Products, rate constants and mechanisms of gas-phase reactions of CX(3)(+), CX(2)(+), CX(+) (X = F and/or Cl) and Cl(+) with 1,1,1- and 1,1,2-trichlorotrifluoroethane.

The gas-phase ion chemistry of 1,1,1- and 1,1,2-trichlorotrifluoroethane was investigated with an ion trap mass spectrometer. Following electron ionization both compounds (M) fragment to [M - Cl](+), CX(3)(+), CX(2)(+), CX(+) (X = F and/or Cl) and Cl(+). The reactivity of each of these fragments towards their neutral precursors was studied to obtain product and kinetic data. Whereas [M - Cl](+), CCl(3)(+) and CCl(2)F(+) cations are unreactive under the experimental conditions used, all other species react via halide abstraction to give [M - Cl](+) and, to a far lesser extent, [M - F](+). In addition, CX(2)(+) ions form CClX(2)(+) in a process which formally amounts to chlorine atom abstraction, but more likely involves chloride ion abstraction followed by charge transfer. CX(+) ions also form minor amounts of CX(3)(+) product ions, possibly via chloride abstraction followed by or concerted with dihalocarbene elimination from the (incipient) [M - Cl](+) ion. Trivalent carbenium ions are less reactive than divalent species, which in turn are less reactive than the monovalent ions (reaction efficiencies are given in parentheses): CF(3)(+)(0.70) < CF(2)(+)(0.78) < CF(+)(0.96). More interestingly, within each family of ions reactivity increases with the number of fluorine substituents (e.g. CF(2)(+) > CFCl(+) > CCl(2)(+) and CF(+) > CCl(+)), i.e. reactivity increases with the ion thermochemical stability, as measured by available standard free enthalpies of formation. Evaluation of the energetics involved shows that reactions are largely driven by the stability of the neutrals more than of the ions. Finally, the products observed in the reaction of Cl(+) are attributed to ionization of the neutral via charge transfer and fragmentation.     

Observation of the singlet oxygen dimol emission from neodymium laser pumped oxygen in the gas phase and in 1,1,2-trichlorotrifluoroethane solution

Dimol emission $\text{2}\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{<mtext>g</mtext>}}\text{) → 2}\text{O}{}_2\text{(}{}^3\text{Σ}{}_{\mathrm{<mtext>g</mtext>}}{}^{\mathrm{?}}\text{) + hν}{}_{\mathrm{<mtext>633</mtext><mtext>nm</mtext>}}$ has been observed from neodymium glass laser pumped oxygen in the gas phase and in 1,1,2-trichlorotrifluoroethane solution. The emission lifetime is dependent on quenching by ground state oxygen, and the quenching rate constants determined in this work are consistent with literature values.     

Integrated absorption intensities of haloethanes and halopropanes

The infrared absorption intensities of the chlorofluorocarbons C₂Cl_xF_y, (x + y = 6); the hydrofluorocarbons C₂H_xF_yH (x + y = 6); and a number of hydrochlorofluorocarbons, including some members of the propane series, have been measured. Absorption intensities have been obtained by integration over specified ranges of frequencies. The ranges used include the atmospheric window (1250t-833 cm⁻¹), 3500-450 cm⁻¹, 1300-700 cm⁻¹, and those for selected individual absorption bands. Comparisons of the results have been made with published work where available, and attention is drawn to possible sources of error in the measurement of band areas. The spectra of the halopropanes have been included for the range 3500-150 cm⁻¹. A preliminary study has been made of the relation between the number of fluorine atoms in the molecule and the intensity of absorption of the CF stretching vibrations.     

Normal coordinate and infrared band intensities of trichloronitromethane and trichloroacetate ions

Laser Raman and IR spectra in the region 50–3000 cm⁻¹ for trichloronitromethane and trichloroacetate ions were recorded. All observed vibrational bands have been assigned to normal modes. Normal coordinate analyses of these molecules have been carried out in the valence force-field approximation. A set of force constants was obtained leading to good agreement between observed and calculated frequencies. The relative displacements of the atoms resulting from normal coordinate calculations were used to compute the IR band intensity of each mode by the CNDO/2-MO procedure. The intensity calculations confirmed the assignments and supported the calculated force constants.     

