Journal of Spectroscopy
Volume 2016 (2016), Article ID 2368131, 9 pages
http://dx.doi.org/10.1155/2016/2368131

Research Article

Study of Molecular and Ionic Vapor Composition over CeI₃ by Knudsen Effusion Mass Spectrometry

A. M. Dunaev,¹ V. B. Motalov,¹ L. S. Kudin,¹ M. F. Butman,¹ and K. W. Krämer²

¹Research Institute of Thermodynamics and Kinetics, Ivanovo State University of Chemistry and Technology, Ivanovo 153000, Russia
²Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland

Received 7 August 2016; Accepted 17 October 2016

Academic Editor: Alessandro Longo

Copyright © 2016 A. M. Dunaev et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The molecular and ionic composition of vapor over cerium triiodide was studied by Knudsen effusion mass spectrometry. In the saturated vapor over CeI₃ the monomer, dimer, and trimer molecules and the negative ions I⁻, , and were identified in the temperature range of 753–994 K. The partial pressures of CeI₃, Ce₂I₆, and Ce₃I₉ were determined and the enthalpies of sublimation, (298.15 K) in kJ·mol⁻¹, in the form of monomers (), dimers (), and trimers () were obtained by the second and third laws of thermodynamics. The enthalpy of formation, (298.15 K) in kJ·mol⁻¹, of the CeI₃ (), Ce₂I₆ (), and Ce₃I₉ () molecules and the () and () ions were calculated. The electron work function, =  eV, for the CeI₃ crystal was evaluated.

1. Introduction

Vaporization thermodynamics of cerium triiodide is the focus of researcher’s attention so far. The first measurements of vapor pressure over CeI₃ were carried out by Knudsen effusion mass spectrometry (KEMS) [1] and Knudsen effusion Cahn microbalance [2] techniques. Further KEMS studies were performed by Chantry [3, 4], Struck and Feuersanger [5], and Ohnesorge [6]. In addition the vapor pressure of CeI₃ was determined by the torsion method [7], by optical absorption spectra [8], and recently by X-ray induced fluorescence [9]. In spite of the numerous experimental results [1–9], data on the vapor composition over CeI₃ are very scanty. Moreover, information on the ionic species in saturated vapor over CeI₃ is absent so far.

The present work continues our systematic investigations of the molecular and ionic sublimation of lanthanide halides by KEMS; see for example, [10–14]. The composition of the saturated vapor of CeI₃ was determined and the thermochemical data of the vapor constituents were refined on the basis of the latest sets of molecular parameters.

2. Experimental

A single-focusing magnetic sector type mass spectrometer MI1201 modified for high-temperature studies was used. The combined ion source allowed carrying out successive measurements in two modes; see Figure 1 (taken from [15]). In addition to a standard mode of electron ionization (EI) for analysis of neutral vapor species, a thermal ion emission (TE) mode was introduced for the analysis of charged vapor constituents formed inside an effusion cell as a result of thermal ionization. In the latter case, the ions are drawn out from the cell by a weak electric field (10⁴–10⁵ V/m) applied between the cell and the collimator (). The sample () was placed into a molybdenum cell () under dry conditions in a glove box and then transferred into the vaporization chamber of the mass spectrometer and evacuated. The lid of the cell had the cylindrical effusion orifice (Ø 0.3 × 0.8 mm). The vaporization-to-effusion area ratio was about 400. A resistance furnace was used for the heating of the cell. Its temperature was measured by a tungsten-rhenium thermocouple calibrated with silver to a ±5 K accuracy in the separate experiment.

Figure 1: Scheme of the mass spectrometer (taken from [15]). I—EI mode; II—TE mode. The details are given in text.

The vapor species effusing from the cell form a molecular beam, which reaches the ionization chamber () and intersects with an electron beam of specified energy. The ionization voltage is set by a computer using a programmable power supply AKIP-1125 in the range of 0–150 V with 10 mV resolution. The tungsten ribbon-type cathode () is directly heated by an controllable DC source. The current of the cathode was adjusted to provide a constant emission current of 0.25 A.

