Gold chloride cluster ions generated by vacuum laser ablation

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 [AuH_r(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 [AuCl_t(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.