Manifestation of resonance dipole-dipole interaction in spectra of low-temperature molecular mixtures of C2F6 in CF4 and CF4 in C2F6

We have measured IR absorption spectra of solutions C₂F₆ in CF₄ (T = 178 K) and CF₄ in C₂F₆ (T = 173 K) in the overtone range of the spectrum. We have studied how the resonance dipole-dipole interaction affects the formation of contours of bands that correspond to transitions to states involving the vibrations ν₁₀(C₂F₆) and ν₃(CF₄), which are strong in the dipole absorption. For the system C₂F₆ in liquid CF₄, the state ν₂ + ν₁₀(C₂F₆) resonantly interacts with the state ν₂(C₂F₆) + ν₃(CF₄), and, for the system CF₄ in liquid C₂F₆, the state ν₁ + ν₃(CF₄) resonantly interacts with the state ν₁(CF₄) + ν₁₀(C₂F₆). The contours of the bands ν₂ + ν₁₀ (C₂F₆) in the spectrum of the mixture with CF₄ and of the bands ν₁ + ν₃(CF₄) in the spectrum of the mixture with C₂F₆ have been calculated.     

Water–Surfactant Contact Studied byF–H Heteronuclear Overhauser Effect Spectroscopy

Intermolecular¹⁹F–¹H cross-relaxation is measured using heteronuclear Overhauser effect NMR spectroscopy (HOESY) in the micellar solution of cesium pentadecafluorooctanoate. The results are analyzed in terms of a weak¹H–¹⁹F cross-relaxation between the water protons and the fluorines in the fluoroalkyl chain and a strong¹⁹F–¹⁹F cross-relaxation within the fluoroalkyl chain. The water–surfactant cross-relaxation indicates a water approach to the first CF₂segment in the order of 2.0 Å and a short (?ns) water residence time. Evidence of fluorine hydration further inside the micelle is presented.     

Vapor phase infrared spectrum of CF3Cl in the region 4.8–16 μm

The gas phase infrared spectrum of CF₃Cl was studied at medium resolution in the range 2100-600 cm^?1. A high number of bands including fundamental, overtone, combination, and “hot” bands of the two species, CF₃³⁵Cl and CF₃³⁷Cl, with natural isotopic abundance, was identified. The frequency values of the two long-wavelength fundamentals, ν₃ and ν₆, were evaluated with higher accuracy by differences of suitable combination and “hot” bands. The Q-branch rotational structure of the ν₂ + ν₅ perpendicular band for the main variety was analyzed and the molecular constants obtained are reported.     

Absorption spectrum of the (CF4) dimer in liquid argon solution

The concentration dependence of the shape of absorption bands in the spectrum of CF₄ in liquid argon is studied in the concentration range (0.01–17)×10^?3 molar fractions at 93 K. In all spectral regions related to ν₃, the shape of the spectral function is determined, along with the Fermi resonance 〈ν_i,ν₃+1,ν₄|≈〈νi,ν₃,ν ₄+2|, by the resonance dipole-dipole interaction. In the spectral region of the Fermi doublet ν ₁+ν₃≈ ν₁+2ν₄, the spectrum of the contact (CF₄)₂ dimer is identified. Agreement between this spectrum and the calculated spectrum is achieved by simultaneously taking intramolecular and intermolecular resonances into account. The distance R _C-C in the dimer is 4.85(15) Å. The calculations of the spectra of (¹²CF₄)₂ and (¹³CF₄?¹²CF₄) dimers with this value of R _C-C in the region ν ₃≈2ν₄ agree with the experiment.     

High-resolution spectroscopy of the 16-μm bending fundamental of CF4

The 16-μm bending fundamentals (ν₄) of ¹²CF₄, ¹³CF₄, and ¹⁴CF₄ have been observed at Doppler-limited resolution using a tunable PbSnSe semiconductor diode laser. The tetrahedral splittings of the rotational manifolds have been observed in all three branches, and in particular the dense and partially overlapping transitions in the Q branches have been resolved and assigned. A least-squares fit of the Hamiltonian, including off-diagonal terms, yielded five scalar and three tensor spectroscopic constants for each of the three isotopes. From these constants the upper-state rotational constant B₄ and the Coriolis constant ζ₄ have been calculated, together with some of the other molecular constants. An absorption feature at about 0.18 cm^?1 to the red of the main Q branch of each isotopic species has been identified as the Q branch of (ν₂ + ν₄) ? ν₂, which is the transition that lases when CF₄ is pumped by a CO₂ laser at 9.4 μm (i.e., in ν₂ + ν₄).     

