Trends of Atmospheric CCl 3 F,CCl 2 F 2 and CCl 2 FCClF 2 in Shanghai (China)

Atmospheric concentrations of CCl 3 F (CFC-11), CCl 2 F 2 (CFC-12), and CCl 2 FCClF 2 (CFC-113) in troposphere in Shanghai, China (31°1N) have been routinely monitored by using gas chromatography with electron capture detector from November 1997 to December 2000. The observation shows that there is a slowly declining trend of the three compounds. On the other hand, a comparison has been drawn between the concentrations observed and the ones calculated by 2-box model on the basis of the global statistical data of CFCs production and emission. Our observation agrees with the calculations. It shows that production and emission of chlorofluorocarbons (CFCs) in China are still at a low level and gradually decreasing.     

Electron-impact ionization of CCl4 and CCl2F2

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3(+), CCl2(+), CCl+, C+, Cl2(+), and CCl3(2+) from CCl4; and for production of CCl(2)F+, CClF2(+), CClF(+), (CCl+ + CF2(+)), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2(+),Cl+) and (CCl+, Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is +/- 5-7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch-Mark theory reproduces the experimental cross sections correctly for both targets.     

Rotational diffusion in aprotic and protic solvents

We present the orientational relaxation times in protic and aprotic solvents for rose bengal in its lowest excited singlet state. The method uses a mode locked dye laser for polarized excitation, and time correlated single photon counting for determination of the time resolved polarized fluorescence. The observed orientational decay for the dipolar aprotic solvents and the alcohols are in agreement with the values predicted by the Stokes-Einstein diffusion equation. In the latter solvents, volume and shape corrections must be made for attachment of the alcohol to the two anion sites of the dye molecule. The solvent N-methylformamide, however, shows rose bengal reorienting much faster than the alcohols. Our interpretation of this data suggests that agreement with the Stokes-Einstein equation (stick boundary conditions) is coincidental. We propose a solvent torque model in which the solvent interaction at each anion site of rose bengal controls the deviations from an expected slip boundary condition. This qualitative model is used to correlate our data as well as relevant data in the literature. The values in picoseconds for the observed orientational relaxation times are given in parenthesis; acetone (70), DMF (160), DMSO (420), MeOH (190), EtOH (450), isopropanol (840), NMF (500).     

Rotational relaxation characteristics of the monoclinic phase of CCl4

We present a study of crystalline CCl(4) spanning up to 10 orders of magnitude in time at temperatures ranging from 160 K to 190 K using molecular dynamics simulations. The relaxation process is studied using angular self correlation functions. The results show that each of the four nonequivalent molecules of the monoclinic phase have a particular relaxation time. Two of the molecules relax in an exponential way and the two other molecules have a more complex behavior, especially at the lower temperatures. In all cases, the molecular rotations correspond to quick jumps between equivalent tetrahedral equilibrium positions. Most of these rotations are about the C(3) symmetry axes, however at high temperatures, rotations about the C(2) symmetry axes are observed as well. The waiting time between rotations follows a Poisson distribution. The calculated relaxation times show an Arrhenius behavior with different activation energy for different nonequivalent molecules, in line with recently published findings of nuclear quadrupole resonance experiments.     

Rotational diffusion of compressed gaseous monodeuteromethane

The rotational correlation functions, calculated from the ν₂ (A₁) infrared absorption band of CH₃D compressed with various gases, has been compared with those computed by the Gordon M or J models. The J model gives the most accurate fit to the experimental results.     

Rotational diffusion tensors for non-spherical molecules

The rotational diffusion tensors of several rigid molecules are determined from the rotational friction tensor. The molecular friction tensor is modeled as a sum over the translational Stokes law friction coefficients of the constituent atoms of the molecule. Agreement of the theory with experimental rotational diffusion constants and onentational correlation times is surprisingly good.     

