Dynamical Resonances Accessible Only by Reagent Vibrational Excitation in the F + HD→HF + D Reaction
Dynamical Resonances Accessible Only by Reagent Vibrational Excitation in the F + HD→HF + D Reaction
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DOI：
10.1126/science.1246546
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发表时间：
2013-12
期刊：
影响因子：
56.9
通讯作者：
Tao Wang;Jun Chen;Tiangang Yang;C. Xiao;Zhigang Sun;Long Huang;D. Dai;Xueming Yang;Dong H. Zhang
中科院分区：
文献类型：
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作者：
Tao Wang;Jun Chen;Tiangang Yang;C. Xiao;Zhigang Sun;Long Huang;D. Dai;Xueming Yang;Dong H. Zhang
在过去的十年中，分子束研究已经阐明了许多微妙的量子力学因素，这些因素控制着振动激发对基元化学反应结果的影响。然而，这些研究通常不得不集中在可以容易地通过在红外（IR）中的直接吸收而振动的试剂上。Wang等人（第1499页）表明，受激拉曼泵浦的变化可以有效地激发双原子分子氘化氢（HD）中的IR惰性伸缩振动。因此，他们可以探测振动对HD + F反应结果的影响。通过结合光谱和理论研究，他们发现了只能通过振动预激发获得的反应坐标沿着的Feshbach共振。一个有效的振动激发协议，使发现一个不寻常的反应轨迹在一个良好的研究系统。在振动激发效率的实验限制，以前阻碍了调查如何振动能量可能介导的作用，在双分子反应中的动态共振。在这里，我们报告了一个高分辨率的交叉分子束实验的振动激发HD（v = 1）+ F → HF + D反应，其中两个宽峰的后向散射HF（v′ = 2和3）的产品清楚地出现在碰撞能量为0.21千卡/摩尔（千卡/摩尔）和0.62千卡/摩尔的微分截面测量的能量范围内。我们将这些特征归因于势垒后区HF（v′ = 4）-D振动绝热势中的Feshbach共振激发态。在高精度势能面上的量子动力学计算表明，这些共振态与入口通道中的HD（v′ = 1）态相关，因此只能由振动激发的HD试剂进入。
Access via Vibration Molecular beam studies over the past decade have elucidated many subtle quantum mechanical factors governing the influence of vibrational excitation on the outcome of elementary chemical reactions. However, these studies have generally had to focus on reagents that can be easily made to vibrate by direct absorption in the infrared (IR). Wang et al. (p. 1499) show that a variation on stimulated Raman pumping can efficiently excite the IR-inactive stretch vibration in the diatomic molecule, hydrogen deuteride (HD). As a result, they can probe the influence of that vibration on the outcome of the HD + F reaction. Through a combined spectroscopic and theoretical investigation, they uncover Feshbach resonances along the reaction coordinate that are only accessible through vibrational preexcitation. A protocol for efficient vibrational excitation enabled discovery of an unusual reaction trajectory in a well-studied system. Experimental limitations in vibrational excitation efficiency have previously hindered investigation of how vibrational energy might mediate the role of dynamical resonances in bimolecular reactions. Here, we report on a high-resolution crossed-molecular-beam experiment on the vibrationally excited HD(v = 1) + F → HF + D reaction, in which two broad peaks for backward-scattered HF(v′ = 2 and 3) products clearly emerge at collision energies of 0.21 kilocalories per mole (kcal/mol) and 0.62 kcal/mol from differential cross sections measured over a range of energies. We attribute these features to excited Feshbach resonances trapped in the peculiar HF(v′ = 4)–D vibrationally adiabatic potential in the postbarrier region. Quantum dynamics calculations on a highly accurate potential energy surface show that these resonance states correlate to the HD(v′ = 1) state in the entrance channel and therefore can only be accessed by the vibrationally excited HD reagent.