Electron spectroscopy with excited atoms and photons.: X. Halogen-substituted methanes and methyl amines

Electron binding energy spectra have been measured for CH₃Cl, CH₃Br, CH₃I, CFCl₃, CF₂Cl₂, CF₃Cl, CF₄, CH₃NH₂, (CH₃)₂ NH and (CH₃)₃N. Measurements have been made using 584 Å (21.22 eV) photons as well as with 2³S(19.82 eV) and 2¹S(20.62 eV) metastable helium atoms. Relative spectral intensities are compared for photoionization and Penning ionization.     

Multi-dimensional 1H NMR nuclear Overhauser spectroscopy under magic angle spinning: theory and application to elastomers

The process of cross-relaxation between different protons (nuclear Overhauser effect) is investigated in soft solids by 2- and 3-dimensional NMR under the conditions of fast magic-angle spinning. The cross-relaxation rates are found to depend weakly on fast motions in the Larmor frequency range and strongly on slow motions of the order of the spinning frequency W _R. Explicit expressions for the W _R dependent cross-relaxation rates are derived for different motional models. These findings were tested experimentally on elastomers, i.e., on a cross-linking series of styrene-butadiene rubbers where the cross-relaxation was studied as a function of W _R. Short mixing times as are required for extracting the relaxation rates could be realized conveniently using a pulsed magnetic-field gradient for coherence pathway selection. As in solution NMR, relative couplings between chemically resolved spins can be determined from the peak intensities. By combining cross-relaxation measurements with T ₁ measurements, the distribution of correlation times can be probed for slow and fast timescales, respectively. Only the former were found to depend on the crosslink density.     

Supersonic free-jet quantum cascade laser measurements of ν4 for CF3Cl and CF3Cl and FTS measurements from 400 to 1260 cm

A supersonic free-jet spectrum of the ν₄ band of CF₃Cl has been measured using a quantum cascade laser system. Those measurements were combined with a low temperature (−67 °C) FTS spectrum of the region 1060-1260 cm⁻¹ and with room temperature FTS measurements down to 400 cm⁻¹ to give improved values for the rovibrational constants for the ν₁, ν₂, ν₃, 2ν₃, 2ν₅, ν₄, and ν₅ states of CF₃³⁵Cl and CF₃³⁷Cl. The principal perturbation found by earlier investigators in the ν₁ band is treated as a very weak Coriolis interaction at several avoided crossings of the rotational levels of the ν₁ state and the 2ν₅ state with kl < 0. None of the other vibrational states showed any signs of perturbations. With these new measurements we now have high resolution data on all of the fundamental vibrational states except ν₆.     

The ν4 fundamental of three isotopic species of CF4

The vibration-rotation spectra of the ν₄ fundamental of ¹²CF₄, ¹³CF₄, and ¹⁴CF₄ have been observed with 0.06 cm^?1 resolution. A least squares fit of the data has been used to evaluate the pertinent molecular constants. The band centers are 631.199, 629.285, and 627.348 cm^?1 for ¹²CF₄, ¹³CF₄, and ¹⁴CF₄, respectively. The Coriolis constant ζ₄ has been estimated for the three isotopes.     

Ultraviolet laser-induced fluorescence spectrum of fluorochlorocarbene in solid argon

CFCl has been produced for spectral investigation by matrix reactions of alkali metal atomic beams with CFCl₃ in argon followed by rapid quenching to 15°K on a tilted copper wedge. When these samples were irradiated with near uv light from a krypton ion laser, a very intense, highly structured fluorescence spectrum was observed. This emission system extended from about 25 000 cm^?1 to 15 000 cm^?1 and peaked in intensity at about 22 000 cm^?1. The three most intense progressions are assigned to transitions from a common excited state to ground state levels (0v₂0), (1v₂0) and (1v₂1). New molecular constants determined from these progressions include $\text{ω}{}_2{}^0\text{= 446}\text{cm}{}^{\mathrm{?1}}$, x₂₂ = ?1.2 cm^?1, x₁₂ = ?3 cm^?1, x₂₃ = ?4 cm^?1, and x₁₃ = ?6 cm^?1. CFCl was also produced by in situ photolysis of CFCl₃ using laser plasma emission and by alkali metal atom reactions with CF₂Cl₂, CF₂ClBr, and CHFCl₂.     

