A Study of 15 Singlet Rydberg Series of HeH and Their Correlation with the Rydberg Series of Li

Abstract

We theoretically study 37 Rydberg states of HeH derivable from the He(1s 2) + H(nl) configuration with n ≤ 5 along with three states with n = 6. The multireference configuration interaction method is used to calculate their electronic energy curves (EECs) for the internuclear distance R from 0 to 28a 0, which are regarded as the united‐atom (UA) and separated‐atoms (SA) limits, respectively. The 15 Rydberg series (nsσ, npσ, ndσ, nfσ, ngσ, ndδ, nfδ, ngδ, ngγ, npπ, ndπ, nfπ, ngπ, nfϕ, and ngϕ) are identified. Bingel's perturbation theory is used to explain the role of the core part and the Rydberg orbitals in the behavior of EECs at small R. Smith's theory of diabatization is directly solved to obtain the diabatic quantum defect curves (QDCs). From the correlations in diabatic QDCs between the UA and SA limits, the following order of orbital energies in the equilibrium region is found: npσ < nsσ < npπ < ndσ < ndπ < nfσ < nfπ < nfδ < nfϕ < ndδ, except 5dδ < 5fϕ. This order is identical to that in one‐electron molecular systems at small R, except for the nsσ and npπ series. The correlation rules are n UA = n SA + 1 for the npσ series and n UA = n SA for other series; additionally, l UA = l SA for all cases except for the 2pσ − σ1s correlation. A reversal of the diabatic dipole moment at avoided crossing points of the nsσ and npσ series is observed, and explained by the behaviors of ns and np wavefunctions of H at small R.

Transition of the Rydberg series from the spectroscopic to the united atom region in LiH

“…From the above discussion, we conclude that the core contributions to Δk 2 and Δk 3 are almost completely cancelled out in the nlλ series. According to table 4, the isotropic contribution to Δk 2 is larger than 75% and greatly contrasts to the case of HeH, where most contributions come from the anisotropic part (Kim and Lee 2016). The total Δρ 00 values are dominated by the contribution from the outer core 2s.…”

“…The sign of the dipole moment is chosen to be negative when the molecule is polarized as Li + -H − . Previous studies showed that the magnitudes of the dipole moments rapidly grow as n of the Rydberg state nlλ increases (Gim andLee 2014, Kim andLee 2016). This may be the result of an increase in the Rydberg orbital radius (n * ) 2 a 0 as n increases, where n * denotes the effective quantum number defined by n−δ nl (R), and its value is obtained by…”

“…Although electronic energy curves (EECs), E(R), are useful for oneelectron molecular systems, this is not the case for many electron molecular systems. This is derived from the dominance of a core part in the EECs that causes all EECs to look similar, hiding the characteristic behaviour of the EEC of the Rydberg orbital alone (Kim and Lee 2016). For many electron systems, most of the core contribution in E(R) may be removed by subtracting the E + (R) of the corresponding molecular ion.…”

Correlations between States in the United Atom and Separated Atoms Limits in HeH+

“…The details of the implementation are described first. Then, in order to judge the accuracy of the method, the results of the calculations are compared with those obtained by the very accurate MRCI method . We then study the correlation by numerically examining the nodal structures.…”