Mass spectrometric study of molecular and ionic sublimation of lanthanum triiodide

• Lanthanum triiodide was investigated by the Knudsen effusion mass spectrometry.
• (LaI3)n molecules (n = 1–3) and [I(LaI3)n]− ions (n = 0–4) were registered in the saturated vapor.
• The sublimation enthalpy was found by the second and third law of thermodynamics.
• The enthalpies of ion-molecular reactions with cluster ions were calculated.
• The electron work function of the crystalline LaI3 was obtained.

The molecular and ionic composition of saturated vapor over lanthanum triiodide was studied by Knudsen effusion mass spectrometry. The (LaI3)n molecules (n = 1–3) and the [I(LaI3)n]− ions (n = 0–4) were observed. The partial pressures of the molecules were determined and the enthalpies of sublimation, ΔsH° (298.15 K) in kJ mol−1, in the form of monomers (304 ± 7), dimers (428 ± 25), and trimers (455 ± 50) were obtained by the second and third laws of thermodynamics. The enthalpy of formation, ΔfH° (298.15 K) in kJ mol−1, of the LaI3 (−376 ± 10), La2I6 (−932 ± 25), La3I9 (−1585 ± 50) molecules and the LaI4− (−841 ± 24), La2I7− (−1486 ± 32) ions were determined. The electron work function, φe = 3.5 ± 0.3 eV, for the LaI3 crystal was calculated from the thermochemical cycle.

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