Electronic spectra and predissociation of jet-cooled CH3O and CH3O-Ar in the Ã2A1 state

The òA₁-X̃²E electronic spectrum of jet-cooled methoxy radical has been examined by the LIF technique. Two newly discovered vibrational bands of 2930 and 1390 cm⁻¹ are assigned to ν₁ (totally symmetric C-H stretching) and a degenerate ν₅ mode, respectively. The predissociation, CH₃O → CH₃ + O in the òA₁ state is newly elucidated and the threshold energy is deter- mined as 5100 cm⁻¹ from the potential minimum. For the CH₃O-Ar complex, the threshold energy is reduced by about 100 cm⁻¹.     

The photoacoustic spectra of substituted benzenes in the near infrared region—I

The photoacoustic spectra of three benzonitriles, five acetophenones and three benylbromides were recorded using the commercial EDT OAS 400 photoacoustic spectrometer in the near i.r. region, i.e. 3850–10000 cm⁻¹ (2.6−1.0 μm). A combined study of the mid and far i.r. absorption spectra with the near i.r. PAS spectra led to a provisional assignment of the observed PAS peaks as combinations of fundamentals and overtone bands.     

Unexpected phase transformation from VO2(R) to VO2(A) during hydrothermal treatment in the V2O5�CH2C2O4�CH2O system

Vanadium dioxide (VO₂) was directly synthesized via the reduction of V₂O₅ with oxalic acid adopting two different types of hydrothermal processes in the temperature ranging from 180 to 260 °C. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In all these processes, the VO₂(B) phase was first formed at a relative lower temperature or the initial stage at higher temperature and then it transformed to the VO₂(R) phase with the increase of temperature. The building-block-stacking mechanism was proposed to elucidate the transformation from VO₂(B) nano-plates to snowflake-like VO₂(R) powders. During this transformation, no trace of the VO₂(A) phase was observed when one-step hydrothermal treatment method was used, whereas some part of the branches of the snowflake-like VO₂(R) particles transformed to metastable VO₂(A) nanofibers in the autoclave during cooling process when the two-step hydrothermal treatment method was conducted. The reason for this transformation can be contributed to the defects formed during the stacking process.     

Derivative analysis of Raman spectra of liquid water in the OH (D) stretching region

Second derivative analysis of Raman spectra of H₂O, D₂O and HOD in liquid phase at room temperature for parallel and perpendicular polarized modes in the OH and OD stretching regions is reported. Five components obtained at approximately 3215, 3375, 3455, 3535 and 3640 cm⁻¹ for the second derivative plots of Raman spectra of liquid water are explained as due to the presence of three types of associated water species with (i) both OH bonds involved in moderately strong hydrogen bonds (SS), (ii) both OH bonds involved in weak hydrogen bonds (WW), and (iii) one OH bond involved in strong and one in weak hydrogen bonds (SW) respectively. The derivative plots obtained for Raman spectra of D₂O and HOD also contain features expected to be present on the basis of this model.     

Determination of the Activity Coefficients of NaCl in the System NaCl–NH4Cl–H2O

Using ion-selective electrode(s) (ISE) the activity coefficients of NaCl in the system NaCl–NH₄Cl–H₂O at 10, 25, and 40°C were measured by a computer-controlled automatic titration system. The ionic strength fractions of NH₄Cl were 0.2, 0.4, 0.6, and 0.8, respectively. It was found that the influence of the NH₄⁺ cation on the Na glass ISE was small enough to be neglected up to 3.0 mol-kg^-1. The Pitzer equation was adopted to calculate the activity coefficients of NaCl in this system and compared with the experimental data. Comparison of results indicates that the Pitzer parameters correlated from solubility data are suitable for calculating the activity coefficients for this system within the saturated solutions.     

Thermodynamics for fluid mixtures near to and far from the vapor–liquid critical point

To describe thermodynamic properties of fluid mixtures near to and far from the vapor–liquid critical point, we need a method where a classical equation-of-state is augmented with a correction based on renormalization group (RG) theory. The advantage of the method described here is that, subject to well-defined assumptions, it can be applied not only to binary mixtures but to mixtures containing any number of components. While our method is based on White’s recursion procedure, our extension to mixtures is based on the isomorphism assumption and on an approximation suggested by Kiselev. To illustrate, calculations are presented for the critical loci of some alkane mixtures containing one discrete component and one pseudo-component whose composition is characterized by a continuous distribution of molecular weight. While critical loci calculated with the RG correction are similar to those calculated by the classical equation-of-state alone, inclusion of the RG correction provides better agreement with experiment.     

