Determination of the dipole moment of O-18 methanol by microwave Stark spectroscopy

Abstract

In this paper we report accurate measurements of microwave (MW) frequencies for nine different transitions in the first four torsional states in the ground vibrational state of O-18 substituted methanol, for a wide range of applied dc electric field. The Stark-shifted frequencies were measured with accuracies of about ±10 kHz. The results were analyzed to deduce accurate dipole moment values for the four torsional states involved. Substantial variation of dipole moment was observed as a function of the torsional state. The zero field frequencies have been also determined with much better precision than known before. The dipole moment values for the torsional ground state have been determined to be μ_a= 0.8992(8) and μ_b= 1.4226(3) D. The dipole moment value increases with torsional excitation. These values will be useful for the evaluation of relative intensities of interstellar microwave and millimeter wave transitions and optically pumped far infrared laser lines.