32SF6 dissociation rate during irradiation by a tea CO2 laser

A new experimental method is presented for measuring the multiple-photon dissociation rate of SF₆. It appears that there is a reverse process which associates the photofragments into SF₆. The measured dependence of the dissociation probability versus laser flux seems to agree qualitatively with theoretical models.     

The thermal dissociation of the [Co(NH3)6]Cl3 and [Co(NH3)6]Br3 complexes in vacuo

The thermal dissociation of the complexes, [Co(NH₃)₆]X₃(X^?=Cl, Br), was studied in vacuo using the techniques of thermogravimetry, evolved gas analysis and mass spectrometric analysis. It was found that the reaction stoichiometry was identical to that previously determined in air but that the type of intermediate compounds formed were different. The dissociation occurred by the reactions:

     

The thermal dissociation of the [Co(en)3](SCN)3 and [Co(en)3]I3 complexes

The thermal dissociation of the [Co(en)₃](SCN)₃ and [Co(en)₃]I₃ complexes was studied by thermogravimetry, differential thermal analysis, thermomagnetic analysis, pyrolytic techniques, evolved gas analysis, and mass spectrometry, in vacuo and nitrogen atmospheres. It was found that the [Co(en)₃](SCN)₃ complex dissociated in four steps:

It was not possible to elucidate the intermediate compounds formed in the thermal dissociation of the [Co(en)₃]I₃ complex.     

The H2 elimination reactions of Ã2B3g C2H4+ and C2D4+

Kinetic energy releases from the unimolecular H₂ (D₂) elimination reactions of energy-selected òB_3gC₂H₄⁺(C₂D₄⁺) have been obtained by a photoelectron-photoion coincidence technique. The energy releases suggest a 1,1 elimination and are compatible with the presence of a small reverse activation energy barrier of the order of 0.02 eV. Such a barrier was indicated by a detailed ab initio study of this dissociation and the present results are discussed in the light of this theoretical treatment.     

SF6-sensitized dissociation of UF6 with a pulsed CO2 laser

The dissociation of UF₆ sensitized by SF₆ excited with a pulsed CO₂ laser in the presence of H₂ and CO as scavengers has been investigated. In the SF₆-UF₆-H₂ system the dissociation yields have been determined as a function of the laser frequency, the fluence, and H₂ partial pressure. A maximum dissociation yield has been found at a laser frequency of 935 cm^?1. No obvious dissociation of UF₆ was observed in the UF₆-SF₆ system without F-atom scavengers.     

TEA CO2 laser-induced reaction of CH3NO2 with CF2HCl: A mechanistic study

Dissociation of nitromethane has been observed when a mixture of CF₂HCl and CH₃NO₂ is irradiated using pulsed TEA CO₂ laser at 9R (24) line (1081 cm^-1), which is strongly absorbed by CF₂HCl but not by CH₃NO₂. Under low laser fluence conditions, only nitromethane dissociates, whereas at high fluence CF₂HCl also undergoes dissociation, showing that dissociation occurs via the vibrational energy transfer processes from the TEA CO₂ laser-excited CF₂HCl to CH₃NO₂. Time-resolved infrared fluorescence from vibrationally excited CF₂HCl and CH₃NO₂ molecules as well as UV absorption of CF₂ radicals are carried out to elucidate the dynamics of excitation/dissociation and the chemical reactions of the dissociation products.     

The thermal decomposition reactions of [Co(en)3](NO3)3 and [Co(en)3](HSO4)3

The thermal decomposition reactions were determined for [Co(en)₃](N0₃)₃ and [Co(en)₃(HSO₄)₃ in a dynamic nitrogen gas atmosphere and _vacuo, where en represents ethylenediamine. Data were obtained using thermogravimetry, DTA, thermomagnetic analysis, and mass spectrometry. The dissociation reactions in nitrogen were found to be as follows:

and

In vacuo, the dissociation process for [Co(en)₃](N0₃)₃ is the same as in nitrogen. Also, the decomposition of [Co(en)₃](HSO₄)₃ is the same except for the first step which is:

     

Determination of dissociation degrees of K3NbF8 and K3TaF8 by thermodynamic analysis of subsystems of the KF-K2NbF7 and KF-K2TaF7 systems

