Cavity ring-down spectroscopy of the electric quadrupole transitions of [formula omitted] in the 784–852 nm region

Abstract

Precision spectroscopy of the hydrogen molecule can be used to verify the quantum electrodynamics theory (QED) in a molecular system. The electric quadrupole transitions of the second overtone of H2 have been recorded with a continuous-wave cavity ring-down spectrometer. In total, eight lines in the 784–852nm range have been observed, including the extremely weak S3(5) line with a calculated intensity of 9.2×10-31cm/molecule. The absolute line positions at the zero pressure limit have been determined with an accuracy of 3×10-4cm-1, agreeing well with the high-level quantum chemical calculations including relativistic and QED corrections. The deviations between the experimental and theoretical frequencies are less than 5×10-4cm-1, which is only 20% of the claimed theoretical uncertainty.