Measurement of Nuclear Spin Conversion Rates in Molecules

本项目的目的是应用光诱导漂移法测量甲醇及其同位素的核自旋转化率。理论上，目的是计算甲醇及其同位素的A、E两种组分的扭旋能级，分析其转化率，确定A、E两种组分之间的能差。我们的目的还包括观察在外加电场中通过平交道口的转换率的变化。根据Research Plan的描述，研究结果如下：我们开发了一个实验装置，用于光诱导漂移和转换率的测量。然而，我们发现探针激光器在频率和输出功率方面的稳定性不足以以所需的精度测量转换率。我们开发了这种稳定的探测激光器。在改进的装置中，我们观察到^<13>CH_3F的正交对位转化率及其在外加电场中的增加。然而，在研究甲醇分子之前，我们还需要进一步提高实验精度。对于精确能级和扭转势垒的确定，我们得到了以下结果。在文献(3)和(5)中，我们通过实验高精度地确定了扭转-旋转能级。理论上，提出了具有新的高阶项的扭转-旋转哈密顿量，并应用于文献(1)中CH_3^<18>OH的能级测定。文献(2)提出了计算甲醇离心畸变常数的理论。参考文献(4)和(6)分别计算了含同位素的CH_3OH和CD_3OH的离心畸变常数。

The purpose of the project is the measurement of the nuclear spin conversion rates of methanol and its isotopic species by applying the light induced drift method. Theoretically, the purpose is the calculation of torsion-rotation energy levels of the A and E species of methanol and its isotopic species and the analysis of the conversion rates to determine the energy difference between the A and E species. Our purpose also includes the observation of the change of the conversion rates by the level crossing in applied electric field.In accordance with the description for Research Plan, the research results are as follows. We developed an experimental setup for the light induced drift and measurement of conversion rates. However, we found that the stability of the probe laser was not enough in the frequency and output power to measure the conversion rates with a required precision. We have developed this stable probe laser. In an improved setup we have observed the ortho-para conversion rate for ^<13>CH_3F and its increase in applied electric fields. However, we have to improve experimental accuracy further before we study the methanol molecule.As for the determination of precise energy levels and the torsional potential barrier, we have obtained the following results. In references (3) and (5), we experimentally determined torsion-rotation energy levels with a high precision. Theoretically, torsion-rotation Hamiltonian with new higher order terms was developed and applied to determine energy levels for CH_3^<18>OH in reference (1).Theory to calculate centrifugal distortion constants was developed for methanol in reference (2). Centrifugal distortion constants for CH_3OH and CD_3OH including isotopic species have been calculated in references (4) and (6), respectively.