Double resonance spectroscopy of the D1Πu+ and B"(B)over-bar1Σu+ states near the third dissociation threshold of H2

Double-resonance laser spectroscopy via the E, F-1 Sigma(+)(g), v' = 6, J' state was used to probe the energy region below the third dissociation limit of molecular hydrogen. Resonantly enhanced multi-photon ionization spectra were recorded by detecting ion production as a function of energy using a time-of-flight mass spectrometer. Energies and line widths for the v = 14-17 levels of the D-1 Pi(+)(u) state of H-2 are reported and compared to experimental data obtained by using VUV synchrotron light excitation (Dickenson et al 2010 J. Chem. Phys. 133 144317) and fully ab initio non-adiabatic calculations of D-1 Pi(+)(u) state energies and line widths (Glass-Maujean et al 2012 Phys. Rev. A 86 052507). Several high vibrational levels of the B ''(B) over bar (1)Sigma(+)(u) state were also observed in this region. Term energies and rotational constants for the v = 67-69 vibrational levels are reported and compared to highly accurate ro-vibrational energy level predictions from fully ab initio non-adiabatic calculations of the first six (1)Sigma(+)(u) levels of H-2 (Wolniewicz et al 2006 J. Mol. Spectrosc. 238 118). While additional observed transitions can be assigned to other states, several unassigned features in the spectra highlight the need for a fully integrated theoretical treatment of dissociation and ionization to understand the complex pattern of highly vibrationally excited states expected in this region.