Rate coefficients and ClO radical yields in the reaction of O(1D) with CClF2CCl2F,CCl3CF3, CClF2CClF2, and CCl2FCF3

Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(¹D) with CClF₂CCl₂F (CFC‐113) (k₂), CCl₃CF₃ (CFC‐113a) (k₃), CClF₂CClF₂ (CFC‐114) (k₄), and CCl₂FCF₃ (CFC‐114a) (k₅) at 296 K are reported. Rate coefficients for the loss of O(¹D) were measured using a competitive reaction technique, with n‐butane (n‐C₄H₁₀) as the reference reactant, employing pulsed laser photolysis production of O(¹D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k₂ = (2.33 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.61 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₄ = (1.42 ± 0.25) × 10^?10 cm³ molecule^?1 s^?1, and k₅ = (1.62 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 43: 393–401, 2011     

Spectroscopic properties of trichlorofluoromethane CCl(3)F calculated by density functional theory

Density functional theory is used to generate local potential energy surfaces in normal coordinates for several chlorine isotopomers of trichlorofluoromethane (CCl(3)F, CFC11). An examination of predicted structures suggested that the PBE0 functional would be suitable. Anharmonic surfaces around the equilibrium geometries are reported, as determined by energies, gradients, and second derivatives. Vibrational levels for fundamentals, overtones and combination bands are reported, as well as harmonic frequencies, anharmonic constants, rotational constants, isotope shifts, and infrared intensities. These are compared with experimental information.     

Vibrational analyses and barriers to internal rotation of CH3CCl2F and CH3CHClF

The i.r. spectra of gaseous and solid CH₃CCl₂F and CH₃CHClF have been recorded from 140 to 4000 cm⁻¹. The corresponding Raman spectra of the liquids have also been recorded and depolarization values have been measured for the CH₃CCl₂F molecule. Also the Raman spectrum of gaseous CH₃CHClF has been recorded. All spectra have been interpreted in detail and the 18 normal vibrations of both molecules have been characterized. Hot bands of the internal torsional mode for CH₃CCl₂F were observed at 248(2 ← 1) and 232 cm⁻¹ (3 ← 2) in the far-i.r. spectrum of the gas. These frequencies are in good agreement with those calculated using the 4·42 kcal/mole barrier obtained in an earlier Raman study. The internal torsional mode for CH₃CHClF was observed at 261 cm⁻¹ in the spectra of the solid and the three-fold periodic barrier was calculated to be 4·38 kcal/mole. The barriers are compared in a series of chloro, fluoro and bromo substituted ethane derivatives.     

Chain photoreduction of CCl3F in TiO2 suspensions: enhancement induced by O2

Trichlorofluoromethane (CFC 11) was photoreduced in aqueous suspensions of TiO2 particles containing HCO2- ions and air. Dissolved O2 inhibited the reaction during an induction period that preceded the rapid formation of chloride ions. Reaction rates were higher in systems containing O2 as compared to analogous reactions that occurred in anaerobic suspensions. High photonic efficiencies of Cl- formation (> or =15) were achieved using suspensions with pH > or = 5. As was the case for studies with air-free suspensions, reactions are best described using a photoinitiated chain mechanism that produced CHCl2F and Cl- during the propagation steps. The enhanced yields obtained in the presence of air are attributed to the removal by O2 of electrons trapped in the oxide, which are converted first into H2O2 and then into reducing radicals that participate in the chain process. Enhanced yields of Freon photoreduction were also observed during illumination of air-free suspensions containing hydrogen peroxide, which were interpreted using a similar mechanism.     

Rotational dynamics and conformational kinetics in liquid crystals

Abstract

Two particular aspects of solute dynamics in ordered media are analysed on the basis of the solution of multivariate diffusion equations: the effects of the solvation dynamics on the rotational motions of dipolar probes in liquid crystal solvents, and the alteration of reaction pathways in isomerization kinetics caused by the solvent order. The introduction of a suitable solvent coordinate allows the interpretation of high frequency contributions in the rotational correlation functions observed by spectroscopic techniques, namely dielectric dispersion, IR and Raman spectroscopy, ESR lineshapes and optical Kerr effect. For molecular systems undergoing conformational changes, a method is offered to evaluate the modification of the torsional barriers resulting from the anisotropic torques modulated by the molecular shape changes along the reaction coordinate.     

Rotational dynamics and conformational kinetics in liquid crystals

Two particular aspects of solute dynamics in ordered media are analysed on the basis of the solution of multivariate diffusion equations: the effects of the solvation dynamics on the rotational motions of dipolar probes in liquid crystal solvents, and the alteration of reaction pathways in isomerization kinetics caused by the solvent order. The introduction of a suitable solvent coordinate allows the interpretation of high frequency contributions in the rotational correlation functions observed by spectroscopic techniques, namely dielectric dispersion, IR and Raman spectroscopy, ESR lineshapes and optical Kerr effect. For molecular systems undergoing conformational changes, a method is offered to evaluate the modification of the torsional barriers resulting from the anisotropic torques modulated by the molecular shape changes along the reaction coordinate.     