The ions formed by the collision of molecular species with electrons are extracted from the ionization chamber, focused, and accelerated by a system of electrostatic lenses (). The electrostatic capacitor mounted after the exit slit of the ion source allows us to study the distribution of ions by the vertical velocity component. The accelerating voltage (3 kV) is applied to the ionization chamber (IE mode) or to the effusion cell (TE mode). The polarity of the high voltage can be reversed with respect to the ground potential. Thus, both positive and negative ions can be analyzed. The ions are separated according to their mass-to-charge ratio in the magnetic field of an electromagnet () (90°, 200 mm curvature radius). The magnetic field strength is measured by a Hall probe. The ion current registration system (, ) includes a secondary electron multiplier Hamamatsu R595 () and a Picoammeter Keithley 6485 with 10 fA resolution and 20 fA typical noise. It allows measuring ion currents down to 10⁻¹⁸ A. The movable shutter () operated by a computer () allows distinguishing signals caused by the effusing species from those of the background. The special software “HTMSLab” was used to control experimental parameters, collect and process the data, and export the results into the database. Further details on the apparatus and experimental procedure can be found elsewhere [16–18].

The cerium triiodide sample was synthesized from cerium metal (99.9%, Metall Rare Earth Ltd.) and iodine (p.a., sublimed, Merck). The elements were sealed in an evacuated silica ampoule and slowly heated to 750°C until the reaction was completed. Afterwards the product was sublimed for purification in a sealed silica ampoule under vacuum at 750°C, that is, slightly below the melting point of CeI₃ at 766°C. The bright yellow CeI₃ is very hygroscopic. Its synthesis was performed under strictly oxygen-free and anhydrous conditions.

3. Results and Discussion

3.1. Neutral Vapor Species

In the IE mass spectra of the saturated vapor over cerium triiodide the Ce⁺(), CeI⁺(), (100), (31), (0.02), (0.01), (2.2), I⁺(22), and (0.02) ions, as well as the doubly charged Ce⁺⁺(0.5), CeI⁺⁺(), and () ions, were registered in the temperature range of 753–994 K. The relative ion currents are given in parentheses for the temperature of 990 K and the energy of ionizing electrons of 40 eV. The mass spectra were found to be constant over the whole evaporation time; see Figure 2.

Figure 2: Temperature dependence of the mass spectra of CeI₃. Heating and cooling runs are marked by solid and open symbols, respectively.

To determine the molecular precursors of the ions, the ionization efficiency curves (IEC) (Figure 3) and the temperature dependencies of ion currents (Figure 4) were analyzed. The ionizing electron energy in Figure 3 was corrected by the background signal of HI⁺ ( = 10.38 eV [19]). Appearance energies () were determined by vanishing current (VC) and linear extrapolation (LE) methods; average values are given in Table 1. The linear part for the LE method was determined as the segment between two points of inflection on the first-order derivative of the IEC inverse function [20]. The following conclusions were drawn: the ions containing one atom of cerium are formed as a result of direct () and dissociative (Ce⁺, CeI⁺, and ) ionization of the monomer CeI₃ molecules with negligibly small contributions from the fragmentation of more complex molecules; the , , and ions were produced by the dissociative ionization of the dimer Ce₂I₆ molecules; and the ion originated from the trimer molecule Ce₃I₉.

Table 1: Ion appearance energies (eV).

Reaction
Ion

This work
[1]
[3]
[5]
[30]

CeI₃ + ē = Ce⁺ + 3I + 2ē
Ce⁺

CeI₃ + ē = CeI⁺ + 2I + 2ē
CeI⁺

CeI₃ + ē = + I + 2ē

11.2

CeI₃ + ē = + 2ē

10.8
9.71

Ce₂I₆ + ē = + I + 2ē

Ce₃I₉ + ē = + I + 2ē

I + ē = I⁺ + 2ē
I⁺

~13.5
10.5

(a)

(b)

Figure 3: Ionization efficiency curves.

Figure 4: Temperature dependence of ion currents in the EI regime.

Along with the abovementioned ions I⁺ was also observed. The determined equal to  eV (Table 1) points out its origination from atomic iodine (ionization energy (I) = 10.4 eV [21]), which can be attributed to the partial decomposition of the sample with the formation of CeI₂. Nevertheless the reproducibility of the mass spectra in heating and cooling cycles (Figure 2), the shapes of IECs showing no brakes, and the determined values (Table 1) indicate unambiguously the absence of CeI₂ in the vapor. This fact agrees with the expected much lower volatility of CeI₂ compared to that of CeI₃ in the studied temperature range. Therefore it is assumed that the activity of CeI₃ in the solid state was unity.

