FINITE PULSE WIDTHS IN TWO-DIMENSIONAL FOURIER TRANSFORM ESR

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 二维傅立叶变换ESR技术，如2D-Eldor，已显著提高了ESR在复杂流体(如液晶和膜小泡)以及自旋标记聚合物和多肽中的分子动力学研究的分辨率。基于随机刘维尔方程(SLE)的成熟理论被成功地用来分析这些实验。然而，一个基本的假设已经被用来简化复杂的分析，即。这些脉冲被视为理想的非选择性脉冲，因此提供了对整个光谱的均匀照射。在实际实验中，脉冲的宽度是有限的，这会导致与理论预测的偏差，而在更高频率下进行的实验会加剧这个问题。我们发展了一种方法来处理完整的SLE，包括分子动力学、自旋哈密顿量和脉冲过程中的辐射场的显式作用。通过使用Trotter公式，计算变得更易于管理，该公式适合于以我们所称的“分裂超级算子”方法处理这种SLE。给出了不同运动状态下的算例，说明了有限脉冲宽度对二维Eldor谱的影响。该理论与2D-Eldor实验结果符合得很好。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Two-dimensional (2D) Fourier Transform ESR techniques, such as 2D-ELDOR, have considerably improved the resolution of ESR in studies of molecular dynamics in complex fluids such as liquid crystals and membrane vesicles and in spin labeled polymers and peptides. A well-developed theory based on the stochastic Liouville equation (SLE) has been successfully employed to analyze these experiments. However, one fundamental assumption has been utilized to simplify the complex analysis, viz. the pulses have been treated as ideal non-selective ones, which therefore provide uniform irradiation of the whole spectrum. In actual experiments, the pulses are of finite width causing deviations from the theoretical predictions, a problem that is exacerbated by experiments performed at higher frequencies. We have developed a method to deal with the full SLE including the explicit role of the molecular dynamics, the spin Hamiltonian and the radiation field during the pulse. The computations are rendered more manageable by utilizing the Trotter formula, which is adapted to handle this SLE in what we call a "Split Super-Operator" method. Examples are given for different motional regimes, which show how 2D-ELDOR spectra are affected by the finite pulse widths. The theory shows good agreement with 2D-ELDOR experiments performed as a function of pulse width.