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The L-tryptophan sublimation was studied by high-temperature mass spectrometry in the temperature range 395–493 K. The compound evaporates congruently in the form of monomeric molecules. The saturated vapor pressure at 485 K was determined by the Knudsen effusion method. In combination with mass spectrometric data, the pressure equation ln (p, Pa) = –(19943±304)/T + (40.568±0.688) is recommended for the temperature range 395–493 K. The enthalpy of 167.5±1.6 kJ/mol for sublimation at 298.15 K was determined on the basis of the second and third laws of thermodynamics.

In the temperature range of 388–506 K in saturated vapor over 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImTfO) ionic liquid along with the monomer neutral ionic pairs (NIP) C+A–, where C+ is EMIm+ (cation) and A– is TfO– (anion), the dimers (C+A–)2 were registered with a fraction of 0.5% for the first time. The corresponding associative ions C2A+ and C3A2+ formed as a result of attachment of the cation C+ to the monomer and dimer NIPs were also found. The evaporation enthalpies ΔvH°(298.15 K) = 128 ± 5 kJ mol–1 (monomer) and ΔvH°(298.15 K) = 161 ± 9 kJ mol–1 (dimer) were determined. The enthalpy of formation of the monomer and dimer NIP of EMImTfO at 298.15 K in the state of ideal gas were derived from the evaporation enthalpies: –1033 ± 50 kJ mol–1 and –2160 ± 50 kJ mol–1, respectively. The desorption enthalpies ΔdesH°(T) of the C+, C2A+, and C3A2+ cations were found to be 164 ± 5 kJ mol–1 (435 K), 159 ± 7 kJ mol–1 (435 K), and 152 ± 21 kJ mol–1(457 K), respectively. The equilibrium constants of the heterophase ion-molecular reactions were measured and the formation enthalpies of associative ions were calculated: ΔfH°(C2A+, 298.15 K) = –493 ± 50 kJ mol–1 and ΔfH°(C3A2+, 298.15 K) = –1631 ± 50 kJ mol–1.

Ion-molecular equilibria LaI4– + LnI3 = LnI4– + LaI3, Ln2I7– = LnI3,cr + LnI4– (Ln = Ce, Pr, Gd, Tb, Tm, and Lu), and 3LaBr4– + 4LaI3 = 3LaI4– + 4LaBr3 in vapors over the LaI3-CeI3-PrI3-GdI3, LaI3-GdI3-TbI3-TmI3, and LaI3-LaBr3 mixtures and the pure lanthanide triiodides were studied in the temperature range of 700–1050 K by Knudsen effusion mass spectrometry. The equilibrium constants were measured and the reaction enthalpies were calculated by the techniques of the second and third laws of thermodynamics. The standard formation enthalpies of ions, ΔfH°(298.15 K) (in kJ mol–1), were determined to be –832 ± 21 (LaI4–), –834 ± 23 (CeI4–), –834 ± 25 (PrI4–), –812 ± 24 (GdI4–), –813 ± 25 (TbI4–), –817 ± 23 (TmI4–), –806 ± 25 (LuI4–), –1399 ± 45 (La2I7–), –1402 ± 46 (Ce2I7–), –1417 ± 47 (Pr2I7–), –1356 ± 47 (Gd2I7–), –1365 ± 47 (Tb2I7–), –1366 ± 46 (Tm2I7–), and –1322 ± 47 (Lu2I7–).

Sublimation of 1,3,3,6′-tetramethyl-8′-formyl-spiroindoline-2,2′-[2H] -chromene (SP-1) and 3,6′-dimethyl-8′-formyl-spiro (4-oxo-3,4-dihydro-2H-1,3-benzoxazine)-2,2′-[2H] -chromene (SP-2) was studied by Knudsen effusion mass spectrometry in the temperature range 309–363 K and 331–384 K, respectively. It has been shown that, in the temperature range under study, both spiropyrans are thermally stable and sublime congruently in the form of monomeric molecules. The dependences of the saturated vapor pressure (Pa) on temperature are described by the equations: lg p (SP-1) = – (6.239±0.093)∙103∙T–1+ (15.832±0.278), lg p (SP-2) = – (6.625±0.111)∙103∙T–1 + (15.459±0.312). The sublimation enthalpies have been evaluated by the second law method as ΔsH°(298.15 K) = 119±5 kJ∙mol–1 (SP-1) and ΔsH°(298.15 K) = 128±5 kJ∙mol–1 (SP-2). The enthalpies of formation of spiropyran molecules in the ideal gas state, ΔfH°g(298.15 K) = 199±9 kJ∙mol–1 (SP-1) and ΔfH°g(298.15 K) = –296±10 kJ∙mol–1 (SP-2), have been calculated using isodesmic reactions method implying quantum chemical calculations. Combining the latter values with the corresponding sublimation enthalpies the enthalpies of formation for crystalline state spiropyrans were determined: ΔfH°cr(298.15 K) = 80±10 kJ∙mol–1 (SP-1) and ΔfH°cr(298.15 K) = –424±11 kJ∙mol–1 (SP-2).

