Temperature dependence of vibrational energy transfer in liquids: VV relaxation of CO(ν = 1) by O2 in liquid Ar from 86 to 145 K

The rate constant for the energy transfer process

has been measured for CO and O₂ dilute in liquid Ar along the coexistence curve between 86 and 145 K. The results are compared to gas phase measurements of this rate constant over the same temperature range. The ratio of the rate constants in the two phases is compared to that predicted by an application of the isolated binary collision (IBC) model for energy trasnfer, which scales the energy transfer rate constants by the rate constants for binary collisions in the two phases. The theoretical predictions of the IBC model are that the liquid state energy transfer rate constant, k^ℓ, should be 30–60% greater than the gas phase energy transfer rate constant, k^g. The measured value of k^ℓ is, within the experimental error, equal to that for k^g. Possible reasons for the discrepancy are discussed.     

Kinetic Relationships between Reactions in the Gas Phase and in Solution

Some recent examples of reactions proceeding both in the gas phase and in solution have been investigated to determine their kinetics and mechanisms. The ratio of the corresponding rate constants, k_G and k_L, of the elementary processes studied has been found to be about unity for unimolecular reactions and between 1 and 10 for bimolecular reactions. The mechanisms, overall rates, rate constants, and activation energies have been determined for the homogeneous gas reaction NOCl + Cl₂O = NO₂Cl + Cl₂ and the reaction NOCl + N₂O₅ = NO₂Cl + 2 NO₂, carried out in C₂F₃Cl₃.     

Vibrational energy storage in high pressure mixtures of diatomic molecules

CO/N₂, CO/Ar/O₂, and CO/N₂/O₂ gas mixtures are optically pumped using a continuous wave CO laser. Carbon monoxide molecules absorb the laser radiation and transfer energy to nitrogen and oxygen by vibration–vibration energy exchange. Infrared emission and spontaneous Raman spectroscopy are used for diagnostics of optically pumped gases. The experiments demonstrate that strong vibrational disequilibrium can be sustained in diatomic gas mixtures at pressures up to 1 atm, with only a few Watts laser power available. At these conditions, measured first level vibrational temperatures of diatomic species are in the range T_V=1900–2300 K for N₂, T_V=2600–3800 K for CO, and T_V=2200–2800 K for O₂. The translational–rotational temperature of the gases does not exceed T=700 K. Line-of-sight averaged CO vibrational level populations up to v=40 are inferred from infrared emission spectra. Vibrational level populations of CO (v=0–8), N₂ (v=0–4), and O₂ (v=0–8) near the axis of the focused CO laser beam are inferred from the Raman spectra of these species. The results demonstrate a possibility of sustaining stable nonequilibrium plasmas in atmospheric pressure air seeded with a few percent of carbon monoxide. The obtained experimental data are compared with modeling calculations that incorporate both major processes of molecular energy transfer and diffusion of vibrationally excited species across the spatially nonuniform excitation region, showing reasonably good agreement.     

The direct l-type resonance spectrum of CF3CCH in the vibrational state v10=3: Extension of the theory of reduction to H6n terms

The direct l-type resonance spectrum of CF₃CCH has been measured in the v₁₀=3 vibrational state by means of waveguide microwave Fourier transform spectroscopy in the range 8–26 GHz. Three types of direct l-type resonance transitions induced by the (Δk=Δl=±2) interaction could be observed: 140 transitions following the ΔJ=0, Δk=Δl=±2, Δ|l|=0, selection rule covering values of J=17–61 and G=|k−l| from 1 to 7, 94 transitions following the ΔJ=0, Δk=Δl=±2, Δ|l|=±2, selection rule covering values of J=26–57 and G from 15 to 24, 90 transitions following the ΔJ=0, Δk=Δl=±4 selection rule covering values of J=34–80 and G from 3 to 12 and 13 transitions following the ΔJ=0, Δk=Δl=±6, k=∓1, l=∓1⇔k=±5, l=±3 selection rule for J=71-83. 14 A₁–A₂ splitting transitions with kl=+1 were measured from J=33 to 49. Strong perturbations due to Δ(k−l)=±3 interactions made possible the observation of perturbation-allowed transitions with selection rule k=±4, l=±3⇔k=±3, l=∓1. Furthermore, the rotational transitions J=2–1, 3–2 and 4–3 have been measured. To make use of the multiple fitting concept, the theory of reduction developed for the v_t=2 vibrational state by Sarka and Harder [K. Sarka, H. Harder, J. Mol. Spectrosc. 197 (1999) 254] has been extended to the v_t=3 vibrational state including terms up to H₆₂. Owing to problems in the reproduction of data with low K and A₁–A₂ symmetry, two types of fits have been performed using five reduced forms of the effective Hamiltonian. The first type of fit used a reduced data set for which part of the transitions has been omitted. The unitary equivalence of the determined parameter sets has been demonstrated including newly derived relations for parameters in v₁₀=3. In the second type of fit, the complete data set has been included, yielding satisfactory results only in one reduction. In both type of fits, parameters up to sixth order have been determined including the axial rotational constant A and the Coriolis constant Aζ for both values of l. General features of the direct l-type resonance spectrum in a v_t=3 level are discussed.     