Electrochemical Catalysis of the Reduction of 1,1,2-Trifluorotrichloroethane (Freon 113) by Outer-Sphere Electron Transfer Mediators

Cyclic voltammetry and preparative electrolysis in DMF were used to study the electrochemical catalytic reduction of 1,1,2-trifluorotrichloroethane with aromatic electron transfer mediators (p-dicyanobenzene, p-diacetylbenzene, fluoranthen, perylene, and (E)-azobenzene), leading to trichloroethylene in high yield. The results of a kinetic study of these systems indicate that the efficiency of other mediators of this class may be estimated relative to their redox properties. In comparison with direct electrochemical reduction of Freon 113, the use of aromatic electron transfer agents significantly raises the efficiency of Freon conversion and permits us to perform the reaction at less negative potentials.     

Analysis and prediction of absorption band shapes, fluorescence band shapes, resonance Raman intensities, and excitation profiles using the time-dependent theory of electronic spectroscopy

A general method for the simulation of absorption (ABS) and fluorescence band shapes, resonance-Raman (rR) spectra, and excitation profiles based on the time-dependent theory of Heller is discussed. The following improvements to Heller's theory have been made: (a) derivation of new recurrence relations for the time-dependent wave packet overlap in the case of frequency changes between the ground and electronically excited states, (b) a new series expansion that gives insight into the nature of Savin's preresonance approximation, (c) incorporation of inhomogeneous broadening effects into the formalism at no additional computational cost, and (d) derivation of a new and simple short-time dynamics based equation for the Stokes shift that remains valid in the case of partially resolved vibrational structure. Our implementation of the time-dependent theory for the fitting of experimental spectra and the simulation of model spectra as well as the quantum mechanical calculation of the model parameters is discussed. The implementation covers all electronic structure approaches which are able to deliver ground- and excited-state energies and transition dipole moments. The technique becomes highly efficient if analytic gradients for the excited-state surface are available. In this case, the computational cost for the simultaneous prediction of ABS, fluorescence, and rR spectra is equal to that of a single excited-state geometry optimization step while the limitations of the short-time dynamics approximation are completely avoided. As a test case we discuss the well-known case of the strongly allowed 1 (1)A(g) --> 1 (1)B(u) transition in 1,3,5 trans-hexatriene in detail using method ranging from simple single-reference treatments to elaborate multireference electronic structure approaches. At the highest computational level, the computed spectra show the best agreement that has so far been obtained with quantum chemical methods for this problem.     

Analysis of band intensities in the IR spectra of macromolecular assemblies

Band intensities in the IR spectra of oscillator chain assemblies are calculated. It is shown that the dependences of the band intensity on temperature and on the concentration of the second conformation are nonlinear and are determined by the orientation of the vector of the oscillator dipole moment derivative with respect to the extension coordinate along the rotation axis. In the case of vibrations of the main chain, for bands with perpendicular dichroism, the contributions to the band intensity from the change in the orientation of the vector of the oscillator dipole moment derivative with respect to the extension coordinate and from the change in the vibration shape are compensated by each other. Bands with parallel dichroism, for which this compensation is absent, are more sensitive to changes in the chain conformation. This approach is illustrated by analysis of the vibrational spectra of isotactic and syndiotactic polymethyl methacrylate and polyethylene terephthalate. Institute of Construction Engineering, Kazan. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 359–365, March–April, 1995. Translated by I. Izvekova     

Spectral Characteristics and Transformations of Intermediates in Irradiated Freon 11, Freon 113, and Freon 113a

Optical absorption bands observable in Freon 11, Freon 113, and Freon 113a irradiated at 77 K were assigned to various intermediates (radical cations, radical ion pairs, and complexes of radicals with ions). The transformations of these species in thermal and photochemical reactions occurring at 77 K were studied. On the basis of experimental results, it was suggested that the radical anions of Freon 11 and Freon 113 are unstable at 77 K and the spatial distribution of the intermediates produced is inhomogeneous.     

