Laser induced energy-transfer studies in polyatomic mixtures: CH3F−CH3Cl

The rate of vibration energy transfer from CH₃F excited to the v₃ = 1 C—F stretching vibration to CH₃Cl has been measured by monitoring the rate of rise time of the CH₃Cl v₃ C-Cl stretch at 732 cm^?1 subsequent to laser pumping of the CH₃F. The V–V crossover rate was determined to be 35 ± 5 msec^?1 torr^?1 in mixtures of CH₃F-CH₃Cl and 48 ± 9 msec^?1 torr^?1 in mixtures of CH₃F-CH₃Cl and 40 torr of argon. The measured rate is interpreted in terms of the near resonant process

and is well in line with several predited and measured near resonant V–V crossovers between unlike collision partners. The possibility of obtaining an optically pumped three level infrared laser in CH₃Cl at 13.7 μ (corresponding to the v₃, ground state transition) is also discussed.     

The kinetics of vibrational energy transfer and relaxation processes in matrix isolated CH3F

Subsequent to exciting v₃ by a CO₂ laser pulse, fluorescence has been detected from 2v₃ of CH₃F trapped in rare gas matrices. 2v₃ is activated by V-V energy transfer and deactivates at twice the rate of v₃ relaxation. A kinetic model is presented to interpret these observations.     

Raman spectrocopic studies on the vibrational relaxation of CH3CN in different environments

Comparison of the frequencies and half-widths of v₁ in a variety of solvents shows that dispersion forces make a significant contribution to the effective intermolecular potential. Measurements of τ_v^?1 and [ω²] in the CH₃CN/CD₃OD/CCl₄ system demonstrates that long-range (hydrogen-bonding?) potentials significantly affect the relaxation rate.     

Vibration-vibration energy transfer iln CH3F

Previous works have reported vibration-vibration and vibration-translation transfer rates in CH₃F and CH₃FX mixtures. In this letter we report the study of the fast VV transfer rate populating the 3ν₃, ν₁ and ν₄ states of CH₃F. Gaseous CH₃F was initially excited to the ν₃ state by a TEA CO₂ laser operating on the P(20 9.6 μ line and collisional pumping to the 3ν₃, ν₁ and ν₄ states was measured by monitoring the rise time of the fluorescence at 300 cm⁻¹. The rate constant was found to be 2.2 × 10⁵ sec⁻¹ torr⁻¹.     

Fluorine core esca linewidths in CH3F and CF4

Ab initio calculations within the Hartree-Fock formation have been carried out on potential energy surfaces of the ground and the F_1s hole states of CH₃F and CF₄ in order to investigate linewidths of their ESCA spectra. The calculations show that potential energy surfaces of both hole states have dissociative character and can be approximated by straight lines in the region of interest. A simple formula for the ESCA fwhm linewidth is derived which yields results in good agreement with experiment. Theoretically derived relaxation and Koopmans' energies have been investigated as a function of geometry.     

Die gas-chromatographische Analyse von Fluormethanen (CF4, CHF3, CH2F2, CH3F)

Ohne Zusammenfassung     

CH3F absorption of the CO2-laser emission measured by the photoacoustic technique

Spectra of coincidence of CH₃F IR absorption with CO₂-laser emission at pressures of 2, 10 and 60 Torr were recorded by the use of a photoacoustic detection method in the whole range of CO₂-laser emission. The spectra show that CH₃F absorbs many CO₂-laser lines in the range 1084–1071 cm⁻¹ with the strongest absorption at 1046.80cm⁻¹, laser line P(20). Absorption is predominantly due to the fundamental of v₃, which is well spread over the whole laser emission range. The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of the line spectrum, characteristic of lower pressure samples, disappears as pressure is increased.     

AB initio calculations of CH3OH vibrational force constants

SCF equilibrium geometry, population analysis and vibrational force constants of the CH₃OH molecule have been determined ab initio using the SCF LCGO method. A fair agreement with experiment is found. The main result is the asymmetry of the methyl group.     

Theoretical calculational studies on the mechanism of thermal dissociations for RN3 (R=CH3, CH3CH2, (CH3)2CH, (CH3)3C)

Mechanisms of RN₃ (R=CH₃, CH₃CH₂, (CH₃)₂CH, (CH₃)₃C) dissociations are proposed based on CAS, MP2 and B3LYP methods. The energy gaps between the ground-state reactants RN₃ and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, ¹RN₃ → ¹RN + ¹N₂. The ISC point, therefore, is considered as a transition state of the spin-forbidden reactions, ¹RN₃ → ³RN + ¹N₂. The methods of IRC and topological analysis of electron density are used to explain and predict the thermal dissociation pathways of the reactions studied.     

Reactivity of Cl(2P1/2) atoms towards CH3F

The photochlorination of methyl fluoride has been studied at low pressures. Excited (²P_1/2) chlorine atoms have been found to participate in the reaction. The ratio of the excited and ground state rate constants has been estimated at room temperature.

---

. (²P_1/2) . .

     

The synthesis and vibrational spectra of the antimony(V)fluoride-fluorosulfates SbF3(SO3F)2, SbF4(SO3F) and Sb2F9(SO3F)

The synthesis of the title compounds by a variety of routes is described. These routes involve the oxidation of antimony(III)fluoride by bis(fluorosulfuryl)peroxide and the use of non-statistical ligand redistribution reactions. Complex formation with ClO₂SO₃F leads to ClO₂[SbF_n(SO₃F)_6-n], with n=3 or 4. Polarized Raman data and low temperature infrared data are reported. All antimony(V)fluoride-fluorosulfates are found to have fluorosulfate bridges with SbF₃(SO₃F)₂ and SbF₄(SO₃F) being polymers. Ionic formulations for the ClO⁺₂ complexes are again based on vibrational spectra.     

