Vibrational relaxation induced population inversions in laser pumped polyatomic molecules

Conditions for population inversion in laser pumped polyatomic molecules are described. For systems which exhibit metastable vibrational population distributions [slow vibration—translation/rotation (V—T/R) relaxation], large, long lived inversions are possible even when the vibrational modes are strongly coupled by rapid collisional vibration—vibration (V—V) energy transfer. Overtone states of a hot mode are found to invert with respect to fundamental levels of a cold mode even at V—V steady state. Inversion persists for a V—T/R relaxation time. A gain of 4 m^?1 for the 2v₃ → v₂ transition in CH₃F (λ ≈ 15.9 μ) was found assuming a spontaneous emission lifetime of 10 s for this transition. General equations are derived which can be used to determine the magnitude of population inversion in any laser pumped, vibrationally metastable, polyatomic molecule. A discussion of factors controlling the population maxima of different vibrational states in optically pumped, V—V equilibrated metastable polyatomics is also given.     

A three-parameter cubic equation of state for asymmetric mixture density calculations

A new three-parameter cubic equation of state of the van der Waals type with one parameter temperature dependent, P = RT/(V − b) − a(T)/[V(V + c) + b(3V + c)], has been developed for representation of liquid volumes (or densities) for asymmetric mixtures such as CO₂C₁₉ and C₁C₁₀. The calculated results are better than those obtained from the two-parameter Peng—Robinson equation, the three parameter Schmidt—Wenzel equation, the volume-translated Soave—Redlich—Kwong equation proposed by Peneloux et al., and the volume-translated Peng—Robinson equation developed in this work. The parameters of the new equation have been generalized in terms of the acentric factor ω and reduced temperature T_r.     

Vibrational deactivation of DF

Rate constants for deactivation of DF in vibrational states n = 1 to 7 in collisions with DF (0) are calculated semiclassically in the temperature range from 300 K to 3000 K. The variation with the temperature agrees quite well with experiments for n = 1, although the theoretical rates are 30% lower than the experimental values for temperatures above 1200 K and 75% lower at 300 K. This difference is discussed. Single quantum transitions dominate. At 300 K the mechanism is predominantly a V—V transfer for n = 2 and a V-T/R transfer for n = 7, while both mechanisms contribute for n = 3–6. Collision complexes are important for both V—V and V-T/R energy transfer. Rotational relaxation times are calculated for HF and DF.     

Vibrational relaxation of ozone by para and normal hydrogen

The relaxation of O₃(001) by p- and n-H₂ was measured over the temperature range 167–424 K. n-H₂ quenched ozone more efficiently, with the difference between rate constants increasing with temperature. These observations are explained by a near-resonant V—R process, in agreement with the Sharma—Brau theory.     

Solvent—Solute interaction. Solvation of vanadyl acetyl-acetonate in non-aqueous media

The electronic absorption spectrum of vanadyl acetylacetonate has been studied in 15 organic solvents. It has been found that wavenumbers and molar absorptivities of the long-wavelength bands (d-d transitions) can be well described by a complementaryLewis acid—base model includingGutmann's donor number [Gutmann V., Wychera E., Inorg. Nucl. Chem. Letters2, 257 (1966)] and acceptor number [Mayer U., Gutmann V., Gerger W., Monatsh. Chem.106, 1235 (1975)] of a solvent. This model describes also the solvent effect of the hyperfine splitting constant,A _iso (⁵¹V), from e.s.r. spectra of VOacac ₂. These observations are discussed in terms of the donor—acceptor concept for solvent—solute interactions.     

Vapour pressure of binary,three-phase (S-L-V) systems and solubility

Solubilities and vapour pressures along the solid-liquid equilibrium line for systems 2-t-butyl-4-methylphenol+benzene, 2-t-butyl-4-methylphenol+cyclohexane, 2,6-di-t-butyl-4-methylphenol+benzene, 2,6-di-t-butyl-4-methylphenol+cyclohexane and enthalpies of fusion for six phenols have been measured.The effect of specific interactions, leading to association, on solubilities and vapour pressures of 13 binary three-phase systems (S—L—V) has been discussed. Results of solubility prediction from vapour pressure measurements and vice versa are presented.     