A multi-technique approach based on Knudsen effusion mass spectrometry, gas phase chromatography, mass spectrometry, NMR and IR spectroscopy, thermal analysis, and quantum-chemical calculations was used to study the evaporation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4). The saturated vapor over BMImBF4 was shown to have a complex composition which consisted of the neutral ion pairs (NIPs) [BMIm+][BF4−], imidazole-2-ylidene C8N2H14BF3, 1-methylimidazole C4N2H6, 1-butene C4H8, hydrogen fluoride HF, and boron trifluoride BF3. The vapor composition strongly depends on the evaporation conditions, shifting from congruent evaporation in the form of NIP under Langmuir conditions (open surface) to primary evaporation in the form of decomposition products under equilibrium conditions (Knudsen cell). Decomposition into imidazole-2-ylidene and HF is preferred. The vapor composition of BMImBF4 is temperature-depended as well: the fraction ratio of [BMIm+][BF4−] NIPs to decomposition products decreased by about a factor of three in the temperature range from 450 K to 510 K.

The results of systematic investigations of the molecular and ionic sublimation of lanthanide triiodides LnI3 (Ln = La–Lu) by Knudsen effusion mass spectrometry are summarized. The LnI3 monomer and Ln2I6 dimer molecules as well as the associated LnI4– and Ln2I7– ions are the main constituents of saturated vapor. The total fraction of ions is negligible compared to that of neutral species. The partial vapor pressures of the molecules and the equilibrium constants of ion-molecular reactions are determined. On the basis of a joint analysis of all vaporization thermodynamics data obtained in the period from 1952 to 2020, the sublimation enthalpies ΔsHo(298.15 K) of LnI3 in the form of monomer and dimer molecules are recommended. The standard thermochemical properties such as the formation enthalpy and atomization/dissociation enthalpy of the molecules and ions are obtained. The variation of these properties along the lanthanide series is discussed.

The sublimation of solid gadolinium and thulium triiodides was studied by Knudsen effusion mass spectrometry. The partial vapor pressures [atm] of the monomer and dimer molecules were determined as: ln p (GdI 3 ) = −(32.31 ± 0.18) × 10 3 / T + (21.38 ± 0.21) for 777–946 K; ln p (Gd 2 I 6 ) = −(38.07 ± 0.42) × 10 3 / T + (24.49 ± 0.47) for 843–946 K; ln p (TmI 3 ) = −(31.84 ± 0.25) × 10 3 / T + (21.88 ± 0.29) for 760–965 K; and ln p (Tm 2 I 6 ) = −(38.23 ± 0.27) × 10 3 / T + (25.71 ± 0.43) for 799–965 K. In addition, the trimers Gd 3 I 9 and Tm 3 I 9 were detected in very small fractions. On the basis of a joint analysis of all available data in literature, the sublimation enthalpies [kJ mol −1 ] at 298.15 K are recommended as 283 ± 9 (GdI 3 ), 336 ± 16 (Gd 2 I 6 ), 366 ± 50 (Gd 3 I 9 ), 276 ± 3 (TmI 3 ), 330 ± 6 (Tm 2 I 6 ), and 354 ± 50 (Tm 3 I 9 ). The standard formation enthalpies [kJ mol −1 ] of the gaseous species at 298.15 K are −341 ± 9 (GdI 3 ), −912 ± 16 (Gd 2 I 6 ), −1506 ± 50 (Gd 3 I 9 ), −344 ± 5 (TmI 3 ), −909 ± 7 (Tm 2 I 6 ), and −1506 ± 50 (Tm 3 I 9 ).

A mass spectrometric method for the determination of the electron work function based on analysis of thermochemical cycles including molecules and ions has been described. Application of this method for calculation of the electron work functions of lanthanum, cerium, and praseodymium triiodides gave 3.8±0.3 eV for LaI3, 3.5±0.3 eV for CeI3, and 2.8±0.3 eV for PrI3.

This work was supported by the Ministry of science and higher education of the Russian Federation in the framework of Government order (№ FZZW-2020-0007). The authors are grateful to Ph.D. N.L. Pechnikova and Dr. V.V. Aleksandriiskii (Research Sharing Center of the Ivanovo State University of Chemistry and Technology) for the synthesis of TPP and the study of the NMR spectrum, respectively, Ph.D. D.V. Tyurin (Department of Chemistry and Technology of Higher Molecular Compounds of the Ivanovo State University of Chemistry and Technology) for the MALDI spectrum of TPP and Ph.D. A.A. Gushchin (Department of Industrial Ecology of the Ivanovo State University of Chemistry and Technology) for the analysis of TPP sample by the high performance liquid chromatography. The authors also thank Ph.D. M.S. Gruzdev (Research Sharing Center of the Institute of Solution Chemistry RAS, Ivanovo) and Ph.D. D.N. Sergeev (Forschungszentrum Julich, IEK-2, Germany) for measuring the heat capacity of TPP in the temperature ranges 169–302 K and 328–568 K, respectively.

