Electric-quadrupole transition of H2determined to10−9precision

Abstract

The $S$(3) electric-quadrupole transition of the (3-0) overtone of molecular hydrogen has been recorded with a continuous-wave cavity ring-down spectrometer and calibrated with sub-megahertz accuracy using a temperature-stabilized Fabry-P\'erot interferometer. The collision-induced frequency shift and the frequency at zero pressure limit are derived from a fit of the spectral profiles. The absolute transition frequency of the $S$(3) line is determined to be 376 531 818.1 MHz with a 1.6-MHz accuracy ($\ensuremath{\delta}\ensuremath{\nu}/\ensuremath{\nu}=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$) by measuring the shift to a Rb line at 795 nm. As the best determined transition frequency of neutral H${}_{2}$ in the ground electronic state, this value agrees well with recent high-level quantum chemistry calculations including relativistic and quantum electrodynamics corrections.