2974
. I Phys. . Chem. 1988, 92, 2914-2918
indeed C H 2 0 + OH are the dominant products of the CH3 + O2 reaction below 2800 K. We are unable to explain the remaining discrepancies with some of the former results. It should be noted though that the recent work of Saito et al.” casts some doubt on the earlier results of Baldwin and Golden,’* who failed to observe a reaction between CH3 and O2 in a VLPP experiment at 1220 K and which has frequently been taken as reliable evidence against a low activation energy reaction channel between these reagents. Although the experiments of ref 11 and 12 do not overlap in temperature range, the extrapolation of the data of ref 11 to 1200 K indicates a discrepancy by a factor of about 30. Since it is difficult to reconcile this difference on the basis of CH302complex formation, further experimental verification in this temperature regime is clearly necessary. At the time when the present work was submitted we became aware of a similar computational study of the C H 3 O2 hightemperature reaction by Dean and Westmoreland.15 These authors used quantum R R K theory (QRRK), a simplified version of RRKM theory which makes use of only one (estimated) geometric mean frequency of the activated complex, rather than a full frequency spectrum as in RRKM theory. The result for channel l a is within a factor of 2 with the present prediction. for channel 1b, however, the isomerization barrier between CH3O2 and
-
+
C H 2 0 0 H was treated as a variable such that no conclusive evidence in support or rejection of this channel could be obtained.
Conclusion The present work provides evidence for the existence of a low activation energy channel of the C H 3 + O2 high-temperature reaction with C H 2 0 + OH as products. Contrary to most previous assumptions, this channel is predicted to dominate over the alternative C H 3 0 + 0 channel at all temperatures below 2800 K. The present result is based purely on computation. The required input parameters, however, are based on previous experimental studies on the low-temperature C H 3 0 + 0 reaction and hence are devoid of larger adjustments. Experimental confirmation of our predictions in the temperature range 1000-1200 K is called for. Acknowledgment. Support of this work by “Deutsche Forschungsgemeinschaft (DFG)”, “Fonds der Chemischen Industrie”, and the Commission of the European Community (nonnuclear R & D program) is gratefully acknowledged. R.Z. also thanks DFG for a “Heisenberg-Stipendium”. Registry No. CH,, 2229-07-4;02,7782-44-7;CH,O, 2143-68-2; 0, 17778-80-2;CH20, 50-00-0: OH, 3352-57-6; CH302, 2143-58-0;CH2OOH, 74087-87-9.
Partial Specific Vdumes of Methyisucclnates and Poly(itaconate)s I. Hernindez-Fuentes: A. Horta,*t L. gar gal lo,^ C. Abradelo,+M. Yazdani-Pedram,s and D. Radiirs Departamento de Quimica Cisica, Fpcultad de Ciencias Quimicas, Universidad Complutense, 28040 Madrid, Spain; Departamento de Quimica Fisica. Facultad