Thermodynamic properties of crystalline polymeric C60 phases in the temperature region from O → 0 to 340 E

The temperature dependences of the heat capacity C _p° = f(T) were studied in an adiabatic vacuum calorimeter for the orthorhombic, tetragonal, and rhombohedral polymeric C₆₀ phases in the 7—340 K temperature interval with an error of 0.2%. Comparative analysis of C _p° of these phases formed by stacking of one-dimensional and two types of two-dimensional polyfullerenes C₆₀, was performed, and their fractal dimensionalities D were determined for temperatures below 50 K. The thermodynamic functions of the crystalline polymeric C₆₀ phases were calculated in the temperature region from O 0 to 340 K: C _p°(T), H°(T) — H°(0), S°(T) — S°(0), and G°(T) — H°(0). Assuming that S°(0) = 0, the standard entropies of formation _f S° of these phases from graphite at T = 298.15 K and standard pressure were calculated. In addition, the entropies of transformation of the initial face-centered cubic phase of fullerite C₆₀ in the crystalline polymeric C₆₀ phases and entropies of their interconversions under the same conditions were estimated. The thermodynamic characteristics of the polymeric C₆₀ phases were reviewed.     

Spectroscopic analysis of asymmetric top free radicals——Application to pure rotational spectra of NO_2 in the ground vibronic state

Several key problems involved in the analyses of spectra of asymmetric top molecules, i.e., the effective Hamiltonian, the representation and basis vector, identification of energy levels, the selection rules, the relative intensity, and Zeeman tuning rate, were elucidated systematically. Introducing the high-order centrifugal distortion terms into the effective Hamiltonian, the precision for calculation has been improved substantially, which allows us to analyze the high-lying rotational transitions. A global analysis of all available spectra of 14N16O2 in the ground vibronic state has been made to obtain a set of molecular constants of 14N16O2 in the ground vibronic state which is the most precise and extensive so far. Using the improved parameters, some FIR LMR lines left unassigned hitherto have been identified successfully.     

Direct Synthesis of Acetic Acid from CH4 and CO2 in the Presence of O2 over a V2O5-PdCl2／Al2O3 Catalyst

The possibility of synthesizing acetic acid from CH4 and CO2 in the presence of O2 over a V2O5-PdCl2/Al2O3 catalyst has been explored. The result shows that it is feasible in catalyzing a direct conversion of CH4, CO2 and O2 to acetic acid. It is concluded that both CO2 and O2 are involved in the formation of acetic acid.     

The Nature of Conformational Polymorphism in the Crystals of Ph3Sb(O2CCH2–CH=CH2)2

Russian Journal of Coordination Chemistry - Crystallization of the Ph3Sb(O2CCH2?CH=CH2)2 complex upon fast solvent (benzene) evaporation gives monoclinic crystals (I), whereas in the case of...     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—II

The theory of factor analysis developed in Part I [A. Muller and D. Steele, Spectrochim. Acta 46A, 817 (1990) [1] is extended to cases where m > 3, m being the number of factors. The effect of increasing the number of independent parameters by m(m-1) for T′ and the subsequent changes produced in the transformed eigenspectra, are investigated. Applications to actual spectra of mixtures of: (A) butan-2-one, ethyl ethanoate, cyclohexane and oct-1-ene (B) butan-2-one, ethyl ethanoate, cyclohexane and 2-methylpentane and (C) oct-1-ene, butan-2-one, ethyl ethanoate, cyclohexane and 2-methyl-pentane are presented. Using standard target techniques, an alternative approach is developed for the m> 3 case. This is based on transformation of the leading three eigenspectra, followed by identification and elimination of a component in a repetitive manner, until completion. The problems associated with the implementation of the Beer-Lambert Law are explored the need for accurate determination of a suitable wavenumber block to ensure the removal of the correct amount of each component, is examined. The ability to recognize at least one of the m component spectra per programme cycle is demonstrated.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—I