Investigation of the cardiotoxic peptides of the venom of the cobraNaja oxiana

Six populations of basic polypeptides have been found in the venom of the Central Asian cobraNaja oxiana Eichwald, and four of them — V″c-1, V″c-2, V″c-5, and V″c-6 — have been obtained in the electrophoretically homogeneous state. On a perfused frog heart preparation, all the basic polypeptides proved to be cardiotoxic. However, only some of them (V′c-2, V″c-3, and V″c-4) were characterized by arrhythmic activity as well as by the negative ino- and chronotropic effects, common for all of them. An enhancement of the specific cardiotoxic effect of each of the polypeptides by pure phospholipase A-2 has been shown.     

Étude des réactions d'oxydo—réduction du neptunium dans le mélange Rbcl—CsCl (25–75% mol)

The oxidation—reduction reactions o f neptunium in molten RbCl—CsCl.Standard potentials of the systems NpO₂(VI)—NpO₂(V) and Np(IV)—Np(III) and the equilibrium constant of the following disproportionation reaction 2NP⁴⁺ + 2H₂O + 2Cl^- ? NpO⁺₂ + Np³⁺+ 4HCI have been determined in a (Rb 0,25; Cs 0,75 )C1 melt in the temperature range 660—750°C by absorption spectrophotometry. The results are com- pared with those obtained previously in (Li 0,7; K 0,3)C1, (Li, K)C1 eutectic and (Li 0,55; CsO,45)Cl.     

Rotation-vibration-translation energy transfer in laser excited Li2 (B1Πu)

Using the method of laser fluorescence, inelastic collisions with rare gas atoms of electronically excited ⁷Li₂ molecules in the υ = 2 and 4 levels were studied. Vibrational transitions ranging from Δ = +2 to ?4 were observed. The simultaneous rotational transitions were completely resolved, and detailed rate constants k_{Δυ, ΔJ} for specific collision- induced quantum jumps Δυ, ΔJ were determined. The effect of secondary rotational relaxation was eliminated by an extrapolation to zero pressure. By integration over ΔJ, rate constants k_Δυ, were found. They are, within the error limits, independent of the collision partner and on the initial υ (2 or 4) and depend rather weakly on Δυ. These findings are compared with theoretical results from various methods, generally based on a collinear collision model. The apparent disagreement in all respects suggests strongly the importance of rotational degrees of freedom in the collision. Experimental evidence for this is the large amount of V — R transfer observed, which about equals the V — T transfer. The mean cross sections σ(Δυ) for specific vibrational transitions Δυ range between 6 and 15 A², among the largest ever observed.     

Polarography of some sulphur-containing compounds : Part XII.Anodic waves of dialkyldithiocarbamates

Dialkyldithiocarbamates give only a one-electron anodic wave. The various adsorption phenomena are probably caused by varying orientation of the mercury compounds on the electrode surface; the irregular i-t curves recorded at —0.04 V and the anomalous behaviour of the anodic current between +0.2 V and —0.4 V can be interpreted as the behaviour of an adsorbed film at the electrode. Analytical measurements are best made in 60% ethanolic 0.1 M sodium hydroxide media at concentrations of about 10^-5 M dialkyldithiocarbamate; a method is given for the analysis of the monoalkyl and dialkyl compounds in mixtures.     

