The Choice of a Molecule for a Beam Frequency Standard

The factors affecting the choice of a molecule for use as an electrical resonance beam frequency standard are discussed in terms of five sources of error. These sources of error are shown to place serious constraints on the physical properties of desirable molecules. The properties of a number of molecules including LiF, BaO, H2S, SO2 and CO are examined and it is shown that it should be possible to build a molecular beam frequency standard with an accuracy of about a part in 10¹³.