Gold chloride cluster ions generated by vacuum laser ablation

摘要

In this work, a simple way for study the possibility of formation a vapor cluster species of tetrachloroauric acid (HAuCl4), using the laser ablation in the absence of a buffer or reactive atmosphere, and without a postablation supersonic expansion on a commercial matrix assisted laser desorption/ionization time-of-flight mass spectrometer, is reported. Tetrachloroauric acid is known as precursor for the synthesis of gold nanostructures and the complex salts; therefore it is an important task to discover and quantify the species arising from HAuCl4, in order to understand their role in the gold assisted reactions. Mass spectrum of HAuCl4 in a reflector negative-ion mode contains the hydrated mono- and dinuclear gold clusters in the m/z range 286-436, and gold chloride clusters in the m/z range 447-795. In the first part of spectrum, m/z range 286-436, the hydrated gold cluster species of type Au-n(-)(H2O)(m) (n = 1-2; m = 1, 2, 5, 7, 8) and [Au-n(OH)(k)](-)(H2O)(m) (n = 1-2; k = 1-2; m = 1, 4-8) were found. Besides that, there are gold chloride clusters with general formula [AuHr(HCl)(2)](-)(H2O)(m) (m = 1-5; 8-9; r = 0-2) in this part of spectrum. In the second part of spectrum, the m/z range 447-795, only gold chloride clusters were obtained. Their general formulae can be written as [AuClt(HCl)(v)](-)(H2O)(m) (t = 1-4; v = 5-8; m = 2-4, 6-8) and [Au-n(HCl)(v)](-)(H2O)(m) (n = 1-2, v = 4-5, m = 1-2, 5, 7). The analysis of concentration effects on the LDI mass spectra of gold clusters reveals that the relative intensities of signals for the mono- and dinuclear Au clusters increase with decreasing the concentration of water HAuCl4 solutions.