Absolute calibration of theTe2130reference line for positronium1S13−2S13spectroscopy

Abstract

We report on an interferometric frequency measurement of the ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ absorption line which has been used as a reference in Doppler-free two-photon spectroscopy of the positronium $1{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ transition. The measurement relies on a comparison with a nearby, previously calibrated line of ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$. The result, 616803 545.98(71) MHz, lowers the observed value of the positronium $1{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ interval to 1233607 142.9(10.7) and lessens the agreement between theory and experiment.