Fundamental vibration of molecular hydrogen

G. D. Dickenson, M. L. Niu, E. J. Salumbides, J. Komasa, K. S. E. Eikema, K. Pachucki, and W. Ubachs

Accepted Tuesday Apr 23, 2013

The fundamental ground tone vibration of H$_2$, HD, and D$_2$ is determined to an accuracy of $2 \times 10^{-4}$ cm$^{-1}$ from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless vibrational splitting is derived from the combination difference between electronic excitation from the $X^1\Sigma_g^+, v=0$ and $v=1$ levels to a common $EF^1\Sigma_g^+, v=0$ level. Agreement within $1\sigma$ between the experimental result and a full \emph{ab initio} calculation provides a stringent test of quantum electrodynamics in a chemically-bound system.