Vibrational energy exchange between CO(v=1) and 14N2 and CO(v=1) and 15N2XXXured to 60 k in the gas phase

Laser fluorescence technique has been used to measure (VV) exchange rates between CO(v = 1) and ¹⁴N₂ and ¹⁵N₂ XXX At 65 K exchange to ₁₅N₂ has 65 times the higher rate constant. Comparison with data for (VV) exchange in liquid ₂ shows that the isolated binary collision theory does not hold for the case of CO(v = 1) and ¹⁴N₂.     

A novel experimental technique for measurement of mass transfer between liquids and gas bubbles in agitated vessels: Application to highly viscous liqu

A novel experimental transient technique for obtaining the volumetric mass transfer coefficient between an agitated liquid and a bubbling gas is propos The method uses a constant volume stirred tank in which a gas is brought into contact with a liquid. The mass transfer coefficient k_La and Henry coefficient are estimated as parameters of a dynamic model of the system from pressure evolution measurements.This method is particularly designed for gas mass transfer measurements in highly viscous fluid. Correlations between k_La, the stirring sha speed, the inlet gas velocity and the power input per unit volume are proposed.     

Vibrational relaxations of NO by atomic oxygen

A laser-induced fluorescence method has been used to study the vibrational relaxation of NO by atomic oxygen, i.e. NO(v=1) + O — NO(v=0) + O(2). The NO was excited indirectly by vibrational-vibrational energy transfer from HCI(v=1), these molecules having been prepared using the output from a pulsed HCl chemical laser. The experiments yield: k₂=(6.5 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1 at (296 ± 3) K.     

Experimental measurement and prediction of hydrate forming conditions in the nitrogen-propane-water system

Experimental data on initial hydrate formation conditions have been obtained for the nitrogen-propane-water system in the L₁HG, L₁L₂H, and L₁L₂HG regions, where L₁ is the water rich liquid phase, L₂ is the hydrocarbon rich liquid phase, H is the hydrate and the G is the vapor phase. The measurements covered a range of temperatures from about 275 to 293 K and pressures from about 0.3 to 17.0 MPa. The concentrations covered for the L₁HG region extended from 0.94 to 75.0 mole percent propane in the gas phase, and for the L₁L₂H region they extended from 83.1 to 99.0 mole percent in the condensed liquid phase. Four-phase measurements were made at concentrations of propane from 18.1 to 71.1 mole percent in the gas phase.The experimental data were used to find a fitted binary interaction parameter for predicting hydrate formation in systems containing nitrogen and propane.     

Ionic solvation in water + co-solvent mixtures. Part 8. Total free energies of transfer and free energies of transfer with the “neutral” component removed of single ions from water into water + acetone

The acid dissociation constants of a wide range of acids in water+acetone mixtures have been combined with values for the free energy of transfer of the proton. ΔG⁰_t(H⁺ to calculate values for the free energy of transfer of ions which derive only from the charge on the ion. ΔG⁰_t(i)_c. As the values of ΔG⁰_t(H⁺) have been revised, revised values for the total free energies of transfer of cations and anions, ΔG⁰_t(M⁺) and ΔG^o_t(X^-), are given. New data for ΔG^o_t(MX_n) is also split into values for ΔG⁰_t(Mⁿ⁺) (where n=1 and 2) and ΔG⁰_t(X^?). These free energies of transfer, both total and those deriving from the charge alone, are compared with similar free energies in other mixtures water+co-solvent. Values for ΔG^o_t(i)_c do not conform to a Born-type relationship and show the importance of structural effects in the solvent even when only the transfer of the charge is involved.     

Excess Gibbs energies of the ternary system ethanol+N,N-dimethylformamide+cyclohexane at 298.15 K

Vapour–liquid equilibrium (VLE) for the ternary system ethanol (EtOH)+N,N-dimethylformamide (DMF)+cyclohexane (Cy) and for the relevant binary mixtures containing DMF have been determined at 298.15 K by headspace gas chromatographic analysis of the vapour phase directly withdrawn from an equilibrium apparatus. Measurements of liquid–liquid equilibria in both binary DMF+Cy and ternary mixtures have been also carried out. The binary VLE data have been described with different correlation equations. The capabilities of different models of either predicting or reproducing the ternary data have been compared. Excess Gibbs energies G^E as well as activity coefficients γ_i of components have been obtained and briefly discussed. While EtOH+DMF behaves almost ideally with slightly negative G^E-values, both EtOH+Cy and DMF+Cy exhibit large positive deviations. The G^Es of the ternary system are positive with the exception of a narrow region in dilute Cy. The excess entropy and the temperature dependence of G^E and γ_i have been calculated in the whole ternary domain from the known excess enthalpy and heat capacity. The predictions by different equations of the effect of temperature on the mutual solubilities of DMF and Cy as well as on the binodal curve of EtOH+DMF+Cy have been compared with experiment.     