The partial pressures of molecules () (see Table 2) were calculated according to the conventional KEMS procedure using the equation

where is the sensitivity constant of mass spectrometer (determined in a separate experiment with Ag; the vapor pressure of silver was taken from [22]), σ j is the ionization cross section of the jth molecule at the working energy of the ionizing electrons (calculated from the experimentally determined atomic cross sections, [23, 24], by the equation [25]), is the total ion current of the th ion species formed from the jth molecule, is the natural abundance of the measured isotope of the th ion, γ i is the ion-electron conversion coefficient of secondary electron multiplier for the th ion (−1/2 [26], where is the mass of ion), and is the temperature of the cell.

Table 2: Partial pressures (Pa) of the molecules.

CeI₃
Ce₂I₆
Ce₃I₉

T, K

T, K

T, K

885
54.5
878
3.59
916
0.85

872
47.8
915
26.8
957
7.45

877
55.4
957
182
932
1.83

877
54.7
933
57.0
907
0.41

914
235
906
14.3
905
0.65

957
1080
866
1.62
921
0.84

934
445
829
0.15
945
4.29

906
150
857
1.27
952
5.24

868
29.8
882
5.80
962
12.5

828
4.32
906
17.0
978
29.9

786
0.52
920
39.8
992
58.1

805
1.23
946
134
907
0.51

753
0.081
853
0.76
923
1.08

872
43.5
952
170
943
2.74

957
1210
963
323
969
15.3

857
20.3
978
566
994
54.2

882
59.5
992
1010

906
145
907
23.9

919
274
923
28.8

942
575
883
4.19

854
15.8
857
0.90

951
786
829
0.20

963
1280
811
0.035

979
1970
828
0.081

990
3020
857
0.64

908
150
884
3.77

923
244
917
24.0

883
40.1
943
105

856
15.5
969
343

829
4.06
994
999

811
1.48

826
3.24

856
13.7

883
48.8

918
189

944
551

969
1250

994
2880

The temperature dependence of the saturated vapor pressures of the monomer and oligomer molecules was approximated by the equation

The coefficients of equation (2) are given in Table 3.

Table 3: Coefficients of (2).

Species
T, K
A
B

CeI₃
753–994
33.35 ± 0.36
34.84 ± 0.41

Ce₂I₆
811–994
44.93 ± 0.62
43.10 ± 0.69

Ce₃I₉
905–994
49.62 ± 1.43
42.43 ± 1.52

The standard deviation is given with a “±” sign.

The partial pressures of the molecules of cerium triiodide from different references are compared in Figure 5. As one can see, all experimental vapor pressure values are scattered within about one order of magnitude. Temperature dependencies from the work of Hirayama et al. [2], Villani et al. [7], and Ohnesorge [6] lie below those obtained in this work. The fraction of the dimer molecules measured in this work and in [6] is about the same whereas the absolute pressures differ considerably. The vapor pressure of trimer molecules was determined in this study for the first time.

Figure 5: Temperature dependencies of the saturated vapor pressure: () p(CeI₃) from [9], () our data, () [2], () [7], and () [6]; (1′) p(Ce₂I₆) from [9], (2′) our data, and (5′) [6]; () p(Ce₃I₉) our data.

The enthalpies and entropies of sublimation of cerium triiodide in the form of monomer and oligomer molecules were determined from the temperature dependencies of the partial pressures of the saturated vapor species using the procedure for experimental data processing according to the second and third laws of thermodynamics; see Table 4. The thermodynamic functions required for calculations were taken from [22] for and evaluated in this work for the monomer and oligomer molecules in the state of an ideal gas (see Appendix).

Table 4: Enthalpies, (kJ·mol⁻¹), and entropies, (J·mol⁻¹·K⁻¹), of sublimation of cerium triiodide.

ΔT, K
T, K
N ¹
II law²
III law³
Ref.

(T)
(T)
(298)
(298)
(T)

=

753–994
893
38

This work

?
933
?

[1]

870–1015
945
32

[2]

810–953
877
50

[5]

854–1017
936
29

[6]

910–1031
970
81

[7]

1000
1

[8]

1072–1136
1094
5

[8]

1080–1400
1250
?

[9]

297

[22]

322

[27]

280

[28]

[29]

(298.15 K) =

=

811–994
893
30

This work

825–953
898
50

[5]

854–1017
936
17

[6]

1080–1400
1250
?

[9]

(298.15 K) =

=

907–994
949
16

This work

(298.15 K) =

¹Number of measurements.