Polarographic determination of semicarbazones

Acetone, methyl isobutyl ketone, acetaldehyde, formaldehyde, cyclohexanone, butyraldehyde, crotonaldehyde, and acrolein semicarbazones all give polarographic waves suitable for quantitative analysis in an acetate buffer at pH 4.6 .The half-wave potentials are —1.3, —1.3, —1.16 —1.05, —1.2,—1.11, —1.06,–0.99 V vs. S.C.E., respectively, for the compounds listed above. The diffusion current constants of these compounds average approximately 7 in the concentration range of 10^-2 to 10^-1 mM, giving an extremely sensitive method of carbonyl compound analysis. A supporting electrolyte that is 0.1M each in acetic acid, sodium acetate, sodium chloride, and semicarbazide, and 0.0016% in Triton X-100, is satisfactory both for polarograph analysis and for the quantitative absorption of acetone, acetaldehyde, cyclohexanone, and crotonaldehyde from air samples by means of a scrubber.     

Coulometric determination of chromium

This paper describes an accurate and precise method for the determination of chromium by coulometry at controlled potential. A solution of the sample in 6M hydrochloric acid is electrolyzed at a large stirred mercury cathode whose potential is maintained constant at —1.10 V vs. S.C.E. ;this reduces the chromium quantitatively to the +2 state. Copper, lead, and a number of other elements are next eliminated by simply discarding the mercury and replacing it with fresh mercury ;then uranium is re-oxidized to non-interfering uranium(IV) by a second controlled-potential electrolysis at —0.80 V vs. S.C.E.; and finally the solution is electrolyzed at a working electrode potential of —0.40 V vs. S.C.E. This serves to re-oxidize the chromium quantitatively to the +3 state, and the analysis consists of measuring the quantity of electricity consumed in this oxidation.Of the elements commonly associated with chromium, only vanadium (and, when it is present in large amounts, molybdenum) interfere in this procedure.     

Binuclear cationic μ-bromo complexes of vanadium(II)

The compounds [V₂(μ-Br)₃L₆]BPh₄, with L = 3-methyltetrahydrofuran (1) and tetrahydrofuran (2), have been prepared. The crystal and molecular structures of 1 have been determined. The compound crystallizes in space group Cc with unit cell dimensions a = 18.499(3), b = 10.923(3), c = 29.619(7) Å, β = 103.18(2)^o, V = 5827(5) ų and Z = 4. The [V₂(μ-Br)₃(CH₃C₄H₇O)₆]⁺ ion is analogous to the [V₂(μ-Cl)₃L₆]⁺ cations previously described, but has a longer V—V distance, viz. 3.146(4) A. The UV-vis spectrum shows a double spin-flip transition but it is extremely weak compared to that in the chloro analog. Qualitatively, this was expected because of the ca 0.16 Å increase in the V—V distance, but the magnitude of the decrease (∼ 5 fold) is of interest.     

Spectroscopy and energy distribution study of the Cl + HI chemical laser

The spectral distribution of the pulsed, flash initiated Cl + HI → HCl(ν) + I chemical laser (3.6μ–4.0μ) was studied in both free running and grating selected systems. New transitions in both cavities are reported. The relative populations of the lasing HCl vibrational levels were measured using the grating selection technique. The relative distributions were found to be N₃/N₂ = 1.10 to 1.29 and N₂/N₁ = 2.23 to 2.32. A computational comparison between the chemical laser results and previous measurements by the infrared chemiluminescence method is made in view of vibrational V—R,T,V′ relaxation processes which may change the nascent population distribution.     

Ethyleneglycol-bis(aminoethyl)tetraacetic acid in the amperometric titration of cadmium in the presence of zinc

Cadmium can be titrated amperometrically with EGTA in the presence of zinc; three modifications of the titration are described. The diffusion current of cadmium may be used to follow the titration at —0.90 or —0.70 V vs, the S.C.E, in ammoniacal or acetate-buffered medium respectively The titration may also be performed in ammoniacal solution at —0.30 V vs. the S.C.E., using copper as the amperometric indicator. The influence of iron, aluminium, magnesium, alkaline earths and lead was studied. Ascorbic acid could be used to mask iron and as an effective remover of oxygen. Under appropriate conditions cadmium could be titrated in the presence of 500-fold amounts of zinc. The titration error is approximately 0.002–0.003 ml of a 0.1 M titrant solution.     

