First Evidence of Rhombic (NaCl)₂^‐. Ab initio Reexamination of the Sodium Chloride Dimer Anion.

Abstract

The possibility of electron binding to sodium chloride dimers in the gas-phase was studied at the coupled cluster level with single, double, and noniterative triple excitations using aug-cc-pVDZ+6s6p4d basis sets. It was found that three kinds of anions can be formedsquasi-linear dipole-bound, nearly rhombic quadrupolebound, and linear solvated-electron anions. In contrast to the earlier results, it was found that the rhombic neutral dimer (which is the neutral global minimum) does bind an excess electron to form an electronically stable anion of quadrupole nature. The global minimum on the ground-state anionic potential energy surface corresponds to the dipole-bound anion of quasi-linear structure (NaCl‚‚‚NaCl) -whose vertical electron binding energy is 12 051 cm -1 . It was also found that solvated-electron structure (ClNa‚‚‚NaCl) -is considerably higher in energy than the anionic global minimum but its vertical electron detachment energy is significantly larger (i.e., 21 306 cm -1 ). The nearly rhombic (NaCl) 2 -lies only 0.181 eV above the anionic global minimum but below the global minimum of the neutral species.

Prediction of a Non-Valence Temporary Anion State of (NaCl)2

“…We also checked that it remains close to optimal for q = −0.07 where the B 2u anion is temporary with the highest energy found in this study. This basis set gives a KT value of the vertical EBE (for forming the A g anion) of 20 meV, 3 meV smaller than that reported by Anusiewicz et al 19 Moreover, the EA-EOM-CCSD value of the EBE from our calculations (139 meV) employing this basis set and the FC approximation agrees closely with the EA-EOM-CCSD result of Sommerfeld et al 20 As noted above, we have also calculated the EBEs as a function of q, the extent of the displacement along the normal coordinate corresponding to the totally symmetric breathing mode of the neutral molecule. As q is varied, the location of the supplemental diffuse s functions relative to the sodium atoms was held fixed, displaced 5 Å from the Na atoms.…”

“…Distortion along the totally symmetric breathing mode (q) was considered in order to follow the B 2u anion as it evolves from a bound state to a TA, with a value of q = 0 corresponding to the optimized geometry of the neutral cluster. The FC approximation was used in previous studies, 19,20 and the geometries considered in the current work are largely based on the geometry and definition of q given above. However, in the course of this work, it became apparent that correlating the 2s and 2p electrons in the sodium atoms had a significant effect on the optimized geometry of the neutral cluster and on the energies of the anion states relative to the neutral.…”

“…This consideration suggests that the rhombic (NaCl) 2 cluster is an ideal candidate for a non-valence temporary anion, as it has been predicted to have a bound non-valence anion state of A g symmetry. 19,20 In the study of Anusiewicz et al, 19 (NaCl) 2 was reported to have a vertical electron binding energy (EBE) of 23 and 144 meV at the KT and coupled cluster singles and doubles with perturbative triples [CCSD-(T)] 21 levels of theory, respectively. (In the sign convention used in the present study, a positive EBE refers to a bound anion.)…”

Structures and Electronic Properties of (KI)n–/0 (n = 1–4) and K(KI)n–/0 (n = 1–3) Clusters: Photoelectron Spectroscopy, Isomer-Depletion, and ab Initio Calculations

“…This structure is quite different from the ground state structure of its anionic counterpart 22A-I, which is quasi-linear as described above. According to the previous studies on (NaCl) 2 − , 29,30 when the excess electron was added to the rhombus (NaCl) 2 , the structure may rearrange into quasi-linear configuration by overcoming a small kinetic barrier of 0.108 eV (2.49 kcal/mol), due to the balance between the strength of the electron binding to the cluster and the coulomb repulsion between the neutral NaCl molecules. The case of (KI) 2 −/0 should be similar as that of (NaCl) 2 −/0 .…”

“…The low VDE of isomer 22A-II is similar to the previous theoretical calculations on the rhombus structure of (NaCl) 2 − , which found the rhombus structure of (NaCl) 2 − has a low VDE of about 1270 cm −1 (∼0.16 eV). 29,30 Similarly, the VDE of the rhombus structure of (KCl) 2…”