Shock tube studies of elementary hydroxyl-radical reactions important in combustion systems

The rate coefficients of the reactions{dollar}{dollar}rm CO + OH to COsb2 + Heqno(1)cr{dollar}{dollar}and {dollar}{dollar}rm HNCO + OH to rm Productseqno(2)cr{dollar}{dollar} were studied at high temperatures behind incident shock waves using non-intrusive cw laser absorption of the R{dollar}sb1{dollar}(5) line of the OH A{dollar}rmsp2Sigmasp+gets Xsp2Pisb{lcub}i{rcub}{dollar} (0,0) transition at 32606.56 cm{dollar}sp{lcub}-1{rcub}{dollar} (vacuum). Thermal decomposition of nitric acid (HNO{dollar}sb3{dollar}) vapor,{dollar}{dollar}rm HNOsb3 + M to OH + NOsb2 + M,eqno(3)cr{dollar}{dollar} was used as the source of OH radicals. The rate coefficients of these bimolecular reactions were determined via modeling of the observed OH time-histories. A fit to the measured rate coefficients led to the expressions(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) where the expression for k{dollar}sb2{dollar} incorporates the current work and the low-temperature data of other investigators.; The OH self reaction:{dollar}{dollar}rm OH + OH to Hsb2 O + Oeqno(4){dollar}{dollar} was investigated at elevated temperatures. The following expression for the rate coefficient was determined:{dollar}{dollar}rm ksb4{lcub}={rcub}9.40{lcub}times{rcub}10sp{lcub}-5{rcub} Tsp{lcub}4.77{rcub} exp({lcub}+{rcub}4570/Tlbrack Krbrack) lbrack cmsp3 molsp{lcub}-1{rcub} ssp{lcub}-1{rcub}rbrack.T {lcub}={rcub} 1050- 2380K{dollar}{dollar}; A quantitative CO{dollar}sb2{dollar} diagnostic based on narrow-line infrared absorption was developed using a lead-salt diode laser. Values for the collision-broadening parameter {dollar}rmgammasb{lcub}COsb2-Ar{rcub}{dollar} (HWHM) were determined at room and elevated temperatures for the R(48), R(50) and R(52) lines of the {dollar}(00sp01)gets(00sp00){dollar} band using rapid-scanning and fixed-frequency shock tube experiments. The following temperature-dependent expression was determined for the R(50) line at 2380.72 cm{dollar}rmsp{lcub}-1{rcub}{dollar}:{dollar}{dollar}{lcub}gammasb{lcub}COsb2-Ar{rcub}(T)overgammasb{lcub}COsb2-Ar{rcub}(Tsb{lcub}ref{rcub}){rcub}= left({lcub}Tover Tsb{lcub}rm ref{rcub}{rcub}right)sp{lcub}-0.61{rcub}.{dollar}{dollar} Here, T{dollar}rmsb{lcub}ref{rcub}=298{dollar} K and {dollar}rmgammasb{lcub}COsb2-Ar{rcub} (298 K)=0.0498 cmsp{lcub}-1{rcub} atmsp{lcub}-1{rcub}.{dollar}; The CO{dollar}sb2{dollar} diagnostic was applied to shock tube studies of the CO + OH reaction and the{dollar}{dollar}rm HNCO + OH to COsb2 + NHsb2eqno (rm 2a){dollar}{dollar}reaction. The rate coefficients for reaction (1) determined via the CO{dollar}sb2{dollar} diagnostic are in good agreement with those obtained using the OH diagnostic. The branching fraction for the CO{dollar}sb2{dollar} + NH{dollar}sb2{dollar} channel of reaction (2) was found to be independent of temperature, and equal to 5% for the temperature range 1250-1860 K.