Infrared spectral evidence for tricarbonyldinitrosylchromium,Cr(CO)3(NO)2—A re-examination

The evidence for the d⁸ carbonyl—nitrosyl Cr(CO)₃(NO)₂ is re-examined. Making use of ligand effect constants, to calculate energy-factored force constants and ν(CO) frequencies, we conclude that Cr(CO)₃(NO)₂ does not have the D_3h structure suggested by Satija et al. [Inorg. Chem. 17, 1737 (1978)]. We find that it has a C_2v structure, with the NO groups occupying two equatorial positions of a trigonal bipyramid.The hitherto unidentified complex Cr(CO)₄(NO), which was formed in low yield in Satija et al.'s experiments, appears to have a C_4v structure that is very similar to the isoelectronic molecule Mn(CO)₅.     

Microwave Spectrum of 1,3-Dioxolane in the v=4-8 States of Hindered Pseudorotation

The microwave spectrum of 1,3-dioxolane (C₃H₆O₂) (8 GHz - 53 GHz) has been studied. We identified 247 b type transitions in the v=4, 5, 6, 7, 8 states of excited pseudorotation: rotational transition; vibration-rotation transitions between the v=5 and v=6 states and between the v=7 and v=8 states. Rotational constants, centrifugal distortion constants, and coupling constants between general rotation and hindered pseudorotation have been determined. The intervals _{v v'} between the pseudorotational energy levels have been evaluated: ₅₆=298,618 MHz and ₇₈=201,078 MHz.     

Electrode kinetics of the metal complexes with aminopolycarboxylic acids: Part II. Cadmium-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complexes

The d.c. polarographic current-potential curves of Cd(II)-EDTA complexes were examined in the pH range 0.5–10.0, to elucidate the mechanism of their electrode processes and to determine the relevant electrochemical kinetic parameters. It was shown that the first wave observed below pH 3 at ?0.58 to ?0.65 V vs. SCE is the reversible reduction wave of Cd(II) aquo-ion with kinetically-controlled limiting current, and the second wave observed above pH 1.5 at ?0.75 to ?1.21 V vs. SCE corresponds to the simultaneous irreversible reduction of four complex species, CdH₃L⁺, CdH₂L, CdHL^? and CdL^2?, where CdH_pL^(p?2)+ and L^4? denote the protonated complex species with p protons and the unprotonated EDTA ion, respectively. Analysis of the dependence of limiting current on the hydrogen ion concentration led to the conclusion that the preceding reaction determining the behaviour of limiting current is CdH₃L⁺?Cd²⁺+H₃L^? with k₃^d=6.3×10² s^?1 and k₃^f=3.3×10⁶ s^?1M^?1, where k₃^d and k₃^f are the dissociation and formation rate constants, respectively. On the other hand, from analysis of the dependence of half-wave potentials of the second wave on the hydrogen ion concentration, the kinetic parameters of the four complex species were evaluated, and are given in Table 1. Further, it was shown that the cathodic rate constants of these four charge transfer processes at some reference potential together with those of Cd(II)-HEDTA complexes fulfil the linear free energy relationship.     

A flash photolysis study of the elimination of dinitrogen from trans-(N2)2W(dppe)2; dppe = 1,2-bis-diphenylphosphinoethane

Flash photolysis of trans-(N2)2W(dppe)2 (1) at ?60, ?30, ?10°C, and room temperature indicates that loss of dinitrogen occurs stepwise via the following proposed intermediates. Photodissociation of 1 gives the transient A decaying with k1 ～ 4450 s?1 to the doubly coordinatively unsaturated species [W(dppe)2], B. Further reactions of B are dependent on the type of gas used to saturate the solutions. In N2-saturated media, B is efficiently reconverted into the starting complex 1 via (N2)W(dppe)2], C(N2), kN22 = 450 s?1, which in turn takes up a second molecule of N2, kN23 = 3.7 s?1. In CO-saturated solutions, trans-(CO)2W(dppe)2 is produced as the final product and the corresponding rate constants are kCO2 1500 s?1 for B → C(CO) and kCO3 = 1.14 s?1 for C(CO) → product. In Ar-saturated solvents, B is transformed, again in two steps; kAr2 = 1 s?1 and kAr3 = 0.1 s1?, to products of unknown structure.The different rate constants kN22, kCO2, kAr2 and kN23, kCO3 and kAr3, together the common activation energy of ca. 11 kcal/mol?1 for the three processes A → B, B → C(N2) and C(N2) → 1 suggest that the reactions of B and C occur by SN2-type displacement of coordinated solvent molecules by the incoming ligands.     