A special form of the LeChatelier-Shreder equation describing the equilibrium between the crystalline phase and the melt in system A-AB in which the substance AB partially dissociates upon melting was applied to systems KF-K₃NbF₈, K₂NbF₇-K₃NbF₈ and to KF-K₃TaF₈, K₂TaF₇-K₃TaF₈ subsystems of the binary systems KF-K₂NbF₇ and KF-K₂TaF₇ in which the additive compounds K₃NbF₈ and K₃TaF₈ are formed. Using the phase diagram of the system KF-K₂NbF₇ determined by McCawley and Barclay (1971) and the values of the fusion enthalpy of K₃NbF₈ taken from literature, the intervals of the dissociation degree values of K₃NbF₈ for both branches of the liquidus curve of K₃NbF₈ were calculated. The calculated values of the dissociation degree depend on the coordinates of the liquidus curve of K₃NbF₈ of the pertinent phase diagram, on its used branch and section, and on the value of the fusion enthalpy of K₃NbF₈. For the measured fusion enthalpy of K₃NbF₈ (57 kJ mol⁻¹), a common interval of the dissociation degree values of K₃NbF₈ for both branches of the liquidus curve of K₃NbF₈ is 0.71–0.72. Similarly, intervals of the dissociation degree values of K₃TaF₈ for both branches of the liquidus curve of K₃TaF₈ were calculated using the phase diagram of the system KF-K₂TaF₇ determined by Boča et al. (2007) and the measured fusion enthalpy of K₃TaF₈ ((52 ± 2) kJ mol⁻¹). The error of the determination of the fusion enthalpy of K₃TaF₈, the common interval of the dissociation degree values of K₃TaF₈ for both branches of the liquidus curve of K₃TaF₈ is 0.68–0.69.     

Infrared spectra of KNaSO4 and K3Na(SO4)2

The infrared spectra, transmittance and polarized reflectance, of KNaSO₄ and K₃Na(SO₄)₂ are reported. Group theoretical analysis was carried out and a vibrational assignment proposed on basis of C_3v and D_3d symmetries. Factor group and site effects are discussed.     

Infrared spectra of Ag2BrNO3 and Ag2ClNO3

The infrared spectra of Ag₂BrNO₃ and Ag₂ClNO₃ are reported. Vibration assignments are proposed on the basis of the group theoretical analysis and D_2h symmetry. Factor group, site and TO-LO splittings are observed. The internal and external mode frequencies are correlated with those of AgNO₃ and KNO₃(II).     

Laser isotope separation in SF6

Laser induced isotope separation in SF₆ and SF₆ mixtures has been investigated in a collisionally dominated pressure regime. Experimental results with SF₆/rare gas mixtures point out the importance of collision induced dissociation following the initial collisionless dissociation. Rotational relaxation induced by rare gases and H₂ is shown to play a signficant role in the dissociation of both isotopic species. Total vibrational relaxation (V-T/R) induced by H₂ as a collision partner is shown to dominate the dissociation efficiency of SF₆/H₂ mixtures.     

First-principles study of O2 adsorption and dissociation on the CuCr2O4 (100) surface

The adsorption and dissociation of molecular oxygen on spinel CuCr₂O₄ (100) surface were carried out by first-principles calculations based on density functional theory (DFT). The calculated results indicate that the Cr site is most favorable for atomic oxygen adsorption, with an adsorption energy of 402.8 kJ/mol. For molecular oxygen adsorption, there are three types of favorable interaction modes: O₂ forms bonds with the Cu site or O₂ binds to two Cr sites or O₂ interacts with both Cu and Cr sites simultaneously. The lowest activation energy (E_a = 35.4 kJ/mol) was found through exploring possible reaction pathways for O₂ dissociation. The relationship between E_a and reaction enthalpy (ΔH) for O₂ dissociation adsorption reactions fits Brønsted-Evans-Polanyi (BEP) behavior.     

Near-UV photodissociation of gaseous UF6 in the presence of H2

Mixtures of UF₆ and H₂ in different ratios have been irradiated at 360 and 400 nm by means of a filtered mercury lamp. A significant pressure drop has been observed at both excitation wavelengths due to the dissociation of UF₆ into UF₅+ F. A very high dissociation quantum yield has been found.     

Normal modes of the MoO2−4 ion in Tb1.8Eu0.2(MoO4)3 single crystal

Polarized Raman spectra (single crystal) at 300 K and infrared spectra (powder) at 300 and 77 K in the region 250–1000 cm^?1 of a binary molybdate of terbium and europium have been recorded. Based on C_2v symmetry, group theoretical analysis has been carried out and a vibrational assignment is proposed.     

