Ab initio calculations with a nonspherical Gaussian basis set: Excited states of the hydrogen molecule

Abstract

Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations Simultaneous optimization of exponents, centers of Gaussian-type basis functions, and geometry with fullconfiguration interaction wave function: Application to the ground and excited states of hydrogen molecule Helium dimer potential from symmetry-adapted perturbation theory calculations using large Gaussian geminal and orbital basis sets

Spectroscopic Observation and Characterization of H+H− Heavy Rydberg States

“…It is noted that perturbations with covalent states exist at internuclear separations of 36a 0 and at some 250a 0 , where the H(n ) 3) and (n ) 4) dissociation curves cross. [5][6][7] These perturbations are much weaker, but should be included in more refined models of H + H -heavy Rydberg states. The above considerations imply that quantum defects in the heavy Bohr system are large, much larger than in the s-series of alkali atomic systems.…”

“…At higher excitation energies, the HH j 1 Σ g + and the B′′B j 1 Σ u + states were identified with dominant ionic character at large internuclear separation. 3,4 At even higher energies in the H 2 molecule additional electronic states of ion-pair character were predicted, 5,6 but experimental searches for bound levels are still inconclusive. 7 The photoexcitation, and the photophysics including ionization and dissociation phenomena above the ion-pair threshold have been widely investigated over the years.…”

Search for outer-well states above the ionization potential in H2

“…the potential follows the H þ -H À ion-pair curve. While the calculations of Detmer et al [8] already gave a guide for the experimentalist, Staszweska and Wolniewicz [9] recently presented a highly accurate BO-curve for the 6 1 R þ u state, adiabatic corrections, a calculation of level energies in 6 1 R þ u , and a tabulation of FranckCondon factors (FCF) for the 6 1 …”

“…The question arises whether higher lying double-well structures exist and if so, support bound states. Detmer et al [8] calculated Born-Oppenheimer potential curves of several higher lying states of 1;3 R þ g;u symmetries. These calculations predict an internal barrier behavior for the 4 1 R þ u and 5 1 R þ u states, but the 6 1 R þ u state is particularly interesting from an experimentalistÕs perspective; it contains a large barrier and an outer well part which is bound by more than 5000 cm À1 at 30-35 a.u.…”

“…1 the potential energy curves for 1 R þ u states (n P 3), relevant for this study, are reproduced from [8]. We focus on states of ungerade symmetry, because excitation schemes via lower lying states of gerade symmetry are more suitable for our experimental setup.…”