Temperature and Pressure-Dependent Rate Coefficients for the Reaction of Vinyl Radical with Molecular Oxygen

State-of-the-art
calculations of the C2H3O2 potential
energy surface are presented. A new method
is described for computing the interaction potential for R + O2 reactions. The method, which combines accurate determination
of the quartet potential along the doublet minimum energy path with
multireference calculations of the doublet/quartet splitting, decreases
the uncertainty in the doublet potential and thence the rate constants
by more than a factor of 2. The temperature- and pressure-dependent
rate coefficients are computed using variable reaction coordinate
transition-state theory, variational transition-state theory, and
conventional transition-state theory, as implemented in a new RRKM/ME
code. The main bimolecular product channels are CH2O +
HCO at lower temperatures and CH2CHO + O at higher temperatures.
Above 10 atm, the collisional stabilization of CH2CHOO
directly competes with these two product channels. CH2CHOO
decomposes primarily to CH2O + HCO. The next two most significant
bimolecular products are OCHCHO + H and 3CHCHO + OH, and
not C2H2 + HO2. C2H3 + O2 will be predominantly chain branching above
1700 K. Uncertainty analysis is presented for the two most important
transition states. The uncertainties in these two barrier heights
result in a significant uncertainty in the temperature at which CH2CHO + O overtakes all other product channels.

本研究报道了C₂H₃O₂势能面（potential energy surface）的当前最高精度计算结果。本文提出了一种用于计算R + O₂类反应相互作用势能的新方法：该方法结合沿二重态（doublet）最低能量路径的四重态（quartet）势能精准测定，与二重态/四重态劈裂的多参考态计算（multireference calculations），将二重态势能乃至速率常数的不确定度降低了超过2倍。借助全新开发的RRKM/ME程序中实现的可变反应坐标过渡态理论（variable reaction coordinate transition-state theory）、变分过渡态理论（variational transition-state theory）与传统过渡态理论（conventional transition-state theory），本研究计算得到了温度与压力依赖的速率系数。低温下主要双分子产物通道为CH₂O + HCO，高温下则为CH₂CHO + O。当压力超过10 atm时，CH₂CHOO的碰撞稳定化过程会与上述两类产物通道形成直接竞争。CH₂CHOO主要分解为CH₂O + HCO。其次两类最重要的双分子产物为OCHCHO + H与³CHCHO + OH，而非C₂H₂ + HO₂。当温度高于1700 K时，C₂H₃ + O₂反应将主要发生链支化过程。本文对两类最重要的过渡态（transition state）进行了不确定度分析：这两个势垒高度的不确定度，会导致CH₂CHO + O取代所有其他产物通道成为主导反应的临界温度存在显著不确定度。