Seifert G, Patzlaff T, Graener H
Fachbereich Physik, Martin-Luther-Universität, Halle-Wittenberg, D-06099 Halle, Germany.
J Chem Phys. 2006 Oct 21;125(15):154506. doi: 10.1063/1.2355489.
The vibrational dynamics of isolated water molecules dissolved in the nonpolar organic liquids 1,2-dichloroethane (C(2)H(4)Cl(2)) and d-chloroform (CDCl(3)) have been studied using an IR pump-probe experiment with approximately 2 ps time resolution. Analyzing transient, time, and spectrally resolved data in both the OH bending and the OH stretching region, the anharmonic constants of the bending overtone (v=2) and the bend-stretch combination modes were obtained. Based on this knowledge, the relaxation pathways of single water molecules were disentangled comprehensively, proving that the vibrational energy of H(2)O molecules is relaxing following the scheme OH stretch-->OH bend overtone-->OH bend-->ground state. A lifetime of 4.8+/-0.4 ps is determined for the OH bending mode of H(2)O in 1,2-dichloroethane. For H(2)O in CDCl(3) a numerical analysis based on rate equations suggests a bending overtone lifetime of tau(020)=13+/-5 ps. The work also shows that full 2-dimensional (pump-probe) spectral resolution with access to all vibrational modes of a molecule is required for the comprehensive analysis of vibrational energy relaxation in liquids.
利用时间分辨率约为2皮秒的红外泵浦-探测实验，研究了溶解在非极性有机液体1,2-二氯乙烷（C₂H₄Cl₂）和氘代氯仿（CDCl₃）中的孤立水分子的振动动力学。通过分析OH弯曲和OH伸缩区域的瞬态、时间和光谱分辨数据，得到了弯曲泛音（v = 2）和弯曲-伸缩组合模式的非谐常数。基于这些知识，全面解析了单个水分子的弛豫路径，证明H₂O分子的振动能量按照OH伸缩→OH弯曲泛音→OH弯曲→基态的模式弛豫。确定了H₂O在1,2-二氯乙烷中的OH弯曲模式的寿命为4.8±0.4皮秒。对于CDCl₃中的H₂O，基于速率方程的数值分析表明弯曲泛音寿命为τ(020)=13±5皮秒。这项工作还表明，对液体中振动能量弛豫进行全面分析需要具备分子所有振动模式的全二维（泵浦-探测）光谱分辨率。
