Theoretical study and rate constant calculation of the CH[sub 2]O+CH[sub 3] reaction.

The potential energy surface of the CH[sub 2]O+CH[sub 3] reaction is explored at the MP2/6-311++G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single point) levels of theory. Theoretical calculations suggest that the major product channel (R1) is the hydrogen abstraction leading to the product P[sub 1] CHO+CH[sub 4] (R1), while the addition process leading to P[sub 2]H+CH[sub 3]CHO (R2) appears to be negligibly small. The calculated enthalpies and dissociation activation energies for CH[sub 3]CH[sub 2]O and CH[sub 3]OCH[sub 2] radicals involved in the reaction are in line with the experimental values. Dual-level dynamics calculation is carried out for the direct hydrogen abstraction channel. The energy profile of (R1) is refined with the interpolated single-point energies (ISPE) method at the QCISD(T)//MP2 level. The rate constants, which are evaluated by canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction, are in good agreement with the available experimental data. It is shown that tunneling effect plays a significant role in the rate constant calculation; and as a result, the CVT/SCT rate constants exhibit typical non-Arrhenius behavior over a wide temperature range 300–2000 K. The three parameter expression is k=6.35×10[sup -26] T[sup 4.4] exp(-2450/T) cm[sup 3] molecule[sup -1] s[sup -1]. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]