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  • 1
    Electronic Resource
    Electronic Resource
    Thermochemistry of the gaseous osmium oxides (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 2325-2328 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100184a057
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  • 2
    Electronic Resource
    Electronic Resource
    The entropies and probable symmetries of the gaseous thorium and uranium tetrahalides (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8270-8275 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460111
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  • 3
    Electronic Resource
    Electronic Resource
    Thermochemistry of the gaseous thorium bromides (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5983-5989 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459483
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  • 4
    Electronic Resource
    Electronic Resource
    High-temperature equilibrium studies of the gaseous thorium chlorides (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6124-6130 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458335
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  • 5
    Electronic Resource
    Electronic Resource
    Sublimation studies of NpO2F2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2417-2421 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463080
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  • 6
    Electronic Resource
    Electronic Resource
    Redetermination of the thermochemistry of gaseous UF5, UF2, and UF (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1420-1425 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460000
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  • 7
    Electronic Resource
    Electronic Resource
    Dissociation energies of BaI and CaI from equilibrium studies (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3830-3833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Effusion-beam mass spectrometry was used to study the gaseous dissociation equilibrium BaI=Ba+I and the isomolecular exchange reactions of BaI and CaI with ScI over wide temperature ranges, and thermochemical data were derived from second law analysis. The results yielded the dissociation energies D(open circle)0(BaI) =76.2±1.5 kcal mol−1 and D(open circle)0(CaI) =67.0±2 kcal mol−1. Both of these values are about 5 kcal mol−1 larger than previous results obtained in this laboratory from third law analysis of other reactions. Reasons for the disparities are discussed. Our new second result for BaI is in good agreement with a recent value obtained from crossed molecular beam studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461888
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  • 8
    Electronic Resource
    Electronic Resource
    Sublimation studies of NpF4 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1950-1953 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The sublimation reaction NpF4(s) = NpF4(g) was measured over the range 820–980 K using Knudsen effusion mass spectrometry. The ionization potential of NpF4(g) is 10.4 +/−0.3 eV. The enthalpy of sublimation from second law analysis is 288.1+/−10.0 kJ mol−1, while the second law entropy of sublimation is 199.1+/−11.0 J K−1 mol−1, both at 298 K. The calculated enthalpy of formation of NpF4(g) is −1585.9+/−17.0 kJ mol−1 and the entropy is 351.8+/−12.0 J K−1 mol−1 at 298 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463131
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  • 9
    Electronic Resource
    Electronic Resource
    Mass spectrum and sublimation pressure of sodium oxide vapor: Stability of the superoxide molecule NaO2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4076-4081 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The total sublimation pressure of Na2O(c) has been measured in the range 1000–1050 K by the torsion-effusion method, and the mass spectra of vapors over Na2O(c) and Na2O2(c) have been examined in order to resolve several issues regarding the thermochemical stability of the superoxide molecule NaO2. Measured torsion-effusion pressures are completely consistent with the primary sublimation process Na2O(c)=2Na(g)+0.5 O2(g) and set an upper limit of 200 kJ mol−1 for the bond strength D0(Na–O2). The ionization efficiency curves of Na+ and O2+ in the mass spectrum of vapor over Na2O(c) show no evidence for fragmentation contributions from NaO2. In addition, the absence of a detectable Na+/NaO2 fragment ion signal in vapor over Na2O2(c) can be used to derive an even tighter upper bound of 180 kJ mol−1 for D0(Na–O2). These results are in conflict with various kinetic analyses yielding D0(Na–O2) values of 202 to 243 kJ mol−1, but are in accord with rigorous theoretical calculations giving values near 160 kJ mol−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465043
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrahigh-efficiency optical modulation ((approximately-greater-than)20 W/A) by interferometric frequency→intensity conversion of gain-levered semiconductor lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1715-1717 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is theoretically and experimentally demonstrated that a peculiar amplitude/phase coupling characteristic between the modulated and noise output of gain-levered lasers leads to a simultaneous increase in the modulation efficiency and a reduction in the intensity noise by interferometric frequency→intensity conversion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105118
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