Vibrational Linewidth of a Chemisorbed Polyatomic

化学吸附多原子的振动线宽

• 批准号: 8803436
• 负责人: Victoria Buch
• 金额: $ 8.74万
• 依托单位: University of Illinois at Chicago
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-06-01 至 1990-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8803436&HistoricalAwards=false
• 关键词: Vibrational; Linewidth; Chemisorbed; Polyatomic

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.

在物理化学计划的这个项目中，Buch将计算在铂表面化学吸收的分子的振动线形状。计算出的乙基醚分子的线形将与Trenary等人的详细实验结果进行比较。本研究将探讨高频吸附模式对振动展宽机制的影响。计算结果将用于构建“系统/浴池”划分概念的简化模型。由于吸附质振动模式与固体振动模式的相互作用而引起的谱线展宽机制将被研究。将使用原子水平的方法，其中红外线形从微观力场中量子力学地推导出来。重点将放在有序的吸附层上，它将利用系统的周期性来降低问题的维数。系统的零级运动将用绝热近似来描述，在绝热近似中，低频衬底和吸附模态在高频吸附模态的平均场中运动。将计算吸附质的基态和激发态的低频位移，并用于评估脱相对线宽的贡献。振动衰减的贡献将在黄金法则的帮助下计算。计算将不包括可调参数；微观力场数据将采用文献资料。由Trenary等人实验测量的三条光谱线的明显不同的宽度和温度依赖性，将提供一个独特的机会来研究化学吸收多原子的模式特异性效应。这将是第一次对多原子吸附物的红外线形状进行量子力学原子水平的研究，包括对现实微观势的衰变和脱相贡献。