Study on the i.r. band intensities of cyclopropane

The i.r. absorption intensities of cyclopropane-h₆ and -d₆ were measured in the gas phase using the pressure broadening technique. The obtained band intensities were analysed in order to determine the intensity parameter (∂p/∂S_j) with the help of information from the Coriolis interaction and CNDO/2 calculation. It has proved that the Coriolis interaction can offer important information even for a couple of bands which are mutually removed far away. In case of C₃H₆, despite 400 cm⁻¹ distance between the ν₉ and ν₁₀ bands, the product ζ^z_9a,10b(∂p^x/∂Q_9a)(∂p^y/∂Q₁₀b) has been determined as positive. In this way the sign of (∂p/∂Q_i) has been clearly decided for cyclopropane, and consequently the value of (∂p/∂S_j) has been definitely determined.Further, by investigating the present results with those previously obtained, for many other related molecules, the following general rule has been found about the relationship between the sense of displacement vector of hydrogen atom group and the enhanced dipole moment vector induced thereby. Namely, the directions of these two vectors are opposite for the stretching vibrational modes and the same for almost all deformation vibrational modes of hydrogen atoms.     

Rotational spectroscopy and molecular structure of 1,1,2-trifluoroethylene and the 1,1,2-trifluoroethylene-hydrogen fluoride complex

Fourier transform microwave rotational spectra in the 6-22 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen fluoride, including the normal isotopomer, the two singly substituted 13C species, and the complex obtained with DF. A unique planar structure for the complex is determined from a combined analysis of the rotational constants derived from the spectra and atomic positions obtained using Kraitchman [Am. J. Phys. 21, 17 (1953)] substitution coordinates. Consistent with this structure, no hyperfine splitting of rotational lines due to the nuclear quadrupole coupling interaction is observed for the D-containing species. Although the primary interaction in the complex is a hydrogen-fluorine hydrogen bond, as is the case for all previously studied Lewis acid-fluoroethylene complexes, the CF2CHF-HF complex adopts a distinctly different geometry in which both the primary and secondary interactions occur between the HF molecule and a F atom and a H atom, respectively, bonded to the same carbon of CF2CHF. The 2.020(41) A hydrogen bond has hydrogen fluoride as the donor and 1,1,2-trifluoroethylene as the acceptor and forms a 109.0(13) degrees C-F...H angle. The secondary interaction between the hydrogen fluoride F atom and the H atom geminal to the acceptor F atom causes the hydrogen bond to deviate 41.6(51) degrees from linearity. Structural comparisons with analogous complexes formed with mono- and difluorinated ethylenes suggest that the primary hydrogen bond strength and the fluoroethylene fluorine atom basicity both decrease with increasing fluorine substitution. In the course of this work, it was necessary to obtain additional rotational spectra for the 1,1,2-trifluroethylene monomer and to improve the precision of the values of the structural parameters for this molecule.     

Conditions of measurement of infrared absorption band intensities by fourier transform spectrometry

The influence of infrared spectra of some different conditions required in the use of modern FTIR spectrometers has been studied. This work has been performed in two ways: firstly, the influence of factors such as apodization function, level of zero filling, number of data points and phase correction procedure is determined from experimental data, and, secondly, numerical simulation of the whole process has been carried out in order to separate experimental error from that deu to the mathematical treatment.     

Effect of the components of the raman scattering tensor on band intensities

The Raman scattering (RS) tensor as a function of excitation radiation frequency is studied taking into account, the vibration quantum. It is shown that the corresponding asymmetric components of the tensor are described by fast converging series. Expressions are obtained for the antisymmetric and symmetric components of the RS tensor. A convenient formula is proposed for the calculation of the RS tensor and its components, where the tensor is represented as a sum of the derivative of static polarizability and the terms containing fast converging series. The formula makes it possible to avoid infinite summation. Computer experiments simulating the dependence of the intensity of RS bands and their components on the excitation frequency are carried out. Moscow State University of Building Engineering. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1006–1015, November–December, 1996. Translated by I. Izvekova     

Crystalline sulfur dioxide: Crystal field splittings,absolute band intensities,and complex refractive indices derived from infra-red spectra

The infra-red absorption spectra of thin crystalline films of sulfur dioxide at 90 K are reported in the 2700-450 cm⁻¹ region. The observed multiplicity of the bands in the regions of fundamental modes is attributed to crystal field effects, including factor group and LO—TO splittings, and naturally present minor ³⁴S, ³⁶S and ¹⁸O substituted isotopic species. Complex refractive indices determined by an iterative Kramers—Kronig analysis of the extinction data, and absolute band strengths derived from them, are also reported in this region.     

