Stark Voltmeter as an Electromotive Force Reference

An experimental study on a voltmeter application of the Stark effect in molecular rotational transitions aiming at an atomic voltage standard is described. A spectrometer using a Fabry-Perot resonator type Stark cell is built and the transitions J =2←1, Δ M =±1 of s-trioxane C 3 H 6 O 3 in the ground vibrational state at 21 GHz were observed. Preliminary values of the rotational constant B and µ/ h (µ: dipole moment) are found to be 5273.2503±0.0006 MHz and (3.11536±0.00024)×10 8 esu, respectively. The estimated reproducibility of the voltmeter is 80 ppm at about 350 V/cm. Effects of three factors, Q-pulling of the cell, rf leakage field coupling in an external circuit and a frequency pulling by satellite lines, on the accuracy of the frequency measurement of spectra are discussed. The Stark cell is particularly devised for this study so as to establish an extremely uniform dc electric field and desired electrode separation. Performance of each part of the voltmeter is also reviewed.