D.L. Hildenbrand

Thermochemistry of molecular FeO, FeO+ and FeO

Abstract The gaseous oxides FeO and FeO 2 were identified by mass spectrometry as components of the effusion beam from a cell containing, initially, solid Fe 2 O 3 . From studies of gaseous equilibria involving these species, the dissociation energies D 0 0 (FeO) = 96.8 ± 3 kcal (4.20 ± 0.13 eV) and D 0 0 (FeO 2 ) = 199.0 ± 5 kcal (8.64 ± 0.22 eV) were derived. The ionization potential of FeO was found to be 8.71 ± 0.10 eV, leading to D 0 0 (Fe + -O) = 78.2 ± 4.6 kcal (3.39 ± 0.20 eV).

Mass spectrometric studies of the thermochemistry of gaseous TiO and TiO2

Abstract Several gaseous reaction equilibria involving TiO and TiO 2 were studied by mass spectrometry and the results were used to derive the dissociation energies of the two titanium oxides. Isomolecular exchange reactions of TiO with AIO and BaO gave highly concordant results leading to D O O (TiO) = 662.7 ± 6.3 kJ/mol (6.87 ± 0.07 eV), which combines with other recent work to establish firmly D O O (TiO). For TiO 2 , the heat of atomization, D O O (TiO 2 ), was derived as 1271.9 ± 11.7 kJ/mol (13.18 ± 0.12 eV). From electron impact threshold measurements, the ionization potentials of TiO and TiO 2 were found to be 6.70 and 9.54 eV, respectively, both ± 0.10 eV. The thermochemical data for TiO and TiO + are in accord with the relatively small cross section observed for the process Ti + O → TiO + + e at thermal energies.

Dissociation energy and ionization potential of the molecule CF

Abstract The gaseous equilibrium S + CF 2 = SF + CF was studied over the temperature range 1851 to 2232 K by mass spectrometry, and the derived enthalpy change was used to evaluate the heat of formation of CF Δ H 298 = 58.0 ± 2.4 kcal/mol (2.52 ± 0.10 eV), and the dissociation energy D 0 0 (CF) = 130.8 ± 2.4 kcal/mol (5.67 ± 0.10 eV). The new thermochemical data indicate a slightly higher stability for CF than earlier determinations. Direct measurement by electron impact yielded a value of 9.17 ± 0.10 eV for the vertical ionization potential of CF, in agreement with an indirect result obtained from the photodissociative ionization of C 2 F 4 .

Vapor pressure determination of arsenic activity in a molten Cu-Fe-S matte

The activity of As in a molten copper smelting matte of composition 35.0 mass pct Cu, 35.8 mass pct Fe, and 29.9 mass pct S has been derived from vapor pressure measurements at 1336 K. The initial As doping level was 1.6 mass pct. Mass spectrometry showed the principal vapor phase species to be As2; smaller amounts of AsS and S2 were also present. The activity coefficient of As in the matte, γ (As), was found to have the value 0.7 ±0.2 (mole fraction)-1 in the composition range studied. Activity values found in the present study were an order of magnitude smaller than those determined by an isopiestic method, and were about two orders of magnitude greater than those derived from measurements of As distribution between copper and white metal. The vapor pressure method is believed to be more direct and reliable; sources of error in the various methods are discussed.

Dissociation energy of the PdO molecule

Abstract Mass spectrometric studies of the gaseous equilibrium Pd+Oxa0⇌xa0PdO yield the dissociation energy D 0 o (PdO)=56±3 kcal mol −1 . This new value is significantly lower than one recommended in the most recent review, D 0 o (PdO)=90±20 kcal mol −1 , where an earlier value near 55 kcal mol −1 was rejected because of higher values ranging from 90 to 98 kcal mol −1 for neighboring metal monoxides. It is shown that the lower value reported here is consistent with the unique closed-shell structure of the Pd atom.

Vertical ionization potential of the CF2 radical

Abstract The CF 2 radical was generated in an equilibrium effusion cell by the reaction of gaseous SF 6 with carbon at 1550 K. From electron impact threshold measurements, the vertical IP of CF 2 was found to be 11.54 ± 0.10 eV. This value is lower than previous electron impact results, but it is consistent with data obtained from dissociative photoionization threshold measurements via a thermochemical cycle.

The dissociation energy of AsO from gaseous equilibrium measurements

Abstract The gaseous exchange reaction As + SnO = AsO + Sn was studied by mass spectrometry (1408–1487 K), yielding the dissociation energy D 0 0 (AsO) = 4.92 ± 0.08 eV. This agrees closely with a spectroscopic result from the B state of AsO, corroborating the interpretation of the band spectra. Reanalysis of the ground-state vibrational levels yields a similar value of D 0 0 (AsO).

Dissociation energy of the molecule GeCl

Abstract Mass spectrometry was used to identify the gaseous species GeCl, CuCl, Ge, and Cu in a molecular beam issuing from an effusive source, and to evaluate the equilibrium constant for the monochloride exchange reaction in the range 1543–1776 K. From the derived reaction enthalpy, the dissociation energy, D 0 o , of GeCl was evaluated as 92.5 ± 2.3 kcal mol −1 . The thermochemical value is lower than a spectroscopic value derived from a short extrapolation of vibrational levels in the 4 Σ − state, indicating a potential maximum of about 7 kcal mol −1 in that state.

Vaporization studies of calcium arsenate under neutral conditions and in contact with copper pyrometallurgical slags

.The feasibility of capturing As as calcium arsenate in reverberatory and Mitsubishi converter slags used in copper pyrometallurgy was studied by torsion-effusion, thermogravimetric, and mass spectrometric methods. In the temperature range from 1376 to 1489 K pure Ca3 (AsO4)2 decomposed to yield very low equilibrium pressures of AsO and O2. Mixtures of Ca3 (AsO4)2 with slag exhibited rapid mass losses between 973 and 1173 K. The vapor phase species evolved under these conditions were As2 and As4, indicating that the arsenate had been reduced by the slag to volatile elemental arsenic.