Gerade/ungerade symmetry- breaking in HD at the n =2 dissociation limit
We report on a study of the I'1Πg outer well state of HD. Via a resonance-enhanced XUV + IR (extreme ultraviolet + infrared) excitation scheme, rovibronic levels (v = 0-2, J = 1-4) are populated and probed by pulsed lasers. Level energies are measured with an accuracy of 0.03 cm-1. Due to gerade-ungerade symmetry breaking, the long-range behavior of the I' potential in HD deviates from that of H2 and D2. When this deviation is taken into account a semi-empirical potential for the I'1Πg state may be constructed, resulting in better agreement with the observed level energies than derived from an adiabatic ab initio potential. With this new potential it is predicted that the I' well can sustain only 4 vibrational levels, with the v = 3 level having a binding energy of 1.38(3) cm-1. PACS Nos.: 33.80.Rv, 34.20.Cf, 33.20.Ni, 31.50.+w
Dissociation energies of the hydrogen and deuterium molecules.
Fluorescence-excitation spectroscopy near [similar to]84 nm has been used to measure the threshold for the dissociation of H[sub 2]([ital B][prime] [sup 1][Sigma][sub [ital u]][sup +])=H(1[ital s])+H(2[ital s]) at 118 377.06[plus minus]0.04 cm[sup [minus]1] and the corresponding limit for D[sub 2] at 119 029.72[plus minus]0.04 cm[sup [minus]1]. The onset of dissociation was observed clearly, free from overlapping molecular lines, by the use of delayed quenching of 2[ital s] atoms produced by the photoexcitation pulse. These measurements have yielded the values [ital D][sub 0](H[sub 2])=36 118.11[plus minus]0.08 cm[sup [minus]1] and [ital D][sub 0](D[sub 2])=36 748.38[plus minus]0.07 cm[sup [minus]1] for the dissociation energies of the ground electronic states [ital X] [sup 1][Sigma][sub g][sup +], in agreement with the latest [ital ab] [ital initio] calculations, which include nonadiabatic, relativistic, and radiative corrections. From the present values and recently determined ionization energies of H[sub 2] and D[sub 2], the dissociation energies of the respective ions were found to be [ital D][sub 0](H[sub 2][sup +])=21 379.37[plus minus]0.08 cm[sup [minus]1] and [ital D][sub 0](D[sub 2][sup +])=21 711.64[plus minus]0.07 cm[sup [minus]1], also in agreement with recent [ital ab] [ital initio] calculations.
Double Configuration Self‐Consistent Field Study of the 1Πu, 3Πu, 1Πg and 3Πg States of H2
Complete potential energy curves for the four lowest‐lying Π states of the hydrogen molecule are calculated using an hierarchy of one‐ and two‐configuration model wavefunctions: the Hartree–Fock model, the configuration interaction model, and the optimal double configuration model (a double configuration SCF model). Comparison and evaluation of the three models are given as a function of internuclear separation of the nuclei for the 1Πu state. An extended basis set of 10 Slater‐type orbitals on each nucleus is scaled optimally for the 1Πu state; the spectroscopic constants for this state are in excellent agreement with experiment. The basis set used for the 1Πu state is employed in determining the potential energy curves for the 3Πu, 1Πg, and 3Πg states; the 3Πu state shows good agreement with experiment, and the essential features for the Πg states are characterized properly.