Level-to-level vibrational energy transfer studies: energy dependence and observation of product species for azulenes(S0, Evib) + CO2

V—V energy transfer from a large molecule excited to vibrational energies of chemical interest has been demonstrated by detection of ≈ 1.5% yield of CO₂(001) due to energy transfer from azulene (E_vib ≈ 30600 cm^?1. Also, the average enery lost per collision by azulene was measured as a function of E_vib, and the rate constant for CO₂(001) deactivation by azulene was determined.     

Reagentless lactate sensor based on cytochrome b2

The sensor is based on cytochrome b2 adsorbed on the semi-conducting N-methyl-phenazinium—7, 7,8,8-tetracyanoquinodimethane complex held on a platinum electrode. At an applied potential of —0.03–0.4 V (vs. Ag/AgCl), steady-state currents are reached in 0.5–0.7 min. The optimal pH is 6.6. Lactate in the range 10^-5 –lO^-3 M can be determined. The sensor is useful for 3–9 days depending on the enzyme source.     

Equation of state calculations for CO2, C2H4 and N2 using perturbation theory. Effect of damping the quadrupole—quadrupole and induced-quadrupole series at small intermolecular separations

Mohan, R., Prahlada Rao, D. and Babu, S.V., 1986. Equation of state calculations for CO₂, C₂H₄ and N₂ using perturbation theory. Effect of damping the quadrupole—quadrupole and induced-quadrupole series at small intermolecular separations. Fluid Phase Equilibria, 25: 171-193.Pure component equation of state (EOS) and thermodynamic property calculations are made for three quadrupolar molecues CO₂, C₂H₄ and N₂. A simple ‘spherical + quadrupole—quadrupole (Q—Q) + induced-quadrupole (ind-Q)' potential model is assumed to represent the molecular interaction. However, the usual Q—Q and ind-Q interaction energy series expansion expressions are retained only beyond a chosen intermolecular separation, r_cut-off, close to the molecular size. For smaller separations, the diverging nature of the series is damped in an extreme manner by putting these interaction energies to zero. Perturbation theory and an optimisation procedure are used to calculate the reduced thermodynamic quantities, the optimal values of the parameters, σ, ε, and finally the saturation loci, pressure, entropy, internal energy at high densities for the real systems. A comparison with experimental data indicates the usefulness of considering damped multipole—multipole, induced-multipole interactions in high pressure studies.     

A laser induced fluorescence study of vibrational energy transfer in dideuteromethane

V—V and V—T/R rates of ν₁, ν₂, ν₃, ν₆, ν₈, and ν₉ of CH₂D₂ were measured and are reported. The deactivation efficiencies of rare gas collision partners were measured and calculated by SSH theory, the results are reported and discussed. Possible V—V pathways are presented and discussed.     

Burnett—isochoric P—V—T measurements of a nominal 20 mol% hydrogen—80 mol% methane mixture at elevated temperatures and pressures

A new apparatus is described which has been developed to measure P—V—T relations for hydrogen—hdyrocarbon systems at elevated temperatures and pressures. The principal components are three heavy-walled spherical pressure cells with the same outer/internal diameter ratio, a fully submerged differential pressure cell, and measuring equipment including calibrated piston guages and a platinum resistance thermometer. This apparatus was used to measure densities of a 20.05±0.05 mol% hydrogen?79.95±0.05 mol% methane mixture from 273.15 to 600 K and pressures to 72 MPa. Two Burnett isotherms at 273.15 K established fluid densities without direct measurement of either mass or volume. Eight isochores, ranging in density from 1.62 to 14.91 mol dm^?3, were anchored to the Burnett isotherms at 273.15 K where their densities were firmly established. An analytic equation for the thermodynamic surface has been fitted to the resulting P—V—T data, giving a 0.01% root mean square deviation of calculated compressibility factors from experimental results.