Molecules mimicking atoms: Monomers and dimers of Li(NH3)4 and Na(NH3)4
Isuru R. Ariyarathna, Filip Pawłowski, Joseph Vincent Ortiz, and Evangelos Miliordos
Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36849
Email: ira0002@auburn.edu
In-depth exploration is carried out for ground and excited states of Li(NH3)4 and Na(NH3)4 complexes using high level theoretical methods. Both complexes are found to be stable with respect to M(NH3)4→M(NH3)3+NH3 dissociation. The highest occupied molecular orbital in the ground state of these tetrahedral complexes are diffused around the nuclear skeleton in spherical shape (resembling an sorbital). This type of molecules can be best illustrated as an electron surrounding the [M(NH3)4] + core, mimicking the hydrogen atom. Excited states of these complexes occupy pseudo p, d, s, and p shaped orbitals. Similarly, to the previously reported Be(NH3)4 + , the observed complete shell model is 1s, 1p, 1d, 2s, and 2p. Additionally, the anionic complexes of both Li(NH3)4 and Na(NH3)4 are stabilized by 0.45 eV over their neutral species. Two such neutral monomers can bind together to make dimers. The binding energies of [Li(NH3)4]2 and [Na(NH3)4]2 dimers with respect to two monomers are 9.1 and 9.5 kcal/mol. Ground and excited states, where σ*, π, and π*-type orbitals are populated, of these dimers are further explored by constructing potential energy profiles as a function between the two monomers.