The molecular and ionic sublimation of neodymium, dysprosium, holmium, and erbium triiodides was studied by Knudsen effusion mass spectrometry. The monomer LnI3, dimer Ln2I6, and trimer Ln3I9 molecules and the ions LnI4– and Ln2I7– were found to be constituents of the saturated vapors in each case. The partial pressures of the vapor species and the equilibrium constants of the ion-molecular reactions were calculated. On the basis of a joint analysis of all literature data, the sublimation enthalpies ΔsHo(298.15 K)/(kJ mol−1) are recommended as 293 ± 3 (NdI3), 387 ± 30 (Nd2I6), 281 ± 3 (DyI3), 353 ± 12 (Dy2I6), 281 ± 3 (HoI3), 352 ± 6 (Ho2I6), 278 ± 4 (ErI3), and 350 ± 30 (Er2I6). The standard formation enthalpies ΔfHo(298.15 K)/(kJ mol−1) of the molecules and ions were determined to be −346 ± 5 (NdI3), −891 ± 30 (Nd2I6), −815 ± 23 (NdI4–), −1379 ± 46 (Nd2I7–), −336 ± 4 (DyI3), −880 ± 12 (Dy2I6), −811 ± 23 (DyI4–), −1360 ± 46 (Dy2I7–), −342 ± 4 (HoI3), −894 ± 7 (Ho2I6), −814 ± 23 (HoI4–), −1372 ± 46 (Ho2I7–), −341 ± 5 (ErI3), −888 ± 30 (Er2I6), −819 ± 23 (ErI4–), and −1377 ± 46 (Er2I7–).

The Sm, Eu, and Yb tri- and dichlorides were investigated by Knudsen effusion mass spectrometry. It was found out by the analysis of mass spectra and ionization efficiency curves that the vapor composition is complex due to the partial high temperature decomposition/disproportionation of the samples. Up to five vapor species were identified for both LnCl3 (LnCl3, LnCl2, Ln2Cl4, Ln2Cl5, and Ln2Cl6) and LnCl2 (LnCl3, LnCl2, LnCl, Ln, and Ln2Cl4). The quantitative evaluation of vapor composition was made. It indicates that the disproportionation of SmCl2 and EuCl2 is negligible in the temperature range studied whereas that of YbCl2 and the decomposition of SmCl3 and YbCl3 cannot be neglected.

The gas phase equilibria Ba + LnX = BaX + Ln (Ln = Sm, Eu, Yb; X = Cl, Br, I) were investigated by Knudsen effusion mass spectrometry using a low energy of ionizing electrons to avoid fragmentation processes. The BaX molecules were used as references with well-established bond energies. The atomization enthalpies ΔatH0° of the LnX molecules were determined to be 427 ± 9 (SmCl), 409 ± 9 (EuCl), 366 ± 9 (YbCl), 360 ± 10 (SmBr), 356 ± 13 (EuBr), 316 ± 9 (YbBr), 317 ± 10 (SmI), 293 ± 10 (EuI), and 283 ± 10 (YbI) kJ·mol−1.

The molecular and ionic composition of vapor over EMImNTf2 ionic liquid was studied by Knudsen effusion mass spectrometry. Along with the neutral ionic pairs the positive C+, C2A+, and negative A−, CA2− ions (where C+ is the EMIm+ cation and A− the NTf2− anion) were observed under equilibrium conditions for the first time. The total fraction of ionic vapor species was found to be 10− 9–10− 11 in the temperature range of 437–519 K.

a b s t r a c t A new approach based on the extrapolated difference technique was applied to determine the ion appear- ance energies of ytterbium diiodide molecules for the first time. The calibration of the mass spectrometer has been carried out with Ba and Eu atoms and showed a high accuracy determination of their ion appear- ance energies. The energy characteristics of ytterbium mono- and diiodide molecules and ions, such as the atomization energies Eat(YbI) = 2.70 ± 0.20 eV, Eat(YbI2) = 5.92 ± 0.12 eV and the dissociation energies D0(YbI + ) = 2.78 ± 0.18 eV, D0(YbI2 +

The Ln−LnI3 (Ln = La, Ce) systems and their individual components LaI3 and CeI3 have been studied by the Knudsen effusion mass spectrometry (KEMS). Monomer LnI2, LnI3, dimmer Ln2I6 molecules and positive and negative ions have been identified in the saturated vapor over these systems. The formation of LnI2 in the Ln−LnI3 systems during high temperature experiments has been determined.

An approach for the determination of atomization energies based on the extrapolated difference technique in the framework of Knudsen effusion mass spectrometry is proposed. Its essence is the use of thermodynamic data for the determination of the appearance energy of fragment ions of a reference and a special mathematical treatment of the ionization efficiency functions. The advantages of this approach are demonstrated for the cases of incongruently vaporizing lanthanide bromides that suffer from decomposition or disproportionation at high temperatures. The atomization energies for SmBr2 (7.78 ± 0.12 eV), EuBr2 (7.51 ± 0.11 eV), YbBr2 (7.25 ± 0.13 eV), SmBr3 (11.09 ± 0.10 eV), and YbBr3 (10.23 ± 0.09 eV) molecules have been determined for the first time.