Kinetics of CN(v=0) and CN(v=1) with H2 HCl and HBr

CN radicals have been generated in their X ²Σ⁺ (v=0) and (v= 1 ) levels by pulsed laser photolysis of NCNO at 532 nm, and time-resolved laser-induced fluorescence has been used to measure the rates of their removal by H₂, HC1 and HBr. The rate constants for removal of CN(v= 1 ) by these three species are 1.2 ± 0.3, 1.1 ± 0.2 and 1.3 ± 0.1 times the rate constants for reaction of CN(v=0). The results can be interpreted in terms of vibrationally adiabatic theory and a CN vibrational frequency which is almost the same in the transition state as in the isolated radical.     

Vapor phase infrared spectrum and coriolis coupling constants of pentacarbonyl(thiocarbonyl)chromium(0)

Several band contours have been successfully resolved in the high-resolution IR spectrum of pentacarbonyl(thiocarbonyl)chromium(0) vapor at ~312 K. However, PQR separations are only clearly discernible for the three v(CO) fundamentals (v₁,v₂ and v₁₆). The good agreement between the observed and calculated PR separations of the two a₁v(CO) modes (v₁ and v₂) verifies the C_4v prolate symmetrical top geometry of the molecule. From band shape analyses, the Coriolis coupling constants of the ev(CO) mode (v₁₆) and the e δ (CrCO) mode (v₁₇) are estimated to be —0.45 ± 0.05 and —0.80 ± 0.15, respectively.     

LIF measurement of the vibrational dependence of the N2(B 3Π g ) hyperfine splitting parameters

From very high resolution (8 MHz FWHM) LIF measurements, the hyperfine coupling constants of N₂(A ³Σ _u ⁺ ) and N₂(B ³Π _g ) have been obtained for three pairs of vibrational quantum numbersv′,v″. TheA-state constants are in very good agreement with accurate literature data. The vibrational dependence of some of theB-state constants is found to be much more pronounced. This is qualitatively explained in terms of the electronic structure of the two states.     

Electrooxdation of Tricarbonyl(N,N-Diphenylcyclohexadienecarboxamide)Iron Complexes. Reversibility of Electron Transfer and Free Energy Change

Qualitative and quantitative criteria of irreversibility of electron transfer in cyclic voltammetry (CV) of tricarbonyl(N,N-diphenylcyclohexadienecarboxamide)iron complexes were investigated. The measurement of the heterogeneous rate constants for electron transfer according to CV data over an extended range of free energy change ( ΔG) for these complexes are described. Kinetic analyses of the electrochemical technique demonstrates that when the applied potential exceeds the standard potential E°, the experimental rate constant k_e represents an accurate measurement of the intrinsic rate constant k₁ for electron transfer. However, as the applied potential is less than E°, the reversibility of the electron-transfer process becomes increasingly more important, and the rate constants for reverse electron transfer k_-t and decomposition k₂ of the electrogenerated intermediate have to be taken into account.     

Preferential energy transfer from N2(A) to specific energy levels of Cu atoms

Emission spectra resulting from reaction of “clean” N₂(A³ Σ_u⁺) with copper atoms were studied using a flowing afterglow apparatus. The population distribution of the Cu states was calculated from the spectrum; it indicates that Cu atoms are excited by nearly resonant energy transfer processes. N₂(A,v') + Cu(²S_{$\text{1}\text{2}$}) → N₂(X, v) + Cu^* , and that the transfer is most efficient for N₂(A,v') → N₂(X,v) transitions with large Franck-Condon factors. The preferential energy transfer results in population inversion between some of the Cu states.     

Intermode vibrational crossing in CH3Br*

Subsequent to Q-switch CO₂-laser pumping of the v₆ band of CH₃Br, rate constants for activation and deactivation of other modes have been measured. v₁, v₄ and v₂, v₅ are populated in about 60 gas kinetic collissions, and v₃ in about 170 collissions. All modes decay at the same rate, corresponding to about 335 collissions. Measurements have also been made on deactivation of the various modes by rare gases. The results are discussed in terms of possible mechanisms and in comparison to those on CH₃F and CH₃Cl. Considerations based on available theories of vibrational relaxation seem to give considerable, though quantitatively imperfect, insight into energy transfer in these species.