用从头计算法研究甲烷质子反应的微观机理

AN AB INITIO STUDY ON THE MICROSCOPIC MECHANISM OF THE REACTION OF METHANE AND PROTON

用STO-3G基集及能量梯度构型自动优化法,研究了H^++CH_4—→ECH^+_2]—→H_2+CH^+_3反应的最小能量途径。通过对H^+的四种进攻方向及H_2的两种离去方向的计算知道,这是一个前向型的S_(E2)反应。H^+有两种进攻方向,分别构成一种一步的反应机理和两种二步的反应机理。在两种二步的反应机理中,CH^+_2分别是中间体和准中间体。H^+进攻中是否存在化学反应集中完成的突变区对微观反应途径的竞争起着首要的作用。

The minimum energy patb of the reaction H^++CH_4→[CH_3]^+→H_2+CH_3^+ has been studied by using STO-3G with energy gradient automatic geometry optimization. Resulting from calculation about four kinds of H^+ attack direction and two kinds of H_2 leave direction, the conclusion is that this is a S_(E2) reaction of forward form. Two attack directions of H^+ are effective, forming two kinds of reaction mechanisms, one with one uni-step and the other with two bi-steps. The CH_5^+ in the latter is the intermediate and the quasi-intermediate respectively. It seems of prime importance for the competition of the reaction microscopic paths whether the discontinued zone, in which chemical reaction completes as H^+ attacks, is existent.