DISSOCIATION-ENERGIES OF THE HYDROGEN AND DEUTERIUM MOLECULES

Fluorescence-excitation spectroscopy near approximately 84 nm has been used to measure the threshold for the dissociation of H-2(B' 1SIGMA(u )+)=H(1s)+H(2s) at 118 377.06 +/- 0.04 cm-1 and the corresponding limi t for D2 at 119 029.72 +/- 0.04 cm-1. The onset of dissociation was ob served clearly, free from overlapping molecular lines, by the use of d elayed quenching of 2s atoms produced by the photoexcitation pulse. Th ese measurements have yielded the values D0(H-2) = 36118.11 +/- 0.08 c m-1 and D0(D2) = 36748.38 +/- 0.07 cm-1 for the dissociation energies of the ground electronic states X 1SIGMA(g)+, in agreement with the la test ab initio calculations, which include nonadiabatic, relativistic, and radiative corrections. From the present values and recently deter mined ionization energies of H-2 and D2, the dissociation energies of the respective ions were found to be D0(H-2+) = 21379.37 +/- 0.08 cm-1 and D0(D2+) = 21711.64 +/- 0.07 cm-1, also in agreement with recent a b initio calculations.