The geometric and electronic structures of Arn+ (n=3–27)

Abstract
The most stable structures of Arn+, n=3–27, are determined with the analytical gradient method for the diatomics‐in‐molecules Hamiltonian. The oscillator strength distribution is evaluated. The charge is found to be localized on the central three atoms, which form the trimeric ion core. The first solvation shell evolves around the ion core and is completed at n=25. The calculation shows that the photoabsorption band is in the visible region, which originates from the 2Σu+2Σg+ transition of the Ar3+ ion core, and is red‐shifted with the increase of the cluster size, reproducing the experimental results. The red‐shift is explained in terms of the solvated ion core model, in which the excited state of the ion core interacts strongly with the surrounding solvent atoms.