Integrated IR and Raman intensities of aliphatic alcohols in the liquid phase

Integrated molar IR intensities of normal aliphatic alchols, methanol to n-heptanol, are computed by integration of the Lorentz local field corrected function V·(ν·ε″) over the wavenumber interval covered by the absorption band. Raman intensities are measured with the divided cell technique and external standards and the corresponding local field corrections are applied before integration. Absolute values for the integrated IR intensities and relative values for the integrated Raman intensities are given of the OH-stretch and CO-stretch vibrations.     

Radiation-induced dehalogenation of 1,1,1,2 tetrachloroethane and 1,1,2 trichloro-1 bromoethane reactions of 1,1,2 trichloroethyl radicals

The kinetics of the radiation-induced free radical chain reactions in solutions of CCl₃CClH₂ and CCl₂BrCH₂Cl in cyclohexane (RH) were studied in the temperature range of 90–225°C. 1,1,2 trichloroethyl and 1,1,1,2 tetrachloroethyl radicals were produced by the reaction of radiolytically generated cyclohexyl (R) radicals with solutes. The reactions studied were The following rate expressins were obtained: where θ = 2.303RT in kcal/mole. From the activation parameters of the k₄/k₅ rate constant ratio and the assumption that E₄ = E, E₅ was calculated to be 20.2 ± 0.2 kcal/mole. The Arrhenius parameters for the Cl atom elimination reaction from chloroethyl radicals derived from liquid and gas-phase studies are compared.     

Infrared band intensities and bond polarities: Part 4. The bond-bending vibration of acetylene

Bond moment theory which takes rehybridization effects into account is used to analyze the band intensity of the π_u vibrational mode of acetylene. A value of μ_b(C XXX H) = 0.82 D is obtained which is in accord with that of ≈0.22 D, sense C XXX H, previously obtained for the CH bond in ethylene.     

Influence of intramolecular hydrogen bonding on OH-stretching overtone intensities and band positions in peroxyacetic acid

Vapor phase absorption spectra and integrated band intensities of the OH stretching fundamental as well as first and second overtones (2ν(OH) and 3ν(OH)) in peroxyacetic acid (PAA) have been measured using a combination of FT-IR and photoacoustic spectroscopy. In addition, ab initio calculations have been carried out to examine the low energy stable conformers of the molecule. Spectral assignment of the primary features appearing in the region of the 2ν(OH) and 3ν(OH) overtone bands are made with the aid of isotopic substitution and anharmonic vibrational frequency calculations carried out at the MP2/aug-cc-pVDZ level. Apart from features associated with the zeroth-order OH stretch, the overtone spectra are dominated by features assigned to combination bands composed of the respective OH stretching overtone and vibrations involving the collective motion of several atoms in the molecule resulting from excitation of the internal hydrogen bonding coordinate. Integrated absorption cross section measurements reveal that internal hydrogen bonding, the strength of which is estimated to be ～20 kJ/mol in PAA, does not result in a enhanced oscillator strength for the OH stretching fundamental of the molecule, as is often expected for hydrogen bonded systems, but does cause a precipitous drop in the oscillator strength of its 2ν(OH) and 3ν(OH) overtone bands, reducing them, respectively, by a factor of 165 and 7020 relative to the OH stretching fundamental.     

Relative electronegativities of carbon,silicon and germanium as indicated by band intensities of MHCl3 molecules

Liquid state dispersion curves of SiHCl₃ and GeHCl₃ from 5000 to 450 cm^?1 have been obtained, and band intensities of the ν₁, ν₄ and ν₅ vibrations derived. These values are compared with literature data for CHCl₃, and the trends discussed in relation to the electronegativities of the elements. Evidence is provided that germanium is more electronegative than silicon or tin in accord with the views of Sanderson.