Vibrational Linewidth of a Chemisorbed Polyatomic

在物理化学计划的这个项目中，布赫将计算被化学吸附在铂表面的分子的振动线形状。然后将计算的乙叉分子的线形与Trenary等人的详细实验结果进行比较。本研究将考察高频吸附模式对振动展宽机制的影响。然后，计算结果将被用来构建“系统/浴池”分区概念的简化模型。我们将研究由于吸附物的振动模式与固体的振动模式相互作用而产生的谱线展宽机制。将使用一种原子水平的方法，其中红外线形是从微观力场的量子力学中得出的。重点将放在有序的吸附覆盖层上，这将利用系统的周期性来降低问题的维度。系统的零级运动可用绝热近似来描述，在绝热近似下，低频基模和吸附模沿高频吸附模场移动。由此产生的低频位移将被计算为吸附物的基态和激发态，并用于评估消相对线宽的贡献。振动衰变贡献将在黄金法则的帮助下计算。计算将不包括可调参数；有关微观力场的数据将采用文献中的数据。Trenary等人实验测量的三条谱线具有明显不同的宽度和温度依赖性，这将为研究化学吸附多原子中的模式特定效应提供一个独特的机会。这将是第一次对多原子吸附物的红外谱线形状进行量子力学原子水平的研究，包括对真实微观势的衰减和退相贡献。

In this project in the Physical Chemistry Program, Buch will calculate the vibrational line shapes of molecules which are chemically absorbed on the surface of platinum. The calculated line shapes for the ethylidyde molecule will then be compared with the detailed experimental results of Trenary et al. This study will examine the influence of the high frequency adsorbate modes on the vibrational broadening mechanisms. The results of the calculations will then be used to construct simplified models of a "system/bath" partition concept. Line broadening mechanisms due to the interaction of the vibrational modes of the adsorbate with those of the solid will be studied. An atomic level approach will be used in which IR line shapes are derived quantum-mechanically from the microscopic force field. The focus will be on ordered overlayers of adsorbate which will take advantage of system periodicity to reduce the dimensionality of the problem. Zero order motion of the system will be described by the adiabatic approximation, in which the low frequency substrate and adsorbate modes move in the average field of the high frequency adsorbate modes. The resulting shifts in the low frequencies will be calculated for both the ground and excited states of the adsorbate, and used to evaluate the dephasing contribution to the linewidth. The vibrational decay contribution will be calculated with the help of the golden rule. The calculations will include no adjustable parameters; the data on the microscopic force field will be adopted from the literature. The markedly different widths and temperature dependencies of the three spectral lines measured experimentally by Trenary et al., will offer a unique opportunity to study mode specific effects in a chemisorbed polyatomic. This will be the first quantum-mechanical atomic level study of IR line shapes of a polyatomic adsorbate, including both decay and dephasing contributions for a realistic microscopic potential.