Thermochemical study of gaseous indium-arsenic sulfosalt

Sulfide systems are often used at high temperatures, when vaporization of the components is enabled. Sulfide ores are used as sources of various metals and nonmetals and gaseous sulfides, and sulfosalts may also play a role in the atmosphere chemistry of hot rocky exoplanets. To predict the existence and thermal stability of gaseous sulfides and sulfosalts it is important to know their thermodynamic characteristics. In this study the sulfosalt of indium and arsenic was obtained in the gaseous phase for the first time.

High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over indium and arsenic sulfides. A molybdenum double two-temperature cell was used to create the conditions of coexistence of indium and arsenic sulfides. A theoretical study of gaseous As₄ S₄ and In₂ AsS₂ was performed using both B3LYP, M06, PBE0 and TPSSh hybrid DFT functionals and an ab initio wave function-based MP2(Full) method.

Gaseous In₂ AsS₂ has been identified during vaporization of In₆ S₇ and As₂ S₃ from the molybdenum double two-temperature cell. The structure and molecular parameters of gaseous In₂ AsS₂ were determined using quantum chemical calculations. Energetically favorable structures of gaseous In₂ S, AsS, As₄ S₄ and In₂ AsS₂ were found and vibrational frequencies were evaluated in the harmonic approximation. The formation enthalpy of gaseous In₂ AsS₂ (186 ± 37 kJ mol^-1 ) was derived as a result of measurements of the equilibrium constants of two independent gas-phase reactions.

The gaseous sulfosalt of indium and arsenic was obtained for the first time. The formation enthalpy of the In₂ AsS₂ (g) molecule at 298 K was evaluated both experimentally and theoretically. The thermal stability of the gaseous sulfosalt is less than that of the gaseous oxyacid salts.