The frequency,fluence and pressure dependence of the absorption of pulsed CO2-laser radiation by CF2HCl

Absorption measurements in the CF₂HCl fundamental vibrational band v₃, and combination band v₅ + v₉, for laser energy fluence between 0.1–1.2 cm⁻² and 1–100 Torr gas pressure, are reported. Three distinct regions are experimentally observed for the fluence dependence of the absorption cross section σ and the average number of absorbed photons <n>. Adding Ar buffer gas to CF₂HCl enhances the absorption efficiency only in the v₃ band.     

Enhancement of the electrochemical properties with the effect of alkali metal systems on PEO/PVdF-HFP complex polymer electrolytes

Polymer blend electrolytes based on poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) were prepared by using different lithium salts LiX (X = ClO₄, BF₄, CF₃SO₃, and N [CF₃SO₂]₂) using solution casting technique. To confirm the structure and complexation of the electrolyte films, the prepared electrolytes were subjected to X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. Alternating current (AC) impedance analysis was performed for all the electrolyte samples at various temperatures from 303 to 343 K. The result suggests that among the various lithium salts, LiN[CF₃SO₂]₂-based electrolytes exhibited the highest ionic conductivity at 8.20 × 10^?4 S/cm. The linear variation of the ionic conductivity of the polymer electrolytes with increasing temperature suggests the Arrhenius-type thermally activated process. Activation energies were found to decrease when doping with lithium imide salt. The dielectric behavior has been analyzed using dielectric permittivity (ε*), electric modulus (M*), and dissipation factor (tanδ) of the samples. Cyclic voltammetry has been performed for the electrolyte films to study their cyclability and reversibility. Thermogravimetric and differential thermal analysis (TG/DTA) was used to ascertain the thermal stability of the electrolytes, and the porous nature of the electrolytes was identified using scanning electron microscopy via ion hopping conduction. Surface morphology of the sample having maximum conductivity was studied by an atomic force microscope (AFM).     

Infrared spectroscopic study of the reaction of H atoms with CF2 in argon and nitrogen matrices

The concurrent generation of CF₂ and of H atoms upon exposure of samples containing CF₂N₂ and either HI or H₂S isolated in an argon or a nitrogen matrix at 14 K to 2537-Å mercury-arc radiation leads to the appearance of prominent infrared absorptions of HCF₂, demonstrating that this species is the primary product of the H + CF₂ reaction. Infrared absorptions assigned to HCF₂, DCF₂, CF₂I, and CF₂S in previous studies on other reaction systems are confirmed in the experimental studies here reported.     

Infrared spectrum and molecular force field of CF2Cl2

The infrared spectrum of CF₂Cl₂ has been measured under medium resolution in the range 1600-400 cm^?1. More than 100 bands including fundamental, overtone, combination, and “hot” bands of the three isotopic species CF₂³⁵Cl₂, CF₂³⁵Cl³⁷Cl, and CF₂³⁷Cl₂ have been identified. The band contour studies have enabled the fundamental vibrations to be unambiguously assigned, including the modes ν₃ and ν₇, the positions of which were previously in doubt. The observed values for CF₂³⁵Cl₂ in conjunction with the frequency shift data for CF₂³⁵Cl³⁷Cl and CF₂³⁷Cl₂ have been used in determining a general valence force field, which adequately describes the system investigated. A Fermi resonance interaction between ν₈ and ν₃ + ν₉ levels for the three isotopic species has been interpreted. The corresponding perturbations between those levels obtained by adding ν₂ or ν₅ to both ν₈ and ν₃ + ν₉ have also been found and the related features carefully investigated.     

Double resonance spectroscopy of freon 12: Hot bands of CF235Cl2 and CF235Cl37Cl and the ν6 fundamental of CF237Cl2

Computer-assisted analysis of hundreds of double resonance signals from CF₂Cl₂ has yielded constants for the hot bands ν₆ + ν₄ − ν₄ of CF₂³⁵Cl₂ and CF₂³⁵Cl³⁷Cl and ν₆ + ν₅ − ν₅ of CF₂³⁵Cl₂. It has also produced the first experimental data over the ν₆ fundamental of CF₂³⁷Cl₂.     

