The feasibilty of a hot cathode ion source for the production of molecular noble gas ion has been investigated. The experiments were performed in the primary ion column of a sanning ion microprobe in which the beam is fed through a small aperture after a drift length of approximately one meter. It was found that noble gas ion beams can be produced with a relative dimer-to-monomer content of about 1%. The influence of the source pressure and the discharge voltage on the molecular ion current has been studied in detail. The molecular ion current increases with with decreasing discharge voltage and becomes largest at the minimum accessible (stable) discharge voltage. With increasing source pressure the dimer (and trimer) ion current at the target increases up to a maximum which results from the counteraction of molecular ion production in the source and ion beam attenuation due to interaction with neutrals effusing from the source. The results are discussed with the aim of providing optimization criteria for instrument design and operation.