²The original errors are given for the literature data, the standard deviations for this work.

³The uncertainties are mainly determined by those in thermodynamic functions.

⁴The uncertainty of the recommended values was calculated by Student’s method (monomer) and accepted as the third law ones (others).

As it is seen from Table 4, the values of (298.15) and (T) obtained in this work by the second and third laws are in a fair agreement for both monomer and oligomer molecules. The same can be said about the results for the monomer molecules from [2, 7]. The data of the work [9] are in notably worse agreement, whereas those of [6, 8] do not agree within the given uncertainties. At the same time, the third law values for all the data are in a good consent with each other. The temperature trend of the third law values (298.15) is given in Figure 6, from which one can see that the data of this work and [2, 9] do not show a pronounced temperature dependence as compared to those of [6, 7]. Taking into account this analysis, the recommended values were selected and emphasized in bold in Table 4. The early estimates [27, 28] made for monomers differ considerably from the recommended value, while the assessments given in [22, 29] agree with the experimental data.

Figure 6: Temperature dependencies of the third law (298.15 K) values: () monomer from [9], () our data, () [2], () [7], and () [6]; (1′) dimer from [9], (2′) our data, and (5′) [6]; () trimer our data.

The standard formation enthalpies, (298.15 K), are equal to  kJ·mol⁻¹ (CeI₃),  kJ·mol⁻¹ (Ce₂I₆), and  kJ·mol⁻¹ (Ce₃I₉) and were calculated from the recommended H°(298.15 K) values. The formation enthalpy of crystalline cerium triiodide, (; 298.15 K) = −669 kJ·mol⁻¹ [22], was used.

3.2. Charged Vapor Species

In the TE mass spectra in the temperature range of 747–960 K the I⁻(0.44), (0.18), (100), and (0.08) ions were identified with the relative ion currents given in parentheses for T = 846 K.

Additional experiments with the CeI₃-PrI₃ binary system were performed to determine the enthalpy of formation of ions. The enthalpy of exchange ion-molecular reaction (5) was found to be  kJ·mol⁻¹. The enthalpy of formation of (298.15 K) =  kJ·mol⁻¹ was used as reference value. It was obtained by recalculation of the data ( kJ·mol⁻¹) [13] with the thermodynamic function used in this work. The experimental equilibrium constants of reaction (3) and reaction (4) investigated over pure CeI₃ are listed in Table 5:

Table 5: Experimental data for reactions (3) and (4).

Reaction (3)
Reaction (4)

T (K)

T (K)

889
0.35
868
6.39

865
0.39
862
6.61

835
0.30
898
5.92

846
0.49
932
5.43

907
0.41
960
4.94

934
0.39
924
5.49

966
0.38
892
5.94

956
0.37
846
6.67

929
0.34

906
0.22

856
0.34

806
0.38

854
0.30

884
0.38

902
0.30

950
0.40

976
0.30

The reaction enthalpies were calculated by the second and third laws of thermodynamics; see Table 6. The evaluation of the thermodynamic functions of the and ions is described in Appendix.

Table 6: Enthalpies (kJ·mol⁻¹) of reactions (3) and (4).

ΔT, K
T, K
N ¹
II law²
III law³
Ref.

(T)
(298.15 K)
(298.15 K)

+ = +

806–976
897
17

This work

= +

842–960
896
12

This work

¹Number of measurements.

²The original errors are given for the literature data, the standard deviations for this work.

³The uncertainties are mainly determined by those in thermodynamic functions.

One can see that the agreement for the enthalpy of reaction (3) obtained by the second and third laws is good. (, 298.15 K) =  kJ·mol⁻¹ was recommended. This value is in agreement with those  kJ·mol⁻¹ obtained by Chantry from the enthalpy of the reaction = + and recalculated with our sublimation enthalpy and thermodynamic functions. The selected formation enthalpy of the ion is  kJ·mol⁻¹ (third law) and was obtained for the first time.

3.3. Thermodynamic Properties Derived from IECs

The enthalpies of ion-molecular reactions were calculated from the differences of the measured values given in Table 1; see Table 7. On their basis the standard formation enthalpies of the ions were determined; see Table 8. The accurate values of (Ce⁺, 298.15 K) =  kJ·mol⁻¹ [22] and (I, 298.15 K) =  kJ·mol⁻¹ [22] and the formation enthalpies of the CeI₃, Ce₂I₆, and Ce₃I₉ molecules obtained in this work (see above) were used as references. The comparison of our results with the data obtained by photoelectron spectroscopy [30], computation [31], and assessment [32] shows that all data are in agreement within the given errors; see Table 8.