RATIONALE The vaporization of Sm, Eu, and Yb tri- and dibromides is accompanied by decomposition and disproportionation reactions. These result in complex vapor compositions whose analysis is an intricate problem for experimentalists. Approaches have been developed to interpret mass spectra and accurately determine the vapor composition of thermally unstable compounds. METHODS A sector type magnet instrument was used. A combined ion source allowed the study of both the molecular and ionic vapor compositions in the electron ionization (EI) and the thermionic emission (TE) modes. The methodological approaches were based on a joint analysis of the ionization efficiency functions, the temperature and time dependences of the ion currents, and special mathematical data evaluation. RESULTS The vaporization of SmBr3, YbBr3, SmBr2, EuBr2, and YbBr2 was studied in the temperature range of 850–1300 K. An initial stage of incongruent vaporization was observed in the case of the tribromides, SmBr2, and YbBr2. This eventually changed to a congruent vaporization stage. Various neutral (Ln, Br, Br2, LnBr, LnBr2, LnBr3, Ln2Br4, Ln2Br5, and Ln2Br6) and charged (Br–, LnBr3–, LnBr4–) species were detected at different vaporization stages. CONCLUSIONS The quantitative vapor composition of Sm, Eu, and Yb tri- and dibromides was determined. It was found that only EuBr2 was stable in the studied temperature range. The developed approaches can be useful in the case of other thermally unstable compounds.

The vaporization of Al-Dy-O mixtures has been investigated by the Knudsen effusion mass spectrometry technique. The saturated vapor has been found to consist of the atoms Al, O and the molecules AlO, Al2O, DyO. At the initial stage the vaporization of Dy2O3 and Al2O3-Dy2O3 mixtures was found to be incongruent and accompanied by some loss of oxygen. An attainment of congruently vaporizing composition and equilibrium state takes quite a long time. The activities of binary oxides have been measured at T = 2130 K. The Gibbs energies and enthalpies have been derived for formation of the compounds Dy4Al2O9, DyAlO3 and Dy3Al5O12 from sesquioxides.

Geometrical structure, vibration spectra, and enthalpies of dissociation have been investigated for the ions BaCl3−, Ba2Cl3+, Ba3Cl5+, and Ba4Cl7+ which were detected earlier in the saturated vapour over BaCl2. Quantum chemical methods of density functional theory, the second and the fourth order Moller–Plesset perturbation theory have been applied. The effective core potential with cc-pVTZ basis set for barium atom and two full-electron basis sets including the diffuse and polarised basis functions for chlorine atom were used. The effect of the basis set size and the computation method on the results was analysed. According to the results, all the ions possess the compact shaped structure. The equilibrium geometrical structures were found as follows: the planar D3h for BaCl3−, triple bridged bipyramidal D3h for Ba2Cl3+, hexabridged D3h for Ba3Cl5+, and septuple bridged C2v for Ba4Cl7+. For positive ions, the different isomeric structures were considered, but no isomers for these ions have been found. The...

The molecular and ionic composition of vapor over cerium triiodide was studied by Knudsen effusion mass spectrometry. In the saturated vapor over CeI3the monomer, dimer, and trimer molecules and the negative ions I−,CeI4-, andCe2I7-were identified in the temperature range of 753–994 K. The partial pressures of CeI3, Ce2I6, and Ce3I9were determined and the enthalpies of sublimation,ΔsH°(298.15 K) in kJ·mol−1, in the form of monomers (298±9), dimers (415±30), and trimers (423±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 CeI3(-371±9), Ce2I6(-924±30), and Ce3I9(-1585±50) molecules and theCeI4-(-857±19) andCe2I7-(-1451±50) ions were calculated. The electron work function,φe=3.3±0.3 eV, for the CeI3crystal was evaluated.

The Knudsen effusion cell mass spectrometry and the density functional theory were used to study vapor species over the NaBr−LnBr3 (Ln = La, Lu) binary systems. The complex molecules NaLnBr4, Na2LnBr5 and both positive Na2LnBr4+, Na3LnBr5+ and negative NaLnBr5− complex ions have been observed in saturated vapor in the temperature range 870 - 1184 K (La) and 812 - 1065 К (Lu) for the first time along with the molecules and ions inherent to the pure components. Molecular parameters and energy characteristics were obtained by quantum-chemical calculations. The partial vapor pressures of neutral constituents have been obtained. The equilibrium constants of dissociation reactions of molecular and charged complexes were determined and the enthalpies of reactions have been calculated using the second and third laws of thermodynamics. Also the enthalpies of formation of complex molecules and ions have been obtained.

A new complex approach to determine absolute partial pressures of molecular and ionic components of vapor is advanced on the basis of a combination of mass-spectrometric and quantum-chemical methods using sodium bromide as an example. Thermodynamic parameters of molecules and ions and the electron work function are determined for crystalline NaBr.

