Thermal rate constants of the complex-forming bimolecular reaction HO+CO■HOCO→H+CO2 were measured between 90 and 830 K in the bath gas He over the pressure range 1–700 bar. In addition, the vibrational relaxation of HO in collisions with CO was studied between 300 and 800 K. HO was generated by laser photolysis and monitored by saturated laser-induced fluorescence. The derived second-order rate coefficients showed a pronounced pressure and complicated non-Arrhenius temperature dependence. Above 650 K, the disappearance of HO followed a biexponential time law, indicating thermal instability of collisionally stabilized HOCO. By analyzing the corresponding results, an enthalpy of formation of HOCO of ΔHof,0=−(205±10) kJ mol−1 was derived. On the basis of energy- and angular-momentum-dependent rates of HOCO formation, activated complex properties for the addition reaction HO+CO→HOCO were derived from the limiting high-pressure rate constants; with the limiting low-pressure rate constants, activated complex properties for the dissociation HOCO→H+CO2 could be fitted as well. The observed transitions between low- and high-pressure limiting rate constants were well reproduced with these molecular parameters and collisional contributions; some evidence for rotational effects in collisional energy transfer was found. The surprisingly successful theoretical modeling of all available experimental data (80–2800 K, 0.0001–700 bar) allows for a satisfactory data representation of the rate coefficients over very wide ranges of conditions.
Saturated laser induced fluorescence is used for the sensitive detection of radicals in high pressure gases. The method and its application to a series of addition reactions of HO radicals in the high pressure regime are described. Experiments between 1 and 150 bar of the bath gas He allow for falloff extrapolations to the high pressure limit of the recombination reactions. Limiting rate constants (in cm3 molecule−1 s−1) of 2.2×10−11 for HO+HO→H2O2, of 3.3×10−11 for HO+NO→HONO, of 7.5×10−11 for HO+NO2→HONO2, and of 9.7×10−13 for HO+CO→HOCO (and H+CO2) are derived at 298 K.
The kinetics of the bimolecular reactions OH+C 2H2+M ... C 2H20H+M (I) and OH+C 2H4+M ... C 2H40H + M (2) have been investigated over an extended pressure (1-130 bar) and temperature (300-800 K) range. The OH radicals have been generated by laser flash photolysis of suited precursors and their decays have been measured by saturated laser-induced fluorescence (SLIF) under pseudo-first-order conditions. The pressure dependences have been analyzed by constructing falloff curves at fixed temperatures leading to reliable extrapolations towards the high pressure limiting rate constants k co' In the given temperature range these rate constants are represented as k l • co = 3.8xlO-11 exp(-910KIT)cm 3 molecule-I S-I and as k 2.co = 1.0xlO-11 em? molecule -I s -I . At temperatures above 700 K biexponential decay curves have been obtained. The chemical equilibria of reactions (1) and (2)
The recombination reactions HOϩNOϩM⇒HONOϩM͑1͒ and HOϩNO 2 ϩM⇒HNO 3 ϩM͑2͒ have been investigated over an extended pressure ͑1-1000 bar͒ and temperature ͑250-400 K͒ range. HO radicals were generated by laser flash photolysis of suitable precursors and their decays were monitored by saturated laser-induced fluorescence ͑SLIF͒ under pseudo-first-order conditions. The measured rate constants were analyzed by constructing falloff curves which provide the high pressure limiting rate constants k ϱ. In the given temperature range, these rate constants are k 1,ϱ ϭ(3.3Ϯ0.5)ϫ10 Ϫ11 ϫ(T/300 K) Ϫ(0.3Ϯ0.3) and k 2,ϱ ϭ(7.5Ϯ2.2)ϫ10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.