Ab initio electronic structure and prospects for the formation of ultracold calcium–alkali-metal-atom molecular ions

Abstract

Experiments with cold ion–atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an alkali-metal atom: CaAlk+ (Alk = Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotentials, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potential energy curves, spectroscopic constants, and transition and permanent electric dipole moments are determined and analyzed for the ground and excited electronic states. We examine the prospects for ion-neutral reactive processes and the production of molecular ions via spontaneous radiative association and laser-induced photoassociation. After that, spontaneous and stimulated blackbody radiation transition rates are calculated and used to obtain radiative lifetimes of vibrational states of the ground and first-excited electronic states. The present results pave the way for the formation and spectroscopy of calcium–alkali-metal-atom molecular ions in modern experiments with cold ion–atom mixtures.

Electronic structure, cold ion–atom elastic collision properties and possibility of laser cooling of BeCs+ molecular ion

“…For the remaining states 3 1 S + , 5 1 S + and 7 1 S + dissociating into Be + + Cs, we note significant negative permanent dipole moments in a particular region yield the same linear behavior at large distances, showing the increasing distance between the negative and positive center-of-charge. This behavior is typically observed for heteronuclear molecular ions, [34][35][36][37][38][39][40] and implies that even molecular ions in very weakly bound states have effectively a significant permanent electric dipole moment. For the permanent dipole moments of the of 3 S + , 1,3 P and 1,3 D electronic states, we get the same observation as for the permanent dipole moments of the 1 S + states.…”

Electronic Spectroscopy and Photoionization of LiMg

“…4 The bond length was found to be shorter than that of covalently bound Li 2 , in part due to the smaller covalent radius of Be. Electronic spectra for 7 Li 24 Mg, recorded by means of resonantly enhanced two-photon ionization (RE2PI), were reported by Berry and Duncan. 5 Two electronic band systems labeled E-X1 2 Σ + and F-X1 2 Σ + were observed in the 30000−32000 cm −1 range.…”

“…Over the past decade there has been additional interest in the Alk-AE dimers generated by the possibility that they may be suitable for cooling to ultracold temperatures. − An ensemble of these dimers would be able to process information by means of both electric dipole and spin–spin interactions. Molecular ions of the form Alk-AE + have closed shell 1 Σ + ground states. ,,− While they do not offer the advantages of facilitating magnetic interactions through spin, they can be trapped and manipulated using external electric fields.…”

“…There have been many theoretical and experimental studies of the Alk-AE dimers. − ,,− As the present study is focused on LiMg, we briefly summarize the gas-phase spectroscopic work that has been carried out on the Li-AE series. Electronic spectra have been recorded for LiBe, LiMg, , LiCa, ,, LiSr, ,, and LiBa. , With the exception of LiMg, a subset of the spectra for each dimer has been recorded at the level of rotational resolution.…”

“…Calculated and Measured Molecular Constants for7 Li24 Mg This is the ΔG 1/2 value computed using the program level 8.0. 58…”