The vaporization of Al–Dy–O mixtures has been investigated by the Knudsen effusion mass spectrometry technique. The saturated vapor has been found to consist of the atoms Al, O and the molecules AlO, Al 2 O, DyO. At the initial stage the vaporization of Dy 2 O 3 and Al 2 O 3 –Dy 2 O 3 mixtures was found to be incongruent and accompanied by some loss of oxygen. An attainment of congruently vaporizing composition and equilibrium state takes quite a long time. The activities of binary oxides have been measured at T = 2130 K. The Gibbs energies and enthalpies have been derived for formation of the compounds Dy 4 Al 2 O 9 , DyAlO 3 and Dy 3 Al 5 O 12 from sesquioxides.

Thermochemical cycles including experimentally measured enthalpies of sublimation of alkali metal halides in the form of M2X+ and MX2∮ ionic clusters and MX molecules were used to calculate work functions for NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, and RbI.

Spiropyrans are heterocyclic organic compounds known for their photochromic properties which are of perspective use for technology. They can be potentially used as the elements of molecular machines, optical data recording, modulated light filters and numerous hybrid materials. The key characteristic of such compounds is an ability to enter a photochromic reaction, taking place upon irradiation with UV light (see Figures 1 and 2). To develop more compounds which can possibly be of practical use the most important problem is to investigate their chemical properties both theoretically and experimentally. To determine the optimal geometric structures for both spiro- and mesocyanine forms of 1,3,3,6’-tetramethyl-8’-formylsporoindoline-2,2’-[2H]-chromene-3 and 3,8’-dimethyl-6’formylspiro-(-4-oxo-3,4-dihydro-2H-1,3)-benzoxasine-2,2’-[2H]-chromene-7 (objects 1 and 2 respectively) using the DFT approach, calculations of quantum chemistry were used. All the computations were carried out in GAMESS software. In this research we used B3LYP, CAM-B3LYP, wB97, M11 and TPSSh functionals in conjunction with 6-311++G(d,p) basis set. In our studies we were able to compare experimental gas-phase IR spectra with the quantum-chemically computed one. This allowed us to consider the TPSSh functional as the best model for these compounds due to the most accurate geometrical structures and thermodynamic functions obtained with its use. In addition, it was possible to compute the photoinduced products of the isomerization reaction (see Figure) of our objects and their UV/Vis spectra which were also compared with the experimental spectra of thin films. Comparison allowed us to consider high accuracy of computed data. However, an attempt to find the optimal molecular structure for the cis-isomer of the second object was unsuccessful. Except for the B3LYP functional, none of the listed above could provide us with the reliable structure and, therefore, other properties. For this reason, it was only possible to compute the reliable reaction enthalpies for the one precursor molecule. The reaction enthalpies listed in the Table 1 are considered to be optimal for using such a compound as a photosensitive switch element because it is bigger than 10 kJ/mole but no more than 100 kJ/mole. From this it follows, that spontaneous switching probability is acceptably small, although at the same time such an amount of energy is practically feasible. Reaction ∆r H(298.15 K), kJ/mol 1 56.39 2 -11.78 3 -68.17 References: S. Lukyanov and M. B. Lukyanova, Chemistry of Heterocyclic Compounds, Vol. 41, No. 3, 2005. "General Atomic and Molecular Electronic Structure System" M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. Su, T. L. Windus, M. Dupuis, J. A. Montgomery Comput. Chem., 14, 1347-1363(1993). "Advances in electronic structure theory: GAMESS a decade later" M. S. Gordon, M. W. Schmidt pp. 1167-1189, in "Theory and Applications of Computational Chemistry: the first forty years" C. E. Dykstra, G. Frenking, K. S. Kim, G. E. Scuseria (editors), Elsevier, Amsterdam, 2005. Figure 1

Nonempirical methods are used to calculate the geometric parameters, the frequencies of normal vibrations, and thermochemical characteristics of ions existing in saturated vapors over sodium bromide and iodide: Na2X+, NaX2−, Na3X2+, and Na2X3− (X = Br, I). According to the calculations, Na2X+ and NaX2− triatomic ions have a linear equilibrium configuration of D∞h symmetry. Pentaatomic ions can exist in the form of three isomers: linear with D∞h symmetry, planar cyclic with C2v symmetry, and bipyramidal with D3h symmetry. At a temperature of ∼1000 K, Na3X2+ and NaX3− pentaatomic ions are shown to be present in vapor mainly in the form of linear isomers. The energies and enthalpies of ion molecular reactions with the participation of the above ions are calculated, and the formation enthalpies of the ions are determined, ΔfHo(0 K): 293±2 kJ/mol (Na2Br+), 354±2 kJ/mol (Na2I+), −536±2 kJ/mol (NaBr2−, −458±2 kJ/mol (NaI2−, 24±5 kJ/mol (Na3Br2+, 143±5 kJ/mol (Na3I2+, −810±5 kJ/mol (Na2Br3−, and −675±5 kJ/mol (Na2I3−.

