Measurement of Nuclear Spin Conversion Rates in Molecules

该项目的目的是通过应用光致漂移方法测量甲醇及其同位素物种的核自旋转换率。从理论上讲，目的是计算甲醇及其同位素的A和E物种的扭转-旋转能级，并分析转化率以确定A和E物种之间的能量差。我们的目的也包括观察在外加电场中能级交叉所引起的转化率的变化。根据研究计划的描述，研究结果如下。我们开发了一个实验装置的光致漂移和转换率的测量。然而，我们发现探测激光器的频率和输出功率的稳定性不足以以所需的精度测量转换率。我们已经开发了这种稳定的探测激光器。在一个改进的装置中，我们观察到了^CH_3F的邻-对位转化率<13>及其随外加电场的增加。然而，在对甲醇分子进行研究之前，我们还需要进一步提高实验精度，在精确能级和扭转势垒的确定方面，我们得到了以下结果。在参考文献（3）和（5）中，我们用实验方法测定了高精度的扭转-转动能级。在理论上，文献[1]发展了含新高阶项的扭-转哈密顿量，并用于确定CH_3^ OH的能级<18>，文献[2]发展了计算甲醇离心畸变常数的理论。文献（4）和（6）分别计算了CH_3OH和CD_3OH的离心畸变常数（包括同位素）。

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.