on a semiempirical London-Eyring-Polanyi-Sato (LEPS) potential energy surface gives excellent agreement with the combined experimental results. Extension of our previous recommendation for the reverse reaction to lower temperatures leads to k 2 (200–1200 K)=6.6×10 −16 ( T /K) 1.44 exp(−1241 K/ T ) cm 3 molecule −1 s −1 , with 2σ accuracy limits within ±25%. There is excellent agreement between the present data and the predicted expression from that reaction and equilibrium data.