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  • 11
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 5316-5319 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 2325-2328 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8270-8275 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The sublimation entropies of the thorium and uranium tetrahalides (except UI4 ) have been evaluated from torsion–effusion vapor pressure measurements and the results have been analyzed for compatibility with the spectroscopic and molecular constants of the gaseous molecules. New effusion pressure measurements are reported here for UCl4, UBr4, and ThI4. For UF4, UCl4, and ThF4, where thermal data are available for the solid phases, the experimental entropies of gaseous UF4 and UCl4 are incompatible with regular tetrahedral symmetries, while that of ThF4 is in close accord with a Td structure. A comparison of the entropies of sublimation shows that ThCl4 most likely has Td symmetry, while UBr4, ThBr4, and ThI4 probably do not; less-reliable total entropy data for the species are in full accord with these conclusions. The results are discussed in terms of structural information in the literature.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5983-5989 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The sublimation of ThBr4(s) was studied by the torsion-effusion and mass spectrometric methods in the range 600–750 K; only monomeric ThBr4 vapor was observed, and the pertinent thermodynamic parameters were derived. The gaseous lower-valent species ThBr3, ThBr2, and ThBr were identified in the bromination of Th(s) at 1500 to 2000 K, and several reaction equilibria involving these species were studied by mass spectrometry over wide temperature ranges for second law analysis. Reaction enthalpies, bond dissociation energies, and standard enthalpies of formation were derived from the results. Unlike ThF4 and ThCl4, the sublimation entropy indicates that ThBr4 may have a distorted tetrahedral structure. Bond dissociation energies and related thermodynamic properties are discussed and compared with values in other thorium and uranium halides.
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  • 15
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6124-6130 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-temperature gaseous equilibria among the species Th, ThCl, ThCl2, and ThCl3 were studied by mass spectrometry over broad temperature ranges; both enthalpy and entropy data were derived by the second law procedure. In addition, the sublimation of ThCl4 was studied by the torsion-effusion method and the thermodynamics of the gaseous tetrachloride were evaluated. Individual bond dissociation energies in ThCl4 fall within the range 489–545 kJ mol−1, and vary with ligand number in a way similar to ThF4. Only ThCl appears to have a significant electronic entropy in the experimental temperature range. For ThCl4 the experimental entropy indicates the likelihood of a regular tetrahedral structure as with ThF4, but unlike the uranium tetrahalides which appear to be distorted tetrahedra. In the mass spectrum of ThCl4, the fragment ions ThCl+3, ThCl+2, and ThCl+ show a larger and more nearly correct temperature dependence than the parent ion ThCl+4. Results are compared with those of other thorium and uranium halides.
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  • 16
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4909-4911 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation equilibrium AlBr=Al+Br was studied by effusion beam mass spectrometry over the range 1970 to 2260 K and the dissociation energy D00(AlBr) was derived as 4.41±0.06 eV. This value is in general agreement with other fragmentary thermochemical results, but it is lower than a value derived from a short extrapolation of vibrational levels in the excited 1π state, doubtless because of a potential maximum of about 0.22 eV in that state. A Birge–Sponer extrapolation of the ground state vibrational levels, when corrected for degree of ionicity, yields a D00 value in close accord with the experimental result, but an electrostatic model calculation falls short by 0.45 eV.
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5825-5828 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mass spectrometry was used to identify and to thermochemically characterize the gaseous fluorides RuF4 , RuF3 , RuF2 , and RuF generated by fluorination of Ru powder in a platinum effusion cell. Reaction enthalpies and bond dissociation energies were derived from equilibrium measurements involving these species, yielding the following results in kJ mol−1 : D°(F3 Ru–F)=361; D°(F2 Ru–F)=339; D°(FRu–F)=464; and D°(Ru–F)=402. The results show that the +4 oxidation state dominates the high temperature chemistry of the Ru–F system. Results are compared with the properties of the neighboring Mo–F system.
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2417-2421 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using Knudsen effusion mass spectrometry, we have identified the following reaction as the sublimation decomposition mechanism of NpO2F2(s): 2NpO2F2(s)=NpO2(s)+O2(g)+NpF4(g). From second-law analysis of the measured pressures of NpF4(g) over the temperature range 820–985 K the derived enthalpy change at 298 K is 556.8±12.2 kJ/mol and the entropy change is 342.4 ±13.8 J/K mol. From these values and enthalpies of formation and entropies reported in the literature for the other species we calculate the enthalpy of formation of NpO2F2(s) to be −1608±10 kJ/mol and the entropy to be 147±9 J/K mol.
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1420-1425 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Because of new studies questioning an earlier determination of the thermochemistry of UF5(g), we have reexamined the gaseous equilibrium Ag+UF5=AgF+UF4 by mass spectrometry over a broader temperature range, and have obtained more definitive results, leading to Δf H0298 (UF5,g)=−1929±10 kJ mol−1. Included was an independent thermochemical study of AgF which yielded Δf H0298 (AgF,g)=7.5±6 kJ mol−1 and D00 (AgF)=3.66±0.06 eV. Additionally, second-law measurements of the gaseous reaction U+UF2=2UF corroborated earlier results showing that D(U–F)〉D(FU–F), while the reverse holds in the U–Cl and U–Br systems. A revised set of bond dissociation energies and enthalpies of formation for the gaseous UFn species is presented, consistent with all key thermochemical values. This new information is discussed in terms of other results in the literature.
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  • 20
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1158-1164 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gaseous species ThF, ThF2, ThF3, and ThF4 were generated in a heated effusion beam source, and were identified and characterized by mass spectrometry. An oxygen impurity in the sample also led to the characterization of the gaseous oxyfluoride ThOF. Reaction equilibria involving these species were studied over large temperature ranges, leading to the derivation of both enthalpy and entropy data for these species. The vapor pressure and vaporization thermodynamics of ThF4(s) were also determined. Derived bond dissociation energies in ThF4 oscillate about a mean value of 670±25 kJ mol−1, with a distinct pattern similar to other metal tetrafluorides. Absolute entropies calculated from the equilibrium data indicate moderate electronic level contributions for the odd-electron molecules ThF and ThF3, but not for the even-electron species ThF2 and ThF4. Furthermore, the experimental entropy of ThF4 is compatible with a regular tetrahedral configuration, rather than the distorted configuration of lower symmetry found earlier for UF4 and UCl4. Thermochemical properties of the Th–F species are presented and the comparison with the corresponding uranium fluorides is discussed.
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