Precision measurements are performed on highly excited vibrational quantum
states of molecular hydrogen. The v=12,J=0β3 rovibrational levels of H2β
(X1Ξ£g+β), lying only 2000 cmβ1 below the first dissociation
limit, were populated by photodissociation of H2βS and their level energies
were accurately determined by two-photon Doppler-free spectroscopy. A
comparison between the experimental results on v=12 level energies with the
best \textit{ab initio} calculations shows good agreement, where the present
experimental accuracy of 3.5Γ10β3 cmβ1 is more precise than
theory, hence providing a gateway to further test theoretical advances in this
benchmark quantum system.Comment: 5 pages, 4 figures, and 2 table