Electron paramagnetic resonance in positively charged Au_(25) molecular nanoclusters

摘要

In this study, we investigated the unpaired electrons and singly occupied molecular orbitals (SOMO) of positively charged Au_(25) molecular clusters using solid-state electron paramagnetic resonance (EPR). The EPR powder spectra of the positively charged (Au_(25) ~+) and neutral (Au_(25) ~0) species of Au_(25) are discussed and compared. Our study demonstrates that Au_(25) ~+ is paramagnetic with a SOMO that is mostly localized about the central gold atom in the core of the molecule and possesses a strong p-type atomic character. The unpaired electron spin is demonstrated to strongly interact with the nuclear spins from other ~(197)Au nuclei in the core of Au_(25) ~+ molecules and the hyperfine tensor describing such interaction was extracted from the comparison of the EPR spectra with quantum mechanical simulations assuming an anisotropic structure of the core. Our simulations suggest that the core of Au_(25) ~+ molecular clusters is more distorted than in the corresponding neutral counterpart. They also confirm previous hypotheses suggesting that the icosahedral core of Au_(25) ~+ experiences contraction with decreasing temperature.