The Knudsen effusion mass spectrometric technique was used to study vapor species over praseodymium triiodide. The monomer, PrI 3 , and dimer, Pr 2 I 6 , molecules and the negative ions, PrI 4 − and Pr 2 I 7 − , were observed in saturated vapor in the temperature range from 856 K to 1048 K. The partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation obtained using the second and the third laws of thermodynamics (Δ s H °(298.15 K) = 291 ± 4 kJ mol −1 for PrI 3 , and Δ s H °(298.15 K) = 400 ± 30 kJ mol −1 for Pr 2 I 6 ). The equilibrium constants for various ion molecular reactions were measured and the enthalpies of reactions obtained. The enthalpies of formation, Δ f H °(298.15 K) kJ mol −1 , of gaseous molecules and ions were calculated and are as follows: −374 ± 6 (PrI 3 ), −929 ± 30 (Pr 2 I 6 ), −867 ± 30 (PrI 4 − ), −1432 ± 50 (Pr 2 I 7 − ).

The vaporization of the NaI-PrI3 quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI)n and (PrI3)n molecules (n = 1, 2) and Na+(NaI)n(n = 0–4) and I−(PrI3)n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI4, Na2PrI5, NaPrI3+, Na2PrI4+, Na3PrI5+, Na4PrI6+, NaPrI5−, and NaPr2I8−). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.

The molecular and ionic composition of vapor over holmium tribromide was studied by high-temperature mass spectrometry under the conditions of sublimation from a Knudsen effusion cell and from the open single crystal surface. The partial pressures of HoBr3 and Ho2Br6 in saturated vapor and the ratio between their sublimation coefficients under free vaporization conditions were determined. The intensities of lines in the electron impact mass spectra and their temperature dependences were different under Knudsen and Langmuir conditions, which was evidence of superthermal vibrational-rotational excitation of molecules sublimed from the open surface. The enthalpies and activation energies of sublimation of HoBr3 crystals as monomers and dimers were calculated. The emission of HoBr4− and Ho2Br7− negative ions was observed under both sublimation conditions. Ion-molecular equilibria in the LaBr3-HoBr3 system were studied. The enthalpies of formation of the HoBr3 and Ho2Br6 molecules and HoBr4− and Ho2Br7− negative ions in the gas phase were calculated.

The thermodynamic activities of sodium iodide and praseodymium triiodide in NaI-PrI3 binary system melts at 900 K were determined by high-temperature mass spectrometry. The activities were used to calculate the excess integral Gibbs energy of melt formation. A negative deviation of the system from the behavior of an ideal melt was observed.

The vaporization of praseodymium triiodide was studied by high-temperature mass spectrometry. Monomeric (PrI3) and dimeric (Pr2I6) molecules and the PrI 4 − and Pr2I 7 − negative ions were recorded in saturated vapor over the temperature range 842–1048 K. The partial pressures of neutral vapor components were determined. The enthalpies of sublimation Δs H o(298.15 K) in the form of monomers (291 ± 10 kJ/mol) and dimers (400 ± 30 kJ/mol) were calculated by the second and third laws of thermodynamics. The equilibrium constants of ion-molecular reactions were measured and the enthalpies of the reactions determined. The enthalpies of formation Δf H o(298.15 K) of molecules and ions in the gas phase were calculated (−373 ± 11, −929 ± 31, −865 ± 25, and −1433 ± 48 kJ/mol for PrI3, Pr2I6, PrI 4 − , and Pr2I 7 − , respectively).

The molecular and ionic vaporization of cerium tribromide from the effusion cell (Knudsen conditions) and the open surface of a CeBr3 single crystal (Langmuir conditions) were studied by high-temperature mass spectrometry. The CeBr3 and Ce2Br6 molecules and the CeBr4− and Ce2Br7− negative ions were observed as vapor constituents. The partial pressures of the molecules in saturated vapor and the ratio between the vaporization coefficients of monomers and dimers under free vaporization conditions were determined. The enthalpies and the activation energies of sublimation in the form of monomers and dimers were measured. Ion–molecular equilibria with the participation of negative ions were studied. The enthalpies of formation of molecules and ions in the gas phase were obtained.

