The evaporation thermodynamics of lithium iodide. Mass spectrometric andab initio studies

Abstract

The vaporization of LiI was investigated in the range between 583 and 726 K by Knudsen effusion mass spectrometry (KEMS). The ionization or the appearance energies (IE or AE) of all kinds of ions formed from the equilibrium vapour over solid lithium iodide were determined using Vogt and Pascual's deconvolution method. For the determination of vapour pressure two methods, viz. mass-loss Knudsen effusion and Knudsen effusion mass spectrometry were applied. The mean natural logarithms of the equilibrium vapour pressures (in Pa) of monomer and all kinds of oligomers, that can be detected using KEMS, as a function of temperature, can be expressed as follows: ln p LiI À22240 AE 450aT 28X03 AE 0X66 between 583 and 723 K ln p Li 2 I 2 g À21940 AE 390aT 28X46 AE 0X60 between 583 and 726 K ln p Li 3 I 3 g À27300 AE 660aT 31X5 AE 1X1 between 643 and 726 K ln p Li 4 I 4 g À24820 AE 540aT 25X65 AE 0X66 between 668 and 726 K The molecular structure and the harmonic vibrational frequencies of (LiI) n species (n = 1,2,3,4) were predicted using ab initio molecular orbital methods. Both the bond dissociation energies and the enthalpy changes of dissociation of (LiI) n oligomers were evaluated and compared with the measured enthalpy change data. Using the calculated geometry and the vibration frequencies, the thermodynamic functions of (LiI) n could be calculated, making it possible to compare the second and third law thermodynamic data. # 1998 John Wiley & Sons, Ltd. Received 24 February 1998; Revised 7 May 1998; Accepted 25 May 1998 The vaporization of LiI has been previously studied by a very limited number of investigators using Knudsen effusion mass spectrometry.1-3 For the determination of the partial pressures and the thermodynamic properties of the species present in the equilibrium vapour over condensed LiI, as a first step, the assignment of the ions formed by electron impact has to be determined. Literature values for ionization (IE) and appearance energies (AE) can be found in the articles of Friedman 1 and Platel, 4 but appropriate values for tetrameric ions have not been determined so far. The latter authors determined the values of IE and of AE using the vanishing current and linear extrapolation methods, respectively. We have shown in several articles [5][6][7] that linear extrapolation is not a suitable method in most cases. Instead of linear extrapolation Vogt and Pascual's deconvolution method 8 was applied in the present study. Since the determination of ionization and appearance energies does not provide quantitative information concerning the neutral precursors of the ions, Gorokhov 2 and Berkowitz et al.3 used a double-oven Knudsen apparatus for the apportionment of the total ion currents. A double-oven Knudsen apparatus was first used by Miller and Kusch. 9 Milne 10 derived a relationship for the determination of the relative cross section of a dimeric molecule to that of a monomeric one, assuming chemical equilibrium in the gas phase and viscous flow between the two compartments of the cell (the mea...

Molecular Structure of Metal Halides

“…15,60,79,80 Vibrational spectroscopic studies have also identified dimers and larger associates in their vapors. 25,81 Dimers were also registered by recent ED studies, and their geometries were determined.…”

Study of vaporization of LiI, LiI/C70, LiI/LiF/C70 from the Knudsen cell located into ionization chamber of the mass spectrometer

“…6 In the present work, it is difficult to assume exclusively precursors of Li n I + (n = 2, 3, 4 and 6) clusters, based on the results presented in Fig. 6 In the present work, it is difficult to assume exclusively precursors of Li n I + (n = 2, 3, 4 and 6) clusters, based on the results presented in Fig.…”

“…6 The results obtained in the present study are compared in Table I with those obtained by other researchers. 6 The results obtained in the present study are compared in Table I with those obtained by other researchers.…”

“…6 This indicates that the experimental setup in which the Knudsen cell is placed in the ionization chamber provides an efficient way to detect all of the above-mentioned ions. 6 This indicates that the experimental setup in which the Knudsen cell is placed in the ionization chamber provides an efficient way to detect all of the above-mentioned ions.…”

“…[6][7][8][9][10] Especially, lithium homogenous clusters have received great attention from physicists and chemists as prototypes for the investigation of the properties of metallic clusters. Studies on metallic clusters are of considerable interest in research due to their potential application in catalytic processes, materials science, biology, and medicine.…”