IR Laser Control of the Clustering of CF<Subscript>3</Subscript>Br Molecules during the Gas-Dynamic Expansion of a CF<Subscript>3</Subscript>Br/Ar Mixture: Bromine Isotope Selectivity

The infrared (IR) laser radiation control of the clustering of CF3Br molecules during the gas-dynamic expansion of a CF₃Br/Ar mixture at the exit from a nozzle is investigated. Prominence is given to studying the possibility of bromine-isotope-selective suppression of the clustering of CF₃Br molecules due to their resonance vibrational excitation in the gas-dynamic expansion zone near the nozzle. A continuous CO₂ laser is used in experiments to excite molecules and clusters in a beam, and a quadrupole mass spectrometer is used to detect them. The experimental setup and the experimental technique are described. The dependences of the efficiency of molecule clustering suppression on the exciting laser radiation parameters, the gas parameters (composition, pressure) above the nozzle, and the distance from the nozzle exit section to a molecule irradiation zone are obtained. Bromine-isotope-selective suppression of molecule clustering is shown to occur at the exit from the nozzle due to the resonance vibrational excitation of gas-dynamically cooled CF₃Br molecules. When CF₃Br/Ar mixtures are used at pressure ratios p(CF₃Br): p(Ar) = 1: 10 and 1: 30, the enrichment of a cluster beam by bromine isotopes are K_enr(⁸¹Br) ≈ 1.18 ± 0.09 and 1.12 ± 0.07 during the 9R(30) laser line (1084.635 cm^–1) irradiation of a jet. The clustering suppression selectivity is α ≈ 1.18 when the mixture at the pressure ratio p(CF₃Br): p(Ar) = 1: 10 is used. These results suggest that the proposed method can selectively control the clustering of the molecules containing the heavy element isotopes that have a small isotope shift in IR absorption spectra (OsO₄, WF₆, UF₆).     

Specific features of the inhibition of the combustion of propane-air and hydrogen-air mixtures by trifluoromethane and pentafluoroethane

Experimental data on the flammability limits and combustion kinetics of propane-air mixtures at atmospheric pressure in the presence and absence of CF₃H, C₂F₅H, CF₄, N₂, and CO₂ additives are presented. It was found that CF₃H and C₂F₅H inhibit the process of combustion. At the same time, the effect of CF₄, N₂, and CO₂ is caused only by mixture dilution, with a marked contribution of heat capacity in the case of CF₄ and CO₂. The mechanisms of chain termination by the inhibitors and the reasons for their different efficiency in the inhibition of hydrogen and propane combustion are explained.     

Short-wavelength luminescence in Ho-doped KGd(WO4)2 crystals

Emissions from the high-lying excited states, energy transfer and upconversion processes are investigated in Ho³⁺-activated KGd(WO₄)₂ crystal. The spectral assignment based on time-resolved emission spectra allowed to identify various near ultra-violet (UV), blue and green emissions starting from the excited ³H₅, ⁵G₄, ⁵G₅, ⁵F₃ and ⁵S₂ levels. The temporal behavior of these transitions after pulsed excitation was analyzed as a function of temperature and holmium ions concentration. The shortening and nonexponentiality of the decays, observed with increasing activator concentrations, indicated cross-relaxation (CR) among the Ho³⁺ ions. Cross-relaxation rates were experimentally determined as a function of activator concentration and used to evaluate the values of the nearest-neighbor trapping rates X₀₁ and to model the decays. It was observed that KGW, despite higher than in YAG maximum phonon energy of about 900 cm⁻¹, is more efficient short-wavelength emitter than YAG. Examples of the excited-state absorption (ESA) and energy transfer (ET) mechanisms responsible for the upconverted, short-wavelength emissions were identified by analyzing fluorescence dynamics and possible energy resonances.     

Pressure broadening and collisional shift of the Rb D2 absorption line by CH4, C2H6, C3H8, n-C4H10, and He

The pressure broadening and shift rates of the rubidium D2 absorption line 5²S_1/2→5²P_3/2 (780.24 nm) with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He were measured for pressures ≤80 Torr using high-resolution laser spectroscopy. The broadening rates γ_B for CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He are 28.0, 28.1, 30.5, 31.3, and 20.3 (MHz/Torr), respectively. The corresponding shift rates γ_S are −8.4, −8.8, −9.7, −10.0, and 0.39 (MHz/Torr), respectively. The measured rates of Rb for the hydrocarbon buffer gas series of this study are also compared to the theoretically calculated rates of a purely attractive van der Waals difference potential. Good agreement is found to exist between measured and theoretical rates.     

TEA CO2 laser-induced photodissociation of UF6 via interspecies V-V energy transfer from multiple photon excited halomethanes

The dissociation of UF₆ sensitized by multiple photon excitation of a series of halomethanes: CF₄, CF₃Cl, and CF₂Cl₂ has been investigated. The roles of various experimental parameters like exciting frequency, fluence and pressures of sensitizer/UF₆ on the dissociation yield were studied to examine (1) the characteristics of the sensitizer/UF₆ system and (2) the coupling of vibrational energy between two molecular systems. The efficiency of the energy transfer process was estimated on the basis of long range dipole-dipole interaction to gain an understanding of the dissociation process.