Rotational diffusion of colloidal particles near confining walls

We study the rotational diffusion of a spherical colloid confined in a narrow channel between parallel plane hard walls. The walls damp translational diffusion much more than rotational diffusion so that there is expected to be little translation-rotation coupling. Using a recent calculation of the nonisotropic rotational mobilities arising from the hydrodynamic interactions with the walls, we set up the rotational Smoluchowski equation for either a particle with a permanent dipole moment or a polarizable particle with axisymmetric polarizabilities subject to an external electric field. Using the Smoluchowski equation dynamics we calculate the time-correlation functions of orientation that are measured in depolarized light scattering for the cases of no external field, external field normal to the walls, and external field parallel to the walls. The decay of correlations is shown to be given by a weighted sum of decaying exponentials and can be characterized by an initial and a mean characteristic decay time. The weights and decay rates of each component and the characteristic decay times are studied numerically for a range of field strengths. The nonisotropic rotational mobilities make these decay times highly sensitive to the distance of the particle from the confining walls. This position dependence can be used as a method of measuring the rotational mobilities or, conversely, the rate of decay of correlations can be used as a probe of particle position between the confining walls.     

The plastic and liquid phases of CCl3Br studied by molecular dynamics simulations

We present a molecular dynamics study of the liquid and plastic crystalline phases of CCl(3)Br. We investigated the short-range orientational order using a recently developed classification method and we found that both phases behave in a very similar way. The only differences occur at very short molecular separations, which are shown to be very rare. The rotational dynamics was explored using time correlation functions of the molecular bonds. We found that the relaxation dynamics corresponds to an isotropic diffusive mode for the liquid phase but departs from this behavior as the temperature is decreased and the system transitions into the plastic phase.     

Rotational diffusion of dyes in micellar media from transient absorption

Solubilizer effects in dye solutions have been investigated by subnanosecond laser-pulse photometry. Different models for the transient dichroism of dye-micelle solutions are proposed. Computer fits of the experimental curves indicate that the model where dye molecules rotate within the liquid-like interior of the micelles is the most realistic one. Since the measured rotational diffusion times differ for different dyes in almost the same way as for pure highly-viscous solvents, the dye molecules do not act merely as labels for the rotation of the micelles, but rotate themselves considerably. It is shown that the rotational diffusion of dye molecules and micelles can be separated giving reasonable results for the size of the micelles. The results are compared with previous steady-state experiments.     

The kinetics of radiation-induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclohexene

The kinetics of hydrogen abstraction from cyclohexene by CCl₃ radicals were studied in CCl₄ solution as a function of cyclohexene concentration and temperature in the range of 26–140°C. The CCl₃ radicals were produced both by radiolysis of CCl₄ and by photolysis of CCl₃Br. The rate constant for the reaction was found to be given by the equation where θ = 2.303 RT kcal/mol. This activation energy leads to C? H bond strength for the allylic hydrogen of 85 ± 1 kcal/mol, which means a resonance stabilization energy of 11 ± 1.5 kcal/mol for the C-C₆H₁₁ radical.     

Positron diffusion in liquid metals

We introduce the effective Lagrangian with spontaneously broken density in the Sethna-Sachdev-Nelson formula, and propose one explanation for the increase of the positron diffusion lengthL ₊ in the liquid metal phase with temperature. It is shown that the effective mass of the positron in the liquid metal phase will decrease due to the restoration of the spontaneously broken density around the positron, when temperature increases.     

Deactivation of I(2P1/2) by CH3Cl,CH2Cl2, CHCl3, CCl3F,and CCl4

Collisional deactivation of I(²P_1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH₃Cl, CH₂Cl₂, CHCl₃, CCl₃F, and CCl₄ are 3.1±0.3×10⁻¹³, 1.28±0.08×10⁻¹³, 5.7±0.3×10⁻¹⁴, 3.9±0.4×10⁻¹⁵, and 2.3±0.3×10⁻¹⁵cm³ molecule⁻¹ s⁻¹, respectively, at room temperature (298 K). The higher efficiency observed for relaxation by CH₃Cl, CH₂Cl₂, and CHCl₃ reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm⁻¹) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799–803, 1998