The dimerization of SnCl2(g): mass spectrometric and theoretical studies

The vaporization of SnCl2(s) was investigated in the temperature range between 382 and 504 K by the use of Knudsen effusion mass spectrometry. The Sn+, SnCl+, SnCl2+, Sn2Cl3+, and Sn2Cl4+ ions were detected in the mass spectrum of the equilibrium vapor. The SnCl2(g) and Sn2Cl4(g) gaseous species were identified, and their partial pressures were determined. The structure and vibrational properties of both species and corresponding fragmentation products were studied applying density functional theory and second-order Møller-Plesset perturbation theoretical approaches. Molecular parameters yielded thermodynamic functions by the use of statistical thermodynamics. The sublimation enthalpies of SnCl2(g) and Sn2Cl4(g) at 298 K resulting from the second- and third-law methods are evaluated as 130.9 +/- 6.2 kJ mol(-1) and 155.8 +/- 7.3 kJ mol(-1), respectively. The enthalpy changes of the dissociation reactions Sn2Cl4(g) = 2 SnCl2(g) were obtained as delta(d)H degrees(298) = 106.8 +/- 6.2 kJ mol(-1). The corresponding theoretical value amounts to 103.4 kJ mol(-1). The change of monomer properties due to the dimerization reaction is also discussed.