Abstract
The reaction between OH radicals and vibrationally excited CO molecules was studied directly in a fast flow discharge reactor. CO (v) molecules were produced by collision-induced vibrational energy transfer from nitrogen molecules vibrationally excited in a microwave discharge. Gas phase titration reactions were used to remove the nitrogen atom produced in the discharge. The vibrational and rotational temperature of CO (v) was determined using infrared resonance radiation from a cw-CO-laser for quantitative detection of CO (v=1,2,3,4) by absorption spectroscopy. The vibrational temperature Tv of the CO (v) molecules could be varied between 300 K≤Tv≤1800 K while the translational TT and rotational TR temperature remained at 298 K. A quadrupole mass filter coupled to the flow reactor by a nozzle beam sampling system was employed for quantitative detection of CO2 formed in the reaction CO(v)+OH→CO2+H The following rate constants were obtained: k1 (TT=TR=Tv=298 K)=(9.1±3.4·1010cm3 mol−1 s−1 K1 (TT=TR=298K,Tv=1400K)=(8.2±3.0)·1010 cm3 mol−1 s−1 K1 (TT=TR=298K,Tv=1800K)=(7.8±2.9)·1010 cm3 mol−1 s−1 Vibrational rate enhancement can therefore not be used to explain the substantial non-Arrhenius behavior observed for the thermal rate constant k1 (T). The results can be rationalized in terms of a reaction mechanism involving the formation of an intermediate complex.
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