Evaluation of a Stark Voltmeter

An absorption Stark voltmeter, using a Fabry-Perot absorption cell with a rotational transition of CH3CN at 36 GHz, has been built and evaluated. The rotational constant and dipole moment of this molecule have been redetermined and found to have the values 9198.56±0.10 GHz and 3.9185±0.0020 Debye, respectively. The short term precision of the device when used as a standard cell was better than that of the equipment which was used to test it, and was probably better than one part in 105, but there were unexplained drifts of 2 parts in 104 per day. The accuracy of the device, as a means of measuring voltage in terms of atomic and molecular constants, is 5 parts in 104. The principal errors are due to the measurement of the plate spacing (which could be reduced by using an optical interferometer to measure spacing), pulling the interferometer resonance by the external circuit, and the effects of field non-uniformities due to the coupling holes.