PNNL

Abstract

We report vibrationally-resolved photoelectron spectroscopy (PES) of Au2(CO)n- (n = 1-3), in combination with relativistic density functional theory (DFT) and ab initio calculations. The ground state transition in the spectrum of Au2CO- is broad, containing vibrational structures both in the bending and CO stretching modes and suggesting a large structural change from Au2CO- to Au2CO. The ground state transitions for both n = 2 and 3 display a well resolved vibrational progression in the CO stretching mode with frequencies of 2110 - 40 and 2160 - 40 cm-1, respectively. The PES data show that chemisorption of the first two CO’s each induces a significant red-shift in the electron binding energies. The third CO is physisorbed, inducing only a slight increase in electron binding energies relative to Au2(CO)2-. Relativistic DFT and ab initio calculations are performed to determine the ground-state structures for Au2(CO)n- and Au2(CO)n and the results agree well with the experiment. Au2(CO), Au2(CO)2, and Au2(CO)2- are all found to be linear, while Au2(CO)-- is bent due to the Renner-Teller effect. A strong spin-orbit effect is found in Au2(CO)2- that quenches the Renner-Teller effect, keeping the linear structure for this anion. The physisorption in Au2(CO)3- is borne out in CCSD(T) calculations. However, a wide range of DFT methods used fail to correctly predict the relative energies of physisorbed versus chemisorbed isomers for Au2(CO)3-.