Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew University, Jerusalem 91904, Israel.
Phys Chem Chem Phys. 2011 May 21;13(19):8715-22. doi: 10.1039/c0cp01385d. Epub 2010 Oct 5.
Vibrational energy flow and conformational transitions following excitation of the OH stretching mode of the most stable conformer of glycine are studied by classical trajectories. "On the fly" simulations with the PM3 semiempirical electronic structure method for the potential surface are used. Initial conditions are selected to correspond to the ν=1 excitation of the OH stretch. The main findings are: (1) An an equilibrium-like ratio is established between the populations of the 3 lowest-lying conformers after about 10 picoseconds. (2) There is a high probability throughout the 150 ps of the simulations for finding the molecule in geometries far from the equilibrium structures of the lowest-energy conformers. (3) Energy from the initial excited OH (ν=1) stretch flows preferentially to 5 other vibrational modes, including the bending motion of the H atom. (4) RRK theory yields conformational transition rates that deviate substantially from the classical trajectory results. Possible implication of these results for vibrational energy flow and conformational transitions in small biological molecules are discussed.
通过经典轨迹研究了最稳定构象的甘氨酸 OH 伸缩模式激发后振动能流和构象转变。使用 PM3 半经验电子结构方法对势能面进行了“实时”模拟。初始条件被选择为对应于 OH 伸缩的ν=1 激发。主要发现包括：（1）在大约 10 皮秒后，3 种最低构象的种群之间建立了类似于平衡的比例。（2）在模拟的 150 皮秒内，发现分子在远离最低能量构象平衡结构的几何形状的概率很高。（3）初始激发的 OH（ν=1）伸缩的能量优先流向其他 5 个振动模式，包括 H 原子的弯曲运动。（4）RRK 理论得出的构象转变速率与经典轨迹结果有很大偏差。这些结果对小分子中振动能流和构象转变的可能影响进行了讨论。
