Measurement of Nuclear Spin Conversion Rates in Molecules

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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.