Precision measurements and test of molecular theory in highly excited vibrational states of H ( = 11).

Accurate transition energies in molecular hydrogen were determined for transitions originating from levels with highly excited vibrational quantum number,  = 11, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited , produced via the photodissociation of HS, yielding transition frequencies with accuracies of 45 MHz or 0.0015 cm. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing electronic Rydberg states, resulting in narrow transitions due to reduced ac-Stark effects. Using known level energies, the level energies of ( = 11,  = 1, 3-5) states are derived with accuracies of typically 0.002 cm. These experimental values are in excellent agreement with and are more accurate than the results obtained from the most advanced ab initio molecular theory calculations including relativistic and QED contributions.