The theory of factor analysis is extended to permit the computer based extraction of the spectra of pure components from spectra of mixtures. A simultaneous linear, non-orthogonal transformation of the eigenspectra and eigenvectors is used to generate all positive absorbances and concentrations within noise level. Applications to actual spectra of mixtures of: (A) ethyl ethanoate, butan-2-one and oct-1-ene; (B) ethyl ethanoate, butan-2-one and cyclohexane; and (C) butan-2-one, cyclohexane and 2-methylpentane are presented. The effects of changes in signs of the constrained diagonal elements of the transformation matrix is investigated. To explore the ability of the software to cope with component spectra in which there are no wavenumbers at which one component dominates an artificial set of mixtures is examined. Recognizable spectra are extracted. It appears that, even when there are no wavenumbers at which one component dominates, the condition of finding “the sum of squares of negative absorbances/concentrations” near zero is adequate to yield useful spectra for library searches.     

Modelization of vibrational spectra beyond the harmonic approximation from an iterative variation–perturbation scheme: the four conformers of the glycolaldehyde

This paper presents the computed anharmonic frequencies and IR intensities in the mid-infrared region for the four conformers of glycolaldehyde (Cis cis, Trans trans, Trans gauche and Cis trans forms). The fundamental transitions and their connected overtones and combination bands through strong anharmonic couplings (Fermi resonances) are provided. The results are stemmed from an iterative variational–perturbational resolution of the vibrational problem implemented in the VCI-P code. The four potential electronic surfaces are built as a Taylor series truncated to the fourth order around each minimum geometry. The second derivatives with respect to the normal coordinates were computed at the CCSD(T)/cc-pVTZ level, while the third and fourth derivatives were estimated with the B3LYP/6-31 + G(d,p) model chemistry. For the most stable Cc form, an average deviation of about 10 cm⁻¹ is obtained with respect to the unambiguous experimental values. Furthermore, some of the transitions observed in the CH stretchings region were reassigned. The theoretical values calculated for the Tt and Tg forms are compared to the experimental data obtained from the irradiation of the Cc conformer isolated in Ar matrix with an IR source.     

Thermochemistry and kinetics of the 2-butanone-4-yl CH3C(=O)CH2CH2• + O2 reaction system

Thermochemistry and kinetic pathways on the 2-butanone-4-yl (CH₃C(=O)CH₂CH₂•) + O₂ reaction system are determined. Standard enthalpies, entropies, and heat capacities are evaluated using the G3MP2B3, G3, G3MP3, CBS-QB3 ab initio methods, and the B3LYP/6-311g(d,p) density functional calculation method. The CH₃C(=O)CH₂CH₂• radical + O₂ association reaction forms a chemically activated peroxy radical with 35 kcal mol⁻¹ excess of energy. The chemically activated adduct can undergo RO−O bond dissociation, rearrangement via intramolecular hydrogen transfer reactions to form hydroperoxide-alkyl radicals, or eliminate HO₂ and OH. The hydroperoxide-alkyl radical intermediates can undergo further reactions forming ketones, cyclic ethers, OH radicals, ketene, formaldehyde, or oxiranes. A relatively new path showing a low barrier and resulting in reactive product sets involves peroxy radical attack on a carbonyl carbon atom in a cyclic transition state structure. It is shown to be important in ketones when the cyclic transition state has five or more central atoms.     

The analysis of high-resolution spectra of the ν2 and ν5 bands of CH335Cl and CH337Cl

The ν₂ and ν₅ bands of CH³₃⁵Cl and CH³₃⁷Cl between 1300 and 1600 cm⁻¹ have been analysed using a Fourier transform spectrum with 0.006 cm⁻¹ resolution. For CH³₃⁵Cl, the microwave data and 1200 lines from the IR spectrum with J⩽ 50 were fitted with an overall r.m.s. error of 0.00079 cm⁻¹ using the method of predicative observations. A similar fit for 900 lines of CH³₃⁷Cl gave an overall r.m.s. error of 0.00055 cm⁻¹, providing erroneous microwave data on the ν₅ level are omitted. Improved molecular constants are reported for both isotopic species. As expected, the values for ν₂ and ν₅ are little affected by chlorine isotopic substitution.