Photoelectron spectroscopy and theoretical study of AlnC5−/0 (n = 1–5) clusters: structural evolution, relative stability of star-like clusters, and planar tetracoordinate carbon structures

Abstract

The Al_nC₅⁻ (n = 1–5) clusters were detected in the gas-phase and were investigated via mass-selected anion photoelectron spectroscopy. The structures of Al_nC₅^−/0 (n = 1–5) were explored by theoretical calculations. It is found that the structures of AlC₅^−/0 and Al₂C₅^−/0 are linear while those of Al₃C₅^−/0, Al₄C₅^−/0, and Al₅C₅^−/0 are two-dimensional. The most stable structures of AlC₅^−/0 and Al₂C₅^−/0 are linear with the Al atoms attached to the ends of C₅ chain. The most stable structures of Al₃C₅^−/0 can be viewed as three Al atoms interacting with a nonlinear C₅ chain. The most stable structure of Al₄C₅⁻ anion is a planar structure composed of a C₂ unit, a C₃ unit, and two Al₂ units, while that of the neutral Al₄C₅ cluster has four Al atoms connected to different positions of a distorted C₅ chain. The global minimum structures of Al₅C₅^−/0 are planar structures composed of an Al₄C quadrilateral, two C₂ groups, and an Al atom connected to two C₂ groups. Planar tetracoordinate carbon (ptC) has been identified in the structures of both anionic and neutral Al₅C₅. It is worth mentioning that the star-like structure of Al₅C₅⁻ is slightly higher in energy than the ground state structure. The comparison of theoretical calculations with the experimental spectra indicates the star-like structure of Al₅C₅⁻ may also appear in our experiments.