ISSN:
0538-8066
Schlagwort(e):
Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The kinetic isotope effect (KIE) for carbon and oxygen in the reaction CO + OH has been measured over a range of pressures of air and at 0.2 and 1.0 atm of oxygen, argon, and helium. The reaction was carried out with 21-86% conversion under static conditions, utilizing the photolysis of H2O2 as a source of OH radicals. The value of the KIE for carbon varies with pressure and the kind of ambient gas; for air the ratio of the reaction rates 12k/13k has the value 1.007 at 1.00 atm and decreases to 0.997 at 0.2 atm; for oxygen and argon over the same pressure range the values are 1.002-0.994 and 1.000-0.991, respectively. The value of the KIE for the CO oxygen atom is 16k/18k = 0.990 over the pressure range 0.2-1.0 atm and is independent of the kind of ambient gas. No exchange of the oxygen atoms in the activated complex, followed by decomposition to the starting molecules, was observed. From the mechanistic standpoint the normal KIE observed for carbon at the high pressure is attributed to the initial formation of the activated HOCO radical, whereas the inverse KIE observed at low pressures is a result of the KIE for the reverse reaction HOCO† → CO + OH being greater than that for the forward reaction HOCO† → CO2 + H. The derived isotopic equilibrium constant for HOCO ⇄CO favors the enrichment of 13C in the more strongly bound HOCO.
Zusätzliches Material:
5 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/kin.550121205
Permalink
