Observations of the high vibrational levels of the $B''BÊ^{1}\Sigma_{u}^{+} $state of H$_{2}$

Double-resonance laser spectroscopy via the $EFÊ^{1}\Sigma_{g}^{+} ,Êv'=6,ÊJ'=0-2$state was used to probe the high vibrational levels of the $B''BÊ^{1}\Sigma_{u}^{+} $ state of molecular hydrogen. Resonantly-enhanced multiphoton ionization spectra were recorded by detecting ion production as a function of energy using a time of flight mass spectrometer. New measurements of energies for the v $=$ 51 $-$ 66 levels for the $B''BÊ^{1}\Sigma_{u}^{+} $ state are reported, which, taken with previous results, span the v $=$ 46 $-$ 69 vibrational levels. Results for energy levels are compared to theoretical calculations [L. Wolniewicz, T. Orlikowski, and G. Staszewska, J. Mol. Spec. 238, 118 (2006)]. The average difference between the 84 measured energies and calculated energies is $-$3.8 cm$^{-1}$ with a standard deviation of 5.3 cm$^{-1}$ . This level of agreement showcases the success of the theoretical calculations in accounting for the strong rovibronic mixing of the$^{1}\Sigma_{u}^{+} $and $^{1}\Pi_{u}^{+} $states.