The method of high-temperature mass spectrometry is used for studying the composition of saturated vapor over cerium and praseodymium tribromides. Monomer and dimer molecules are found in the temperature ranges of 789–994 K and 804–957 K for cerium and praseodymium, respectively. The partial pressures of vapor components are determined, p(Pa), the temperature dependences of which are approximated by the equations $$ \begin{gathered} \log p(CeBr_3 ) = ( - 14.63 \pm 0.08) \times 10^3 /T + (14.54 \pm 0.09), T = 789 - 994 K; \hfill \\ \log p(Ce_2 Br_6 ) = ( - 19.72 \pm 0.61) \times 10^3 /T + (17.60 \pm 0.64), T = 918 - 980 K; \hfill \\ \log p(PrBr_3 ) = ( - 14.13 \pm 0.12) \times 10^3 /T + (14.09 \pm 0.14), T = 804 - 957 K; \hfill \\ \log p(Pr_2 Br_6 ) = ( - 18.90 \pm 0.50) \times 10^3 /T + (17.15 \pm 0.53), T = 903 - 955 K. \hfill \\ \end{gathered} $$ The values of pressure of vapor components are used along with literature data for the calculation of enthalpies of sublimation in the form of monomer and dimer molecules by the procedures of the second and third laws of thermodynamics. Based on analysis of the results, thermodynamic parameters of monomer and dimer molecules (in kJ mol−1) are recommended, $$ \begin{gathered} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta _s H^0 (CeBr_3 , 298.15) = 305 \pm 5, \Delta _s H^0 (PrBr_3 , 298.15) = 293 \pm 5, \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta _s H^0 (Ce_2 Br_6 , 298.15) = 410 \pm 28, \Delta _s H^0 (Pr_2 Br_6 , 298.15) = 403 \pm 28, \hfill \\ \,\,\,\,\,\,\,\Delta _f H^0 (CeBr_3 , gas, 298.15) = - 587 \pm 6, \Delta _f H^0 (PrBr_3 , gas, 298.15) = - 597 \pm 7, \hfill \\ \Delta _f H^0 (Ce_2 Br_6 , gas, 298.15) = - 1372 \pm 28, \Delta _f H^0 (Pr_2 Br_6 , gas, 298.15) = - 1378 \pm 28. \hfill \\ \end{gathered} $$

A methodology based on measurements of ion-molecular equilibria using high-temperature mass spectrometry was proposed for determining the electronic work function ϕe of congruently subliming ionic crystals. Using the enthalpies of sublimation determined experimentally for the LnBr4− ion and LnBr3 molecule, the effective values of ϕe were for the first time obtained from the thermochemical cycles of LaBr3, CeBr3, ErBr3, HoBr3, and LuBr3 crystals. The resulting values were (±0.20 eV) 2.54, 3.35, 3.04, 2.85, and 3.05, respectively.

The geometric parameters, normal vibration frequencies, and thermochemical characteristics of the ions present in vapor over sodium fluoride, Na 2 F + , Na 3 , Na , and Na 2 , were calculated ab initio by the Hartree-Fock method and taking into account electron correlation. The main equilibrium configuration of all ions was found to be the linear configuration of D ∞ h symmetry. Pentaatomic ions could also exist as two iso- mers, planar cyclic of C 2 v symmetry and bipyramidal of D 3 h symmetry. Their energies were higher than that of the D ∞ h isomers, and their contents in vapor were negligibly low. The energies and enthalpies of dissociation of the ions with the elimination of the NaF molecule were calculated. The enthalpies of formation of the ions were obtained.

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na2Cl+, NaCl2−, Na3Cl2+, and Na2Cl3− ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na2Cl+ and NaCl2− triatomic ions have a linear equilibrium D∞h configuration. The pentaatomic ions can exist in the form of the D∞h linear isomer, C2v planar cyclic isomer, or D3h bipyramidal isomer. At ∼1000 K the Na3Cl2+ and Na2Cl3− ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions ΔfH0(0 K) was determined: 230 ± 2 kJ/mol (Na2Cl+), −96 ± 4 kJ/mol (Na2Cl3−), −616 ± 2 kJ/mol (NaCl2−), and −935 ± 4 kJ/mol (Na2Cl3−).

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.

The enthalpy stability of the LaCl4− and LuCl4− ions is assessed using high-temperature mass spectrometry. The enthalpy of Cl− detachment is determined to be ΔrH0(298.15 K) = 332 ± 10 kJ/mol for LaCl4− and 359 ± 10 kJ/mol for LuCl4−.

The dissociation energy of the intermetallic molecule AuMg was for the first time determined by the Knudsen-effusion mass spectrometry technique. Partial pressures of Au(g), Mg(g), AuMg(g) and Au2(g) species produced under equilibrium vaporization of an appropriate alloy were monitored in the temperature range 1870–2333 K. The collected data were analyzed by the second- and third-law methods for the gaseous equilibria AuMg(g) ¼ Au(g) + Mg(g) and AuMg(g) + Au(g) ¼ Au2(g) + Mg(g). The selected value for the dissociation energy of AuMg at 0 K is D � (AuMg) ¼

The experimentally measured values of the EuBr2 sublimation enthalpy and EuBr3– desorption enthalpy were used to construct a thermochemical cycle to determine the work function φe = 405 ± 39 kJ·mol–1 (4.2 ± 0.4 eV) for europium dibromide.

The thermal emission of positive and negative ions from crystalline SrCl2 in the temperature interval of 900–1100 K is studied by a mass spectrometric method under the conditions of both free-surface (FS) and Knudsen cell (KC) evaporation. In the case of FS measurements the (1 1 1) cleavage face is studied. The positive ions SrCl+, Sr+, Sr2Cl3+, and M+ (M: alkali) are identified in the emission fluxes in both kinds of experiments. Besides, in the FS measurements negative Cl− and SrCl3− ions are registered; the currents of negative ions are weaker than those of positive ones. While the emission currents show essentially exponential increases with temperature, they exhibit a number of anomalies around the temperature of the phase transition to the superionic state (Tc=1000 K). The results are analysed in the light of the terrace-ledge-kink and the surface charge models. It is concluded that the sign of surface charge of defect-related origin is negative for SrCl2, i.e., the Gibbs free energy for the formation of a chlorine vacancy is lower compared with that for an interstitial Cl−.