Sulfation of CuO,Fe2O3, MnO2, and NiO with (NH4)2SO4

An attempt has been made to calculate the free energy values for possible reactions utilising the available thermodynamic data in order to study the sulfation of CuO, Fe₂O₃, MnO₂ and NiO with (NH₄SO₄, and further trials have been made to determine the exact reaction through differential thermal analysis. There is no real correlation between the theoretical value of ΔH° and that calculated from the DTA peak, which may be due to some uncertainty in the thermodynamic values and the possibility of some side reactions.     

Infrared photolysis of C2F4S2: a comparison of multiphoton dissociation models

Infrared multiphoton dissociation of the planar ring compound

has been shown to yield two CF₂S molecules. The threshold for dissociation using the R(16) transition of the 9.6 μm CO₂ laser is 0.12 J/cm². At fluences above 1 J/cm³ dissociation is accompanied by the emission of light in the 300–750 nm region. The fractional dissociation per pulse and the average energy deposition have been measured as functions of laser fluence, laser wavelength, C₂F₄S₂ pressure, and added argon pressure. The variations of the fractional dissociation with fluence and absorbed energy are compared to the predictions of two models. The first model is based on the assumption of a Planck distribution for the dissociating C₂F₄S₂ molecules, while the second is based on a rate equation approach to the dissociation. Both models predict that the dissociating parent compound has a rather broad vibrational distribution.     

The dissociation energies of gaseous Br2 and I2

New rotational analyses have been made of the B³Π_0⁺u—X¹Σ⁺_g systems of ⁷⁹Br₂, ⁸¹Br₂ and ¹²⁷I₂. The density of vibrational states near the dissociation limit in the upper states follows the LeRoy—Bernstein predictions for n = 5. From short extrapolations, the ground state dissociation energies are found to be: D₀(⁷⁹Br⁸¹Br) = 15895.6 cm^?1, D₀(¹²⁷I₂) = 12440.1 cm^?1.     

An electrical conductivity (EC) study of the thermal dissociation of [Co(NH3)6]X3 and [Co(en)3]X3 complexes

The thermal dissociation of the [Co(NH₃)₆]X₃ (X = Cl^?, Br^?, I^?, and NO^?₃), [Co(en)₃]X₃ (X = Cl^?, Br^?, I^?, NO^?₃, HSO^?₄ and $\text{1}\text{2}$ C₂O^2?₄), cis- [Co(en)₂Cl₂]Cl, and trans-[Co(en)₂ClBr]NO₃ complexes was investigated by an electrical conductivity (EC) technique. During the thermal dissociation reactions, liquid or semi-liquid phases are formed which cause large increases in the EC of the compound. The effect of concentration of the complex in a matrix medium as well as the composition of the matrix material on the EC curves were also determined.     

Phase relations and thermodynamic properties in the ternary reciprocal system LiFNaFNa3AlF6Li3AlF6

The ternary reciprocal sytem LiFNaFNa₃AlF₆Li₃AlF₆ has been investigated by thermal analysis, differential thermal analysis, quenching, X-ray diffraction, microscopy, and calorimetry. The phase diagrams of the following systems are given: LiFNaF (revised), LiFAlF₃, Na₃AlF₆LiF, and LiFNaFNa₃AlF₆Li₃AlF₆. Some values of heat of mixing and heat content in the system have been measured.It is shown that molten mixtures in this system can be treated as consisting of the following species: Li⁺, Na⁺, AlF^3-₆, AlF₃ and F^-. At high contents of alkali fluoride the dissociation of the AlF^3-₆ ion to AlF₃ and F^- will, however, be negligible.On the basis of the calorimetric data, heats of mixing and dissociation, together with the degree of dissociation of AlF^3-₆, in the systems LiFAlF₃ and LiFNa₃AlF₆ have been calculated. The partial Gibbs free energy, enthalpy and entropy of Na₃AlF₆ in the system LiFNa₃AlF₆ have also been calculated. Finally the activity of Na₃AlF₆ in the latter system has been calculated by treating it as a part of the ternary reciprocal system 3LiF+Na₃AlF₆→Li₃AlF₆+3NaFA satisfactory agreement between the Flood, Førland and Grjotheim theory and the experimental values is obtained at small Na₃AlF₆ concentrations.     

Potential energy surfaces for the photodissociation H2O→O(1Dg + H2(X1Σ+g)

The minimum energy pathways for symmetrical dissociation of water into O(¹D_g + H₂(X¹Σ⁺_g) are calculated by the MRD Cl technique for various excited states of H₂O and possible mechanism for the photodissociation are discussed.