Frequency reference in the 732-nm region for precision laser spectroscopy of muonium

A search is performed for a frequency reference in the 732-nm region, which is required to calibrate a laser spectrometer in experiments on precision measurements of the 1S — 2S transition frequency in muonium. The adequate reference is found in the absorption spectrum of molecular iodine vapours heated to 600°C. The reference frequency is less than 1 GHz away from the required spectrometer frequency tuned to the resonance in muonium.