A new software StatThermo for calculation of thermodynamic functions using the molecular constants in Rigid Rotator – Harmonic Oscillator approximation has been developed. Program includes various prebuilt algorithms to calculate atom coordinates for the majority of simple compounds (with a number of atoms N ≤ 8). The developed software can make the calculation for two reference temperatures (0 or 298.15 K) and different pressures. One of the prominent features of StatThermo is taking into account the low-lying electronic levels. The software was tested on different organic and inorganic molecules and average errors was found as follows: 0.05 kJ∙mol–1 (H°(T)-H°(0)), 0.01 J∙mol–1∙K–1 (Ф°(T)), and 0.002 J∙mol–1∙K–1 (S°(T)). The program can also approximate by the polynomial the thermodynamic functions defined by user. A wide range of functional possibilities, flexible parameters of calculation, and feature of export results in the Visual Basic macro do the StatThermo powerful software for thermodynamic computations. StatThermo can connect to the MS Office and OpenOffice servers for the export of calculated data. The software can treat the Gaussian, Gamess, FireFly, Jaguar, MolPro, CFour, NWChem, ORCA, Priroda, PSI4, Q-Chem, and VASP output files. A multilingual and cross-platform support makes the StatThermo accessible for a lot of users. Forcitation:Dunaev A.M., KudinL.S. StatThermo® – new software for calculation of thermodynamic functions. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 40-46.

A mass spectrometric method is used to study positive and negative thermal ion emission from crystalline BaF 2 in the temperature interval of 1050–1400 K under the conditions of both free-surface (FS) and Knudsen cell (KC) evaporation. In the case of FS measurements the (1 1 1) cleavage face is studied. Positive ions BaF + , Ba + , BaCl + , Ba 2 F 3 + , and M + (M: alkali) are identified in emission fluxes in both kinds of experiments. Besides, in the FS measurements Ba 2 F 2 Cl + , Ba 2 FCl 2 + ions are registered. Weak currents of negative ions F − , Cl − , BaF 3 − , BaF 2 Cl − , BaFCl 2 − , and BaCl 3 − were detected above about 1300 K in the case of FS evaporation. In the KC case, negative ions were not observed up to 1400 K. The variation in thermal ion currents and their ratios with the temperature exhibits a number of anomalies around the temperatures of the phase transition to the superionic state ( T c =1299 K). The results are analysed in light of the terrace–ledge–kink and of the surface charge models.

The composition of saturated vapor over thulium trichloride is studied using the method of high-temperature mass spectrometry. Neutral (TmCl3) n and charged Cl–(TmCl3) n associates up to n= 5 and 8, respectively, have been registered for the first time in the temperature range from 868 to 1110 K. Partial pressures p(atm) of the vapor components are determined. The second and third laws of thermodynamics are used to calculate the sublimation enthalpies Δ s H° (298 K) in the form of monomeric and associated molecules, as well as the enthalpies of formation Δ f H° (298 K) of gaseous molecules and ions.

A Knudsen effusion cell mass spectrometric technique was used to study vapor species over CeCl(3) and SmCl(3). Monomer, dimer, and trimer (Sm(3)Cl(9)) molecules, and LnCl(4-), Ln(2)Cl(7-), Ln(3)Cl(10-) (Ln = Ce, Sm) negative ions, were observed in saturated vapor in the temperature range 958-1227 K. Partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation (Delta(s)H, 298 K, kJ.mol(-1)) to monomers and associated molecules obtained: 328 +/- 6 (CeCl(3)), 306 +/- 6 (SmCl(3)), 453 +/- 16 (Ce(2)Cl(6)), 408 +/- 12 (Sm(2)Cl(6)), and 468 +/- 40 (Sm(3)Cl(9)). Equilibrium constants for various chemical reactions were measured and the enthalpies of reactions obtained using the second and third laws of thermodynamics. The enthalpies of formation (Delta(f)H, 298 K, kJ.mol(-1)) of molecules and ions have been calculated as follows: -730 +/- 6 (CeCl(3)), -722 +/- 6 (SmCl(3)), -1663 +/- 16 (Ce(2)Cl(6)), -1649 +/- 13 (Sm(2)Cl(6)), -2617 +/- 40 (Sm(3)Cl(9)), -1250 +/- 15 (CeCl(4)(-)), -1252 +/- 15 (SmCl(4-)), -2184 +/- 35(Ce(2)Cl(7-)), -2172 +/- 26 (Sm(2)Cl(7-)), -3183 +/- 43 (Ce(3)Cl(10-)), and -3147 +/- 43 (Sm(3)Cl(10-)).