Probing the interactions of O(2) with small gold cluster anions (Au(n)(-), n = 1-7): chemisorption vs physisorption.
Activation of O(2) is the most critical step in catalytic oxidation reactions involving gold and remains poorly understood. Here we report a systematic investigation of the interactions between O(2) and small gold cluster anions Au(n)(-) (n = 1-7) using photoelectron spectroscopy. Higher resolution photoelectron spectra are obtained for the molecularly chemisorbed even-sized Au(n)O(2)(-) (n = 2, 4, 6) complexes. Well-resolved vibrational structures due to O-O stretching are observed and can be readily distinguished from the Au-derived PES bands. The adiabatic detachment energies and O-O vibrational frequencies are measured to be 3.03 +/- 0.04, 3.53 +/- 0.05, and 3.17 +/- 0.05 eV, and 1360 +/- 80, 1360 +/- 80, and 1330 +/- 80 cm(-1) for n = 2, 4, 6, respectively. Physisorbed Au(n)(-)(O(2)) complexes for n = 1, 3, 5, 7 are observed for the first time, providing direct evidence for the inertness of the closed-shell odd-sized Au(n)(-) clusters toward O(2). Neutral even-sized Au(n) clusters are closed-shell and are expected to be inert toward O(2), which is not consistent with the reduced O-O vibrational frequencies observed in the photoelectron spectra relative to free O(2). It is suggested that the photodetachment transitions can only access excited states of the neutral even-sized Au(n)O(2) complexes; a double-well potential is proposed consisting of the ground-state van der Walls well at long Au(n)-O(2) distances and a higher energy deeper well at short Au(n)-O(2) distances derived from singlet O(2) ((1)Delta(g)). The current study provides further insight into O(2) interactions with small gold clusters, as well as accurate experimental data to benchmark theoretical investigations.
Huang
Wei
W
Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
Zhai
Hua-Jin
HJ
Wang
Lai-Sheng
LS