Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
J Chem Phys. 2009 Dec 28;131(24):244302. doi: 10.1063/1.3276633.
We report quasiclassical trajectory (QCT) calculations of the correlated product distributions and branching ratios of the reactions F+CHD(3)(v(1)=0,1)-->HF(v)+CD(3)(v) and DF(v)+CHD(2)(v) using a recently published ab initio-based full-dimensional global potential energy surface [G. Czako et al., J. Chem. Phys. 130, 084301 (2009)]. Harmonic normal mode analysis is done for the methyl products to determine the classical actions of each normal mode and then standard histogram binning and Gaussian binning (GB) methods are employed to obtain quantum state-resolved probabilities of the products. QCT calculations have been performed for both the vibrationally ground state and the CH stretching excited F+CHD(3)(v(1)=0,1) reactions at eight different collision energies in the 0.5-7.0 kcal/mol range. HF and DF vibrationally state-resolved rotational and angular distributions, CD(3) and CHD(2) mode-specific vibrational distributions, and correlated vibrationally state-specific distributions for the product pairs have been obtained and the correlated results were compared to the experiment. We find that the use of GB can be advantageous especially in the threshold regions. The CH stretching excitation in the reactant does not change the CD(3) vibrational distributions significantly, whereas the HF molecules become vibrationally and rotationally hotter. On the other hand in the case of the DF+CHD(2) channel the initially excited CH stretch appears mainly "intact" in the CHD(2) product and the DF distributions are virtually the same as formed from the ground state CHD(3) reaction. The computed results qualitatively agree with recent crossed molecular beam experiment [W. Zhang et al., Science 325, 303 (2009)] that (a) CHD(2)(v(1)=1) is the most populated product state of the F+CHD(3)(v(1)=1) reaction and this reaction produces much less CHD(2)(v=0) compared to the reaction F+CHD(3)(v=0); (b) the cross section ratio of CHD(2)(v(1)=1):CHD(2)(v=0) formed from the reactions F+CHD(3)(v(1)=1):F+CHD(3)(v=0) is less than 1 and shows little collision energy dependency; (c) the reactant CH stretch excitation increases the DF:HF ratio at low collision energies; (d) the correlated vibrational and angular distributions for DF(v)+CHD(2)(v(1)=0,1) from the ground state and stretch-excited reactions, respectively, are almost identical.
我们报道了使用最近发表的基于从头算的全维全局势能面[G. Czako 等人，J. Chem. Phys. 130, 084301 (2009)]对反应 F+CHD(3)(v(1)=0,1)-->HF(v)+CD(3)(v)和 DF(v)+CHD(2)(v)的相关产物分布和分支比进行准经典轨迹(QCT)计算。对甲基产物进行谐波正则模态分析，以确定每个正则模态的经典作用，然后采用标准直方图-bin 和高斯-bin (GB)方法获得产物的量子态分辨概率。在 0.5-7. 0 kcal/mol 范围内的八个不同碰撞能下，对振动基态和 CH 拉伸激发的 F+CHD(3)(v(1)=0,1)反应进行了 QCT 计算。得到了 HF 和 DF 振动态分辨的转动和角分布、CD(3)和 CHD(2)模式特定的振动分布，以及产物对的相关振动态特异性分布，并将相关结果与实验进行了比较。我们发现，GB 的使用特别在阈值区域是有利的。反应物中的 CH 拉伸激发并没有显著改变 CD(3)的振动分布，而 HF 分子变得更加振动和转动。另一方面，在 DF+CHD(2)通道的情况下，初始激发的 CH 拉伸主要以“完整”的 CHD(2)产物出现，而 DF 分布几乎与来自基态 CHD(3)反应的相同。计算结果定性上与最近的交叉分子束实验[W. Zhang 等人，Science 325, 303 (2009)]一致，即(a)在 F+CHD(3)(v(1)=1)反应中，CHD(2)(v(1)=1)是最主要的产物态，与反应 F+CHD(3)(v=0)相比，该反应产生的 CHD(2)(v=0)要少得多；(b)从反应 F+CHD(3)(v(1)=1):F+CHD(3)(v=0)形成的 CHD(2)(v(1)=1):CHD(2)(v=0)的截面比小于 1，并且对碰撞能的依赖性很小；(c)反应物 CH 拉伸激发在低碰撞能下增加了 DF:HF 比；(d)来自基态和拉伸激发反应的 DF(v)+CHD(2)(v(1)=0,1)的相关振动和角分布几乎相同。