Table 7: Ion-molecular reactions (kJ·mol⁻¹).

Reaction
This work
[1]
[3]
[5]
[30]
[31]

=

393

=

=

39

+ = + 2

+ = + 2

Table 8: Ion formation enthalpies (kJ·mol⁻¹).

Ion
This work
[1]
[3]
[32]
[31]

CeI⁺

717
760
671

476

535

Analysis of the ion-molecular reaction enthalpies confirmed the weakness of the first cerium iodine bond in comparison with the other two. Probably, it explains the lower enthalpy of the formation of ( kJ·mol⁻¹) compared to ( kJ·mol⁻¹).

The formation enthalpy of gaseous CeI₃ ( kJ·mol⁻¹) obtained from the vapor pressure measurement is in a good agreement with those calculated from the appearance energies ( kJ·mol⁻¹) and with the value (−381 kJ·mol⁻¹) assessed by Sapegin et al. [33] (Table 9). The coincidence of the formation enthalpy values of , as determined from the thermodynamic and threshold approaches, points out a negligible contribution from the excitation and kinetic energy of the fragments. The atomization energy derived from (CeI₃, 298.15 K) =  kJ·mol⁻¹ was found to be  kJ·mol⁻¹. It yields the average bond strength equal to  kJ·mol⁻¹.

Table 9: Formation enthalpies of (kJ·mol⁻¹).

This work
from IEC
This work
from
[1]
[9]
[33]

>−376 ± 50
−371 ± 9
−436 ± 50
−349
−381

3.4. Electron Work Function

The mass spectrometric approach for the work function determination is based on the use of thermochemical cycles including desorption enthalpies of ions and sublimation enthalpies of molecules as described elsewhere [34]. The desorption enthalpy of the ions, (851 K) =  kJ·mol⁻¹, and the ions, (902 K) =  kJ·mol⁻¹, were obtained from the temperature dependence of their ion currents; see Figure 7. The electron work function was calculated in accordance with the following expressions:

where EA(I) is the electron affinity of iodine [22], D(CeI₃) is the dissociation enthalpy of the CeI₃ molecule, H°() is the enthalpy of the = I⁻ + CeI₃ reaction (Table 6), and H°() is the enthalpy of the = I⁻ + 2CeI₃ reaction.

Figure 7: Temperature dependencies of and ion currents.

The values equal to  eV and  eV were obtained from (5) and (6), respectively. They turned out to be close to (LaI₃) =  eV [14].

4. Conclusions

New experimental data on the saturated vapor composition of CeI₃ have been obtained by a Knudsen effusion mass spectrometer. The monomer, CeI₃, dimer, Ce₂I₆, and trimer, Ce₃I₉, molecules, as well as the [I(CeI₃)n]⁻ ions (0–2), have been observed in the temperature range of 747–994 K. The Ce₃I₉ molecules and the ions were detected for the first time. The sublimation enthalpies of the monomer and oligomer molecules were calculated by the second and third laws of thermodynamics. Critical analysis of all available data allowed us to recommend the following enthalpies of sublimation: (298.15 K) in kJ·mol⁻¹: (monomer), (dimer), and (trimer) and to calculate the formation enthalpies, (298.15 K) in kJ·mol⁻¹: (CeI₃), (Ce₂I₆), (Ce₃I₉), (), and (). The electron work function for cerium triiodide ( eV) has also been evaluated.

Appendix

A. Description of the Used Thermodynamic Functions of Molecules and Ions

A.1.

The thermodynamic functions of CeI₃ in the solid and liquid state were taken from [22].

A.2.

For the first time the thermodynamic functions of monomer molecules CeI₃ in the state of an ideal gas were evaluated by Myers and Graves [35] in the rigid rotator-harmonic oscillator (RRHO) approximation; these were included in the handbooks by Pankratz [36] and Barin [37]. Later the assessment of the functions was made by Osina et al. [38]; they can be found in the IVTANTHERMO database [22]. Recently Solomonik et al. [39] performed quantum-chemical calculations for at a multireference configuration interaction MRCISD+Q level of theory taking into account relativistic effects; a significant spin-orbit coupling effect on the molecular properties was revealed.

