Domino Tunneling.
Domino Tunneling.
复制标题
DOI：
10.1021/jacs.5b03322
复制
发表时间：
2015
影响因子：
15
通讯作者：
P. Schreiner;J. Wagner;H. Reisenauer;D. Gerbig;D. Ley;János Sarka;A. Császár;Alexander Vaughn;W. D. Allen
中科院分区：
文献类型：
--
作者：
P. Schreiner;J. Wagner;H. Reisenauer;D. Gerbig;D. Ley;János Sarka;A. Császár;Alexander Vaughn;W. D. Allen
近3 K的基质隔离实验和最先进的量子化学计算表明，草酸[1，（COOH）2]表现出以前没有观察到的顺序量子力学隧穿现象。众多的红外（IR）波段的强度被用来监测草酸的最低能量的O-H旋转异构体（1cTc，1cTt，1 tTt）的时间演变长达19天后，近红外照射的矩阵。这些旋转异构体的相对能量分别为0.0（1cTc）、2.6（1cTt）和4.0（1 tTt）kcal mol（-1）。尽管9.7和10.4 kcal mol（-1）的顺序势垒太高而不能在低温条件下热克服，但在不同基质位点观察到1 tTt → 1cTt → 1cTc异构化级联，半衰期（t1/2）为30 - 360 h。建立了一个适用于不同基质位物种级联反应的复杂动力学模型。用这个模型，一个精确的，全球性的非线性最小二乘拟合同时实现了9个红外波段的1cTc，1cTt，和1 tTt旋转异构体的时间配置文件。揭示了快（t（1/2）= 30-50 h）和慢（t（1/2）> 250 h）基质位点的类别，前者的衰变速率与相应孤立分子构象隧穿速率的第一性原理计算密切一致。因此，严格的动力学和理论分析表明，“多米诺骨牌”隧穿机制是在工作中，这些草酸转化。
Matrix-isolation experiments near 3 K and state-of-the-art quantum chemical computations demonstrate that oxalic acid [1, (COOH)2] exhibits a sequential quantum mechanical tunneling phenomenon not previously observed. Intensities of numerous infrared (IR) bands were used to monitor the temporal evolution of the lowest-energy O-H rotamers (1cTc, 1cTt, 1tTt) of oxalic acid for up to 19 days following near-infrared irradiation of the matrix. The relative energies of these rotamers are 0.0 (1cTc), 2.6 (1cTt), and 4.0 (1tTt) kcal mol(-1). A 1tTt → 1cTt → 1cTc isomerization cascade was observed with half-lives (t1/2) in different matrix sites ranging from 30 to 360 h, even though the sequential barriers of 9.7 and 10.4 kcal mol(-1) are much too high to be surmounted thermally under cryogenic conditions. A general mathematical model was developed for the complex kinetics of a reaction cascade with species in distinct matrix sites. With this model, a precise, global nonlinear least-squares fit was achieved simultaneously on the temporal profiles of nine IR bands of the 1cTc, 1cTt, and 1tTt rotamers. Classes of both fast (t(1/2) = 30-50 h) and slow (t(1/2) > 250 h) matrix sites were revealed, with the decay rate of the former in close agreement with first-principles computations for the conformational tunneling rates of the corresponding isolated molecules. Rigorous kinetic and theoretical analyses thus show that a "domino" tunneling mechanism is at work in these oxalic acid transformations.