Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Campus Nord B4-B5, Barcelona 08034, Spain.
Phys Chem Chem Phys. 2012 May 14;14(18):6332-42. doi: 10.1039/c2cp23555b. Epub 2012 Mar 8.
We extend, via a reformulation in terms of Poisson brackets, the method developed previously (Rey et al., J. Phys. Chem. A, 2009, 113, 8949) allowing analysis of the pathways of an excited molecule's ultrafast vibrational relaxation in terms of intramolecular and intermolecular contributions. In particular we show how to ascertain, through the computation of power and work, which portion of an initial excess molecular energy (e.g. vibrational) is transferred to various degrees of freedom (e.g. rotational, translational) of the excited molecule itself and its neighbors. The particular case of bend excess energy relaxation in pure water is treated in detail, completing the picture reported in the work cited above. It is shown explicitly, within a classical description, that almost all of the initial water bend excitation energy is transferred-either indirectly, via Fermi resonance centrifugal coupling to the bend-excited water's rotation, or directly via intermolecular coupling- to local water librations, only involving molecules in the first two hydration shells of the vibrationally excited water molecule. Finally, it is pointed out that the Poisson bracket formulation can also be applied to elucidate the microscopic character of solvation and rotational dynamics, and should prove useful in developing a quantum treatment for energy flow in condensed phases.
我们通过泊松括号的重新表述，扩展了之前（Rey 等人，J. Phys. Chem. A，2009，113，8949）发展的方法，该方法允许根据分子内和分子间贡献来分析激发分子超快振动弛豫的途径。特别是，我们展示了如何通过计算功率和功来确定初始过量分子能量（例如振动）的哪一部分转移到激发分子本身及其邻居的各种自由度（例如旋转、平移）。详细处理了纯水中弯曲过剩能量弛豫的特殊情况，完成了上述引用工作中报道的情况。在经典描述中明确表明，初始水弯曲激发能量几乎全部被转移——要么通过费米共振离心耦合间接转移到弯曲激发水的旋转，要么直接通过分子间耦合转移到局部水的旋转运动，仅涉及振动激发水分子的前两个水合壳层中的分子。最后，指出泊松括号公式也可用于阐明溶剂化和旋转动力学的微观特征，并且应该有助于开发凝聚相能量流的量子处理。