The data used in this work are based on those from [22] taking into account the low lying electronic states computed in [39].

A.3.

The thermodynamic functions of dimer molecules were calculated in the RRHO approximation using the molecular constants (symmetry ) from [40]. The electronic contribution was taken as doubled compared with the monomers in accordance with [41].

A.4.

The thermodynamic functions of trimers were assessed by the additive approach with an empiric correction based on the functions of the monomer and oligomer molecules of LuCl₃ [42] using the following expressions:

where TDF means the thermodynamic functions Ф°(T) or H°(T) − H°(0).

A.5.

The thermodynamic functions of the ions were computed in the RRHO approximation assuming a coincidence of the functions for and CeI₄ based on the molecular constants taken from [43] and the electronic states from [39].

A.6.

The thermodynamic functions of ions were evaluated by a comparative method on the basis of those for LnI₃, (Ln = La, Ce) [22, 44], Ce₂I₆ [40], and [14] using the following relation:

where

The thermodynamic functions used in this work were approximated by the polynomial

The coefficients of (A.4) are listed in Table 10.

Table 10: Coefficients of polynomial (A.4).

–c

0–1033
47.08
2.326
3.838
2.391
8.699
1.760

1033–1500
106.9
26.03
16.90
1.830
3.165
0.289

CeI₃
0–1500
110.0
1.489
4.011
3.480
12.77
2.158

0–1500
122.9
1.780
4.748
4.156
15.36
2.604

Ce₂I₆
0–1500
177.9
2.760
7.349
6.477
23.88
4.043

0–1500
27.52
16.59
20.47
4.390
9.010
0.966

Ce₃I₉
800–1500
992.1
441.8
194.6
2.251
1.601
1.060

The errors in the functions of Gibbs energy estimated in this work are assumed to be equal to ±5 (CeI₃), ±25 (Ce₂I₆), ±40 (), and ±50 (Ce₃I₉) J mol⁻¹ K⁻¹.

Competing Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

This work was supported by the Ministry of Education and Science of the Russian Federation (Project no. 4.1385.2014 K).

References

C. Hirayama and P. M. Castle, “Mass spectra of rare earth triiodides,” Journal of Physical Chemistry, vol. 77, no. 26, pp. 3110–3114, 1973.

C. Hirayama, J. F. Rome, and F. E. Camp, “Vapor pressures and thermodynamic properties of lanthanide triiodides,” Journal of Chemical & Engineering Data, vol. 20, no. 1, pp. 1–6, 1975.

P. J. Chantry, “Positive ion appearance potentials measured in CeI₃,” The Journal of Chemical Physics, vol. 65, no. 11, pp. 4421–4425, 1976.

P. J. Chantry, “Negative ion formation in cerium triiodide,” The Journal of Chemical Physics, vol. 65, no. 11, pp. 4412–4420, 1976.

C. W. Struck and A. E. Feuersanger, “Knudsen cell measurements of CeI₃(s) sublimation enthalpy,” High Temperature Science, vol. 31, pp. 127–145, 1991.

M. Ohnesorge, Untersuchungen zur Hochtemperaturchemie quecksilberfreier Metallhalogenid-Entladungslampen mit keramischem Brenner [Ph.D. thesis], Forschungszentrum Jülich, Jülich, Germany, 2005.

A. R. Villani, B. Brunetti, and V. Piacente, “Vapor pressure and enthalpies of vaporization of cerium trichloride, tribromide, and triiodide,” Journal of Chemical and Engineering Data, vol. 45, no. 5, pp. 823–828, 2000.

C. S. Liu and R. J. Zoilweg, “Complex molecules in cesium-rare earth iodide vapors,” The Journal of Chemical Physics, vol. 60, pp. 2400–2413, 1970.

J. J. Curry, E. G. Estupiñán, W. P. Lapatovich et al., “Study of CeI₃ evaporation in the presence of group 13 metal-iodides,” Journal of Applied Physics, vol. 115, no. 3, Article ID 034509, 2014.

D. N. Sergeev, M. F. Butman, V. B. Motalov, L. S. Kudin, and K. W. Krämer, “Knudsen effusion mass spectrometric determination of the complex vapor composition of samarium, europium, and ytterbium bromides,” Rapid Communications in Mass Spectrometry, vol. 27, no. 15, pp. 1715–1722, 2013.

