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The gaseous equilibria in the Dy-Br and Dy-I systems are examined with the help of effusion-beam mass spectrometry. The derivation of individual bond disassociation energies (BDE) in the species is discussed.

The molecule BCl was generated by chlorination of B(s) with both MgCl2 and SrCl2 in a heated effusive beam source, and identified by mass spectrometry. Gaseous equilibria in the B–Mg–Cl and B–Sr–Cl systems were studied in the regions 1350–1600 K and 1760–1830 K, respectively, and the dissociation energy D0°(BCl)=121.3±1.1 kcal mol-1 (5.26±0.05 eV) was derived from thermochemical analysis. When compared with a dissociation limit derived from a short upper state extrapolation, this result indicates a potential hump of about 6 kcal mol-1 in the A 1Π state of BCl. Electron impact measurements yielded an ionization potential of 10.03±0.10 eV for BCl, which can be used to evaluate D0°(BCl+)=81.4±2.6 kcal mol-1 (3.53±0.11 eV). Other values in the literature, some of which differ considerably from the new results, are discussed. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The gaseous equilibria MCl+Ag=M+AgCl and M+MCl2=2 MCl, where M=Cr, Mn, Fe, Co, and Ni were studied by mass spectrometry in the region around 1500 K, and thermochemical data were derived by second and third law methods. Dissociation energies of the metal monochlorides were evaluated by reference to AgCl, leading to the values at 298 K in kcal/mol-1: CrCl, 90.3; MnCl, 80.9; FeCl, 78.8; CoCl, 80.7; NiCl, 90.1; all ±1.6 kcal mol-1. Entropies and enthalpies of sublimation of the solid dichlorides were derived from sublimation pressures measured by the torsion-effusion method. Sublimation enthalpies lead to MCl2 dissociation energies that are in close agreement with values derived from the mass spectrometric results; D(MCl2) values at 298 K are CrCl2, 179.3; MnCl2, 188.3; FeCl2, 190.1; CoCl2, 182.6; and NiCl2, 178.2; all ±1.0 kcal mol-1. Vapor entropies evaluated from the sublimation data show that the electronic energy levels of the doubly-charged free metal ions provide a reasonable representation of the electronic entropies of the metal dichlorides; in addition, the entropy data are consistent with a bent structure for CrCl2, but with linear structures for the other dichlorides. Judging from the second and third law agreement for the monochloride exchange reactions, the M+ free ion electronic levels also seem appropriate for the transition metal MCl species. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Equilibria involving the gaseous mono- and difluorides of Sc, Y, and La were studied by effusion-beam mass spectrometry, and reaction enthalpies were derived by second and third law methods. In addition, the sublimation pressures of the crystalline trifluorides ScF3, YF3, and LaF3 and related thermodynamics of the gaseous trifluorides were determined by the torsion-effusion method. Dissociation energies at 298 K in kcal mol-1 for the bonds M–F, FM–F, and F2M–F, respectively, were derived as follows: For Sc, 143.2±3.2, 148.8±4.1, and 155.7±6.4; for Y, 163.8±3.2, 145.6±3.2, and 151.6±4.7; and for La, 157.5±4.1, 153.2±3.2, and 149.2±5.4. These values do not fall into any obvious pattern. The dissociation energies of ScF and YF are in good agreement with the results of high-level theoretical calculations. Spectroscopic and molecular constants of the species are summarized, and the thermochemical results are compared with values in the literature. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The gaseous species SiO(OH) and SiO(OH)2 were detected as products of the reaction of SiO2(l) and H2O(g) near 2000 K, using effusion-beam mass spectrometry. No other silicon-containing hydroxides or oxyhydroxides were observed. From third law analysis of equilibrium data, values of Δ[sub f]H°[sub 298] of SiO(OH) and SiO(OH)2 were evaluated as -118 and -213 kcal mol-1, respectively, both ±4 kcal mol-1. Several equilibrium measurements on gaseous SiO2 yielded a Δ[sub f]H°[sub 298] value of -67 kcal mol-1, which is 6–10 kcal mol-1 less stable than values given in most compilations. It appears that the new thermochemical data for SiO(OH) and SiO(OH)2, plus a literature estimate for Si2O(OH)6, can be used to model the equilibrium behavior of the silica–steam system over a wide range of temperatures and pressures. [ABSTRACT FROM AUTHOR]

Effusion cell beams containing the gaseous species HPO, HPO2, HPO3, and POBr along with other products were generated by the reaction of H2O(g) or Br2(g) with Ca2P2O7(s). The species were identified by mass spectrometry, and were characterized thermochemically from the study of several reaction equilibria. Reaction enthalpies and standard enthalpies of formation were derived from third law analysis of the equilibrium data, yielding the Δ[sub f]H[sup °][sub 298] values HPO, -34.2; HPO2, -110.6; HPO3, -168.8; and POBr, -53.5, all in kcal mol-1. Our new result for POBr is in serious disagreement with a value reported in the literature; there are no previous reports on the other species studied here. A preliminary Δ[sub f]H[sup °][sub 298] value of -60.2 kcal mol-1 was also obtained for POCl(g), this time in reasonable accord with a literature value. The new thermochemical data yield calculated compositions in agreement with measured values for some lamp gas mixtures. [ABSTRACT FROM AUTHOR]

The reactive vaporization of MnO(c) in the presence of O2 and H2O/D2O has been studied by effusion-beam mass spectrometry, and the new species MnO2, MnOH, Mn(OH)2, and MnO(OH) have been identified. The identities of the hydroxides were confirmed from deuterium isotopic substitution. Reaction enthalpies and standard enthalpies of formation have been derived from equilibrium measurements, yielding the Δ[sub f]H°[sub 298] values for the gaseous species MnO2, -17.6; MnOH, 0.1; Mn(OH)2, -95.9; and MnO(OH), -41.1, all in kcal mol-1. For use in the analysis, thermal functions were calculated from known or estimated molecular constants. Bond energies derived from the results fall in a logical and consistent sequence. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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○0(BaI) =76.2±1.5 kcal mol-1 and D○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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

High temperature gaseous equilibria involving the molecular species UBr, UBr2, UBr3, UBr4, and UBr5 were studied by mass spectrometry over wide temperature ranges; reaction enthalpy data were derived primarily from second-law analysis. From this information, the individual bond dissociation energies and the standard enthalpies of formation of the U–Br species were derived with an accuracy of about 8 kJ mol-1. The derived bond dissociation energies at 298 K in kJ mol-1 are as follows: D °(U–Br)=377; D °(BrU–Br)=435; D °(Br2U–Br)=430; D °(Br3U–Br)=348; and D °(Br4U–Br)=166. Trends in these values are similar to those found in the U–Cl system, but quite different from those of the U–F system. Absolute entropies evaluated from the equilibrium data indicate significant electronic contributions for the lighter species, decreasing markedly on approaching UBr5. Trends in the bond dissociation energies and electronic entropies of the fluorides, chlorides, and bromides are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Provides information on the chemical vapor deposition of YBa[sub2]Cu[sub3]O[sub7-x] superconducting thin films. Range of values for various deposition parameters; Synthesis of the barium, yttrium and copper compounds; characterization of the resulting films using x-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy and thermal resistivity.