Chipman Daniel M
Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA.
J Chem Phys. 2006 Jan 28;124(4):044305. doi: 10.1063/1.2162542.
The lowest singlet excited electronic state of water monomer in the gas phase is strictly dissociative along a OH stretch coordinate but changes its nature when the stretched OH moiety is hydrogen bonded to a neighboring water molecule. This work extends previous exploration of the water dimer excited singlet potential-energy surface, using computational methods that are reliable even at geometries well removed from the ground-state equilibrium. First, the hydrogen-bonded OH moiety is stretched far enough to establish the existence of a barrier that is sufficient to support a quasibound vibrational state of the OH oscillator near the Franck-Condon region. Second, the constraint of an icelike structure is relaxed, and it is found that a substantial fraction of liquidlike structures also supports a quasibound vibrational state. These potential-energy explorations on stretching of the hydrogen-bonded OH moiety in a water dimer are discussed as a model for understanding the initial dynamics upon excitation into the lowest excited singlet state of condensed water. The possibility is raised that the excited-state lifetime may be long enough to allow for exciton migration, which would provide a mechanism for energy transport in condensed water phases.
气相中水分子单体的最低单重激发电子态沿OH伸缩坐标是严格解离的，但当被拉伸的OH部分与相邻水分子形成氢键时，其性质会发生变化。这项工作扩展了之前对水二聚体激发单重态势能面的探索，使用了即使在远离基态平衡的几何构型下也可靠的计算方法。首先，将形成氢键的OH部分拉伸到足够远的距离，以确定存在一个足以支持弗兰克-康登区域附近OH振子准束缚振动态的势垒。其次，放松类冰结构的约束，发现相当一部分类液体结构也支持准束缚振动态。这些关于水二聚体中氢键OH部分拉伸的势能探索被作为一个模型来讨论，以理解凝聚态水激发到最低激发单重态时的初始动力学。有人提出，激发态寿命可能足够长，以允许激子迁移，这将为凝聚态水相中能量传输提供一种机制。
