化学学报 ›› 2013, Vol. 71 ›› Issue (05): 743-748.DOI: 10.6023/A13010049 上一篇    下一篇

研究论文

C4H(X2+)+H2反应机理的直接动力学研究

霍瑞萍a, 张祥b, 黄旭日a, 李吉来a, 孙家锺a   

  1. a 吉林大学理论化学研究所理论化学国家重点实验室 长春 130023;
    b 山西师范大学化学与材料科学学院 临汾 041004
  • 收稿日期:2013-01-10 出版日期:2013-05-14 发布日期:2013-03-05
  • 通讯作者: 李吉来,jilai@jlu.edu.cn E-mail:jilai@jlu.edu.cn
  • 基金资助:

    项目受国家自然科学基金(Nos. 21103064, 21073075, 21173097)、教育部博士点基金(No. 20100061110046)、吉林大学理论化学国家重点实验室专项基金、吉林大学基本科研业务费(Nos. 421010061439, 450060445067)和吉林大学研究生创新基金(20121036)资助.

Mechanism Study of C4H(X2+)+H2 Reaction by Direct Ab Initio Methods

Huo Ruipinga, Zhang Xiangb, Huang Xuria, Li Jilaia, Sun Chiachunga   

  1. a State Key Laboratory of Theoretical & Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, China;
    b School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, China
  • Received:2013-01-10 Online:2013-05-14 Published:2013-03-05
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 21103064, 21073075, 21173097), Research Fund for the Doctoral Program of Higher Education of China (No. 20100061110046), the Special Funding of State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Basic Research Fund of Jilin University (Nos. 421010061439, 450060445067) and the Graduate Innovation Fund of Jilin University (20121036).

贫氢分子CnH是燃烧火焰、行星大气中的重要的中间体. 这些分子与其它一些分子或自由基的反应在星际化学中起着非常重要的作用. 虽然这些分子的电子结构和光谱性质已经进行了广泛的研究, 但是研究这些反应的机理和动力学性质也是亟需的. 因此, 我们采用直接动力学方法对线性分子丁二炔自由基C4H(CCCCH)夺氢气(H2)分子中HAT的反应的微观机理和动力学性质进行了理论研究. 本研究分别在BB1K/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p)和 M06-2x/6-311+G(2d,2p)水平上优化得到了各稳定点的结构及振动频率. 为了得到更为可靠的反应能量和势能面信息, 在BB1K/6-311+G(2d,2p)优化结构的基础上用CCSD(T)/aug-cc-pVTZ水平进行了单点能量校正. 对于此反应研究了两条不同的氢吸附通道, C4H(C1C2C3C4H)中的C1和C4分别吸氢, 即通道1 (R1)和通道2 (R2). 计算得出: 通道1和通道2的能垒分别为3.58 kcal/mol和26.56 kcal/mol, 结果表明C4H中C1端吸氢是主要通道. 反应过程中的电子转移可以为理解氢原子转移(HAT)提供重要的线索, 因此, 我们利用NBO对反应过程中的电子转移行为进行了详细的分析. 本工作运用经典过渡态理论(VTST)与变分过渡态理论(CVT)和变分过渡态理论结合小曲率隧道效应校正(CVT/SCT)的方法计算了该反应在40~1000 K温度区间的速率常数. 除对于最低频率的配分函数采用了阻尼内转动近似外, 其它频率都采用谐振子模型处理. 计算得到的总的CVT/SCT反应速率常数与已有的实验值符合得很好. 我们还提供了40~1000 K温度范围内的三参数Arrhenius表达式. 这些公式有利于今后在较宽的温度范围内迄今没有实验数据的反应的研究.

关键词: C4H, H2, 速率常数, 过渡态理论

Hydrogen-deficient molecules have been implicated as the key intermediates in the combustion, planetary atmospheres, and so on. Their reactions with other molecules and/or radicals play important roles and are hot topic in interstellar chemistry. Although extensive efforts have been addressed on the electronic and spectroscopic properties of these molecules, continued extensive research, for example the kinetics and mechanism of their reactions, is still desirable. Therefore, we investigated the hydrogen abstraction (HAT) reaction by the linear butadiynyl radical C4H (CCCCH) from hydrogen (H2) by direct ab initio kinetics over a wide temperature range 40~1000 K theoretically at the CCSD(T)/aug-cc-pVTZ//BB1K/6-311+G(2d,2p) level of theory. The optimized geometries and frequencies of the stationary points are calculated at the BB1K/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p) and M06-2x/6-311+G(2d,2p) level, respectively. To obtain more reliable reaction energies and barrier heights, high-level single-point calculations for the stationary points have been performed at the CCSD(T)/aug-cc-pVTZ by using BB1K/6-311+G(2d,2p) Cartesian coordinates. Two different hydrogen abstraction channels by C1 and C4 of C4H (C1C2C3C4H) have been explored, namely, Channel 1 (R1) and Channel 2 (R2). The activation barrier heights of Channel 1 and Channel 2 are 3.58 kcal/mol and 26.56 kcal/mol, respectively. The results indicate that C1 position of the C4H is a more reactive site. The electron transfer evolution may offer important clues for understanding hydrogen atom transfer (HAT), we therefore analyzed the electron transfer behaviors by NBO in detail. The theoretical rate constants were predicted by the conventional variational transition state theory (VTST), canonical variational transition-state theory (CVT) incorporating a small-curvature tunneling correction (CVT/SCT) method. For the lowest frequency, the partition function is evaluated using the hindered rotor approximation and the other vibrational modes are treated as quantum mechanical separable harmonic oscillators. The overall CVT/SCT rate constants are excellent in agreement with the available experimental results. The three-parameter expressions of Arrhenius rate constants are also provided within 40~1000 K. It is expected to be helpful for future studies over a wide temperature range where no experimental data available so far.

Key words: C4H, H2, rate constant, transition state theory (TST)