Experimental and theoretical studies of rate coefficients for the reaction 0(~3P)+CH_3OH at high temperatures

摘要

Rate coefficients of the reaction O(~3P)+CH_3OH in the temperature range of 835-1777 K were determined using a diaphragmless shock tube.O atoms were generated by photolysis of SO_2 with a KrF excimer laser at 248 nm or an ArF excimer laser at 193 nm;their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O_2 and He.The rate coefficients determined for the temperature range can be represented by the Arrhenius equation,kappa(T)=(2.29+-0.18)X 10~(-10) exp[-(4210+-100)/T] cm~3 molecule~(-1) s~(-1);unless otherwise noted,all the listed errors represent one standard deviation in fitting.Combination of these and previous data at lower temperature shows a non-Arrhenius behavior described as the three-parameter equation,kappa(T)=(2.74+-0.07)X10~(-18)T~(2.25+-0.13) exp[-(1500+-90)/T] cm~3 molecule~(-1) s~(-1).Theoretical calculations at the Becke-3-Lee-Yang-Parr (B3LYP)/6-311+G(3df,2p) level locate three transition states.Based on the energies computed with coupled clusters singles,doubles (triples) [CCSD(T)]/6-311+G(3df,2p)//B3LYP/6-311+G(3df,2p),the rate coefficients predicted with canonical variational transition state theory with small curvature tunneling corrections agree satisfactorily with the experimental observations.The branching ratios of two accessible reaction channels forming OH+CH_2OH (la) and OH+CH_3O (1b) are predicted to vary strongly with temperature.At 300 K,reaction (la) dominates,whereas reaction (1b) becomes more important than reaction (la) above 1700 K.