Laser Studies of Energy Flow in Polyatomic Molecules

实验物理化学计划支持哥伦比亚大学的乔治·W·弗林教授继续研究具有“化学意义”振动能量的分子的碰撞动力学和驰豫。弗林教授将使用准分子泵浦的染料激光或光学参量振荡器来制备高能或反应性施主分子，然后使用IR/VIS吸收或UV荧光来监测碰撞或反应产物的最终量子态。多普勒分辨红外二极管激光光谱仪将提供有关产物分子速度的信息。因此，弗林教授可以确定能量受体(BASH)分子的振动、转动和平移能量。最终目标是确定能量传递分布函数P(E，E‘)，即，分子最初处于能量E时，随着E’-E振动能的变化，发生碰撞诱导跃迁到能量E‘的概率。PI将研究猝灭振动“暗”态的激发机制，并将测量低温(10K)下的分布函数，以测量松弛过程中碰撞速度和络合物形成的影响。这项研究的重要性在于，它揭示了分子解离、分离和重组的机制。通常，我们假设振动能量的损失是由分子之间非常强的碰撞控制的，但与其他过程的细节相比，这是一个粗略的近似，例如，离解率作为能量的函数。弗林教授将获得的分布函数，与良好的理论计算相结合，应该可以更深入地理解对燃烧和大气化学如此重要的解离和复合过程。

The Experimental Physical Chemistry Program supports Prof. George W. Flynn of Columbia University in his continuing studies on collision dynamics and relaxation of molecules with `chemically significant` amounts of vibrational energy. Prof. Flynn will prepare high energy or reactive donor molecules using excimer-pumped dye lasers or optical parametric oscillators and then monitor the final quantum state of the collision or reaction products using IR/VIS absorption or UV fluorescence. Doppler-resolved IR diode laser spectroscopy will yield information on the velocity of product molecules. Thus Prof. Flynn can determine the vibrational, rotational and translational energy of the energy acceptor (bath) molecules. The ultimate goal is to determine the energy transfer distribution function P(E,E'), i.e., the probability that a molecule, initially at an energy E, will undergo a collision induced transition to an energy E', with change in vibrational energy of E'-E. The PI will investigate the mechanism for excitation of quencher vibrational 'dark' states and will measure the distribution function at low temperatures (10K) to gauge the effects of collision velocity and complex formation in the relaxation process. The importance of the research is that it sheds light on the mechanism by which molecules dissociate, or break apart, and recombine. Normally, we assume that the loss of gain of vibrational energy is controlled by very strong collisions between molecules, but this is a gross approximation compared to the detail with which other processes, for example, the dissociation rate as a function of energy, are known. The distribution function that Prof. Flynn will obtain, when coupled with good theoretical calculations, should allow a much deeper understanding of the dissociation and recombination processes that are so important to combustion and atmospheric chemistry.