Molecular beam diagnostics with internal state selection: Velocity distribution and dimer formation in a supersonic Na/Na2 beam

The velocity distribution parallel and perpendicular to the molecular beam axis has been determined for molecules in well defined quantum states using TOF — via optical pumping and the Doppler-shift method. It has been found that the flow velocity as well as the speed ratio changes with the internal energy of the molecule. The flow velocity increases with increasing internal energy at low pd values (p is the pressure in the oven, d is the nozzle diameter) while the opposite is true at high pd values. The parallel speed ratio is smaller for molecules in vibrationally excited states and the perpendicular velocity distribution shows excessive tails that are more pronounced for molecules in higher lying levels. The population of individual levels has been monitored via laser induced fluorescence. It does not change monotonically with pd. The population distribution is not in thermal equilibrium and can only be approximately described by a temperature of T_υ, ≈ 150 K. On the basis of these results a simple model for the influence of the recombination of atoms on the expansion is derived: Molecules are initially neither formed in the υ = 0 vibrational level nor with high internal excitation but probably with ? 1000 cm^?1 of internal energy. The recombination leads to fast atoms and molecules. It is the incomplete deceleration of these fast particles together with an efficient quenching process for the internal energy that determines the flow velocity of molecules in individual quantum states at low pd values. At high pd values the acceleration of molecules with much internal energy is incomplete because those molecules have necessarily made only few collisions.     

Molar Volumes and Heat Capacities of Electrolytes and Ions in Nonaqueous Solvents: 1. Formamide

Apparent molar volumes and heat capacities of 27 electrolytes have been measured as a function of concentration in formamide at 25°C using a series-connected flow densimeter and Picker calorimeter system. These data were extrapolated to infinite dilution using the appropriate Debye–Hückel limiting slopes to give the corresponding standard partial molar quantities. Ionic volumes and heat capacities at infinite dilution were obtained by an appropriate assumption based on the reference electrolyte Ph₄PBPh₄ (TPTB). The ionic volumes, but not the heat capacities, agree reasonably well with