D. N. Sergeev, A. M. Dunaev, M. F. Butman, D. A. Ivanov, L. S. Kudin, and K. W. Krämer, “Energy characteristics of molecules and ions of ytterbium iodides,” International Journal of Mass Spectrometry, vol. 374, pp. 1–3, 2014.

L. S. Kudin, D. E. Vorob'ev, and A. E. Grishin, “The thermochemical characteristics of the LnCl₄⁻ and Ln₂Cl₇⁻ negative ions,” Russian Journal of Physical Chemistry A, vol. 81, no. 2, pp. 147–158, 2007.

V. B. Motalov, D. E. Vorobiev, L. S. Kudin, and T. Markus, “Mass spectrometric investigation of neutral and charged constituents in saturated vapor over PrI₃,” Journal of Alloys and Compounds, vol. 473, no. 1-2, pp. 36–42, 2009.

A. M. Dunaev, L. S. Kudin, V. B. Motalov, D. A. Ivanov, M. F. Butman, and K. W. Krämer, “Mass spectrometric study of molecular and ionic sublimation of lanthanum triiodide,” Thermochimica Acta, vol. 622, pp. 82–87, 2015.

D. N. Sergeev, Energy characteristics of molecules and ions of lanthanide bromide (Sm, Eu, Yb) studied by high temperature mass spectrometry [Ph.D. thesis], 2011.

A. M. Dunaev, A. S. Kryuchkov, L. S. Kudin, and M. F. Butman, “Automatic complex for high temperature investigation on basis of mass spectrometer MI1201,” Izvestiya Vysshikh Uchebnykh Zavedeniy Seriya “Khimiya I Khimicheskaya Tekhnologiya”, vol. 54, pp. 73–77, 2011 (Russian).

D. N. Sergeev, A. M. Dunaev, D. A. Ivanov, Y. A. Golovkina, and G. I. Gusev, “Automatization of mass spectrometer for the obtaining of ionization efficiency functions,” Pribory i Tekhnika Eksperimenta, vol. 1, pp. 139–140, 2014 (Russian).

A. M. Dunaev, V. B. Motalov, and L. S. Kudin, “High temperature mass spectrometric method for the determination of work function of the ionic crystals: triiodide of lanthanum, cerium, and praseodymium,” Russian Chemical Journal, vol. 59, pp. 85–92, 2015.

K. Kimura, S. Katsumata, Y. Achiba, T. Yamazaki, and S. Iwata, “Ionization energies, Ab initio assignments, and valence electronic structure for 200 molecules,” in Handbook of HeI Photoelectron Spectra of Fundamental Organic Compounds, p. 268, Japan Scientific Societies Press, Tokyo, Japan, 1981.

D. N. Sergeev, M. F. Butman, V. B. Motalov, L. S. Kudin, and K. W. Krämer, “Extrapolated difference technique for the determination of atomization energies of Sm, Eu, and Yb bromides,” International Journal of Mass Spectrometry, vol. 348, pp. 23–28, 2013.

D. R. Lide, Ed., CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, Fla, USA, 90th edition, 2009.

L. V. Gurvich, V. S. Iorish, I. V. Veitz et al., Eds., A Thermodynamic Database of Individual Substances and Software System for the Personal Computer, IVTANTERMO for Windows, Glushko Thermocenter of RAS, Version 3.0, 2000.

S. Yagi and T. Nagata, “Absolute total and partial cross sections for ionization of free lanthanide atoms by electron impact,” Journal of the Physical Society of Japan, vol. 70, no. 9, pp. 2559–2567, 2001.

T. R. Hayes, R. C. Wetzel, and R. S. Freund, “Absolute electron-impact-ionization cross-section measurements of the halogen atoms,” Physical Review A, vol. 35, no. 2, pp. 578–584, 1987.

K. Hilpert, “High temperature mass spectrometry in materials research,” Rapid Communications in Mass Spectrometry, vol. 5, no. 4, pp. 175–187, 1991.

J. Drowart, C. Chatillon, J. Hastie, and D. Bonnell, “High-temperature mass spectrometry: instrumental techniques, ionization cross-sections, pressure measurements, and thermodynamic data (IUPAC Technical Report),” Pure and Applied Chemistry, vol. 77, no. 4, pp. 683–737, 2005.