Binding energies of CH3F and CH2F2 calculated by the overlapping sphere SCF MS Xα method

Multiple scattering Xα calculations with overlapping spheres were performed on CH₃F and CH₂F₂ for all-valence region ionization potentials. Comparison with previous Xα calculations shows a substantial improvement.     

Very low thermal expansion in TaO2F

X-ray diffraction data for TaO₂F from 20 to 400 K show a thermal expansion so low that we cannot be certain whether it is positive or negative. We estimate the absolute value of the thermal expansion coefficient to be less than 6×10⁻⁷/K. This then is comparable to that of amorphous SiO₂ and is apparently unique behavior for a cubic material over such a large temperature range.     

Collision-assisted multiple step excitation of CH3F by irradiation with a TEA CO2 laser

By irradiating a mixture of CH₃F highly diluted in Ar with a TEA CO₂ laser, the v₃ overtone emission rises with a rate much larger than the “up-the-ladder” V-V pumping rate indicating that the CH₃F is excited up to the 3v₃ level almost instantly. This occurs via multiple step excitation assisted by rotational transitions in collisions.     

Esr studies on the γ-irradiated acetone-CCl3F system

γ-irradiated acetone in polycrystalline CCl₃F at 77 K has been studied by ESR to reveal that the acetone molecules tend to be oriented in CCl₃F Matrix upon freezing the solution in ESR tubings. At higher concentrations both monomer and dimer radical cations of acetone are produced. The dimer cation is responsible for the optical absorption with λ_max ≈ 740 nm.     

Electric and magnetic properties of CO,HF, HCI,and CH3F

Electric multiple moments polarizabilities and magnetizabilities of CO, HF, HCI, and CH₃F are calculated using SCF wavefunctions and coupled Hartree-Fock perturbation method. The A and G tensors are also calculated and discussed in relation to electric-induced differential scattering and electric-field-gradient-induced birefringence in these gases.     

Reactivity of electronically excited Br(2P1/2) atoms towards CH3F

The rate constants for Br(²P_1/2) and Br(²P_3/2) atoms in the reaction Br+CH₃FHBr+CH₂F in photobromination of CH₃F have been determined. Their ratio is 10^{–(2.6±0.5)} exp(10100±1000/RT) in the temperature range of 60–200 °C.

---

Br(²P_1/2) Br(²P_3/2) Br+CH₃FHBr+CH₂F CH₃F. 60–200 °C 10^{–(2,6±0,5)} exp (10100±1000/RT).

     

Ab initio molecular orbital study on the gas phase SN2 reaction F + CH3Cl → CH3F + Cl

Ab-initio molecular orbital (MO) and direct ab initio dynamics calculations have been applied to the gas phase S_N2 reaction F⁻ + CH₃Cl → CH₃F + Cl⁻. Several basis sets were examined in order to select the most convenient and best fitted basis set to that of high-quality calculations. The Hartree–Fock (HF) 3−21+G(d) calculation reasonably represents a potential energy surface calculated at the MP2/6−311++G(2df,2pd) level. A direct ab initio dynamics calculation at the HF/3−21+G(d) level was carried out for the S_N2 reaction. A full dimensional ab initio potential energy surface including all degrees of freedom was used in the dynamics calculation. Total energies and gradients were calculated at each time step. Two initial configurations at time zero were examined in the direct dynamics calculations: one is a near collinear collision, and the other is a side-attack collision. It was found that in the near collinear collision almost all total available energy is partitioned into two modes: the relative translational mode between the products (40%) and the C − F stretching mode (60%). The other internal modes of CH₃F were still in the ground state. The lifetimes of the early- and late-complexes F⁻ … CH₃Cl and FCH₃ … Cl⁻ are significantly short enough to dissociate directly to the products. On the other hand, in the side-attack collision, the relative translation energy was about 20% of total available energy.     

The vibrational spectra of CD3SH and CD3SD in various phases and of CH3SH and CH3SD in the torsion vibration region of the two solid phases

Knowledge of the vibrational spectra of CH₃SH, CH₃SD, CD₃SH and CD₃SD is expanded. Measurements of liquid CD₃SH and CD₃SD correspond to a former determination of an inverse vapor pressure isotope effect, even though association exists. Investigation of the four solid compounds in the low-frequency range permit identification of the torsion modes of the low-temperature phase as doublets between 200 and 400 cm⁻¹. The splitting of these doublets by 100 and 60–70 cm⁻¹ is as large as for solid methylamine and methanol, but differs from the alcohol and cannot be explained exclusively by intermolecular coupling. Like the splitting of the close-spaced doublets of the SH or SD stretching vibrations, it is caused partly by coupling and partly by the presence of different types of sites of the unit cell. Corresponding to the changed crystal structure and to the weaker hydrogen bonding, the torsion modes of the high-temperature phase appear as triplets or quartets at lower wave numbers.     

PVTx measurements for N2O + CH3F, N2O + CH2F2, and N2O + CHF3 binary systems

Isochoric PVTx measurements have been performed for the binary system of nitrous oxide + CH₃F (R41), +CH₂F₂ (R32), and +CHF₃ (R23) using a new experimental set-up. The experiments covered both the two-phase region and the superheated vapor region and were performed within the temperature range 214–358 K and within a pressure range from 270 to 5600 kPa. Data have been collected for not less than four compositions for each system. The vapor–liquid equilibrium data were derived correlating the experimental data by means of the Carnahan–Starling–De Santis equation of state. The studied systems show a positive deviation from the Raoult's law. The results obtained were compared with the Burnett PVTx data. The two methods showed a mutual consistency within an acceptable margin of error. No other experimental PVTx data were found in the literature for these binary systems.