R. C. Feber, Heats of Dissociation of Gaseous Halides. TID-4500, Los Alamos Scientific Laboratory, 40th edition, 1965.

C. W. Struck and J. A. Baglio, “Estimates for the enthalpies of formation of rare-earth solid and gaseous trihalides,” High Temperature Science, vol. 31, pp. 209–237, 1992.

R. J. M. Konings and A. Kovács, “Thermodynamic properties of the lanthanide (III) halides,” in Handbook on the Physics and Chemistry of Rare Earths, K. Gschneidner Jr., J.-C. G. Bünzli, and V. Pecharsky, Eds., vol. 33, pp. 147–247, Elsevier Science B.V., 2003.

B. Ruščić, G. L. Goodman, and J. Berkowitz, “Photoelectron spectra of the lanthanide trihalides and their interpretation,” The Journal of Chemical Physics, vol. 78, no. 9, pp. 5443–5467, 1983.

L. A. Kaledin, M. C. Heaven, and R. W. Field, “Thermochemical properties (D°₀ and IP) of the lanthanide monohalides,” Journal of Molecular Spectroscopy, vol. 193, no. 2, pp. 285–292, 1999.

S. A. Mucklejohn, “Molecular constants and standard enthalpies of formation for the lanthanide monohalide gaseous cations, LnX⁺, X = F, Cl, Br, I,” Journal of Light and Visual Environment, vol. 37, no. 2-3, pp. 78–88, 2013.

A. M. Sapegin, A. V. Baluev, and O. P. Charkin, “Formation enthalpies and atomization energies of gaseous lanthanide halides,” Russian Journal of Inorganic Chemistry, vol. 32, pp. 318–321, 1987 (Russian).

L. S. Kudin, M. F. Butman, D. N. Sergeev, V. B. Motalov, and K. W. Krämer, “Determination of the work function for europium dibromide by knudsen effusion mass spectrometry,” Journal of Chemical & Engineering Data, vol. 57, no. 2, pp. 436–438, 2012.

C. E. Myers and D. T. Graves, “Thermodynamic properties of lanthanide trihalide molecules,” Journal of Chemical and Engineering Data, vol. 22, no. 4, pp. 436–439, 1977.

L. B. Pankratz, “Thermodynamic properties of halides,” United States Bureau of Mines, Bulletin 674, 1984

I. Barin, Thermochemical Data of Pure Substances, John Wiley & Sons, 3rd edition, 1995–1999.

E. L. Osina, V. S. Yungman, and L. N. Gorokhov, “Thermodynamic properties of lanthanide triiodide molecules,” Issledovano v Rossii, vol. 1–4, pp. 124–132, 2000 (Russian).

V. G. Solomonik, A. N. Smirnov, O. A. Vasiliev, E. V. Starostin, and I. S. Navarkin, “Nonemprirical study on the electronic structure of cerium, praseodymium, and ytterbium trihalide molecules,” Izvestiya Vysshikh Uchebnykh Zavedeniy Seriya “Khimiya I Khimicheskaya Tekhnologiya”, vol. 57, pp. 26–27, 2014 (Russian).

A. Kovács, “Molecular vibrations of rare earth trihalide dimers M2X6 (M=Ce, Dy; X=Br, I),” Journal of Molecular Structure, vol. 482-483, pp. 403–407, 1999.

L. N. Gorokhov, G. A. Bergman, E. L. Osina, and V. S. Yungman, “High temperature materials chemistry,” in Proceedings of the 10th International IUPAC Conference, K. Hilpert, F. W. Froben, and L. Singheiser, Eds., pp. 103–106, Forschungszentrum Juelich, Germany, April 2000.

A. M. Pogrebnoi, L. S. Kudin, A. Yu. Kuznetsov, and M. F. Butman, “Molecular and ionic clusters in saturated vapor over lutetium trichloride,” Rapid Communications in Mass Spectrometry, vol. 11, no. 14, pp. 1536–1546, 1997.

V. G. Solomonik, A. Y. Yachmenev, and A. N. Smirnov, “Structure, force fields, and vibrational spectra of cerium tetrahalides,” Journal of Structural Chemistry, vol. 49, no. 4, pp. 613–620, 2008.

V. G. Solomonik, A. N. Smirnov, and M. A. Mileyev, “Structure, vibrational spectra, and energetic stability of LnX₄⁻ ions (Ln=La, Lu; X=F, Cl, Br, I),” Russian Journal of Coordination Chemistry, vol. 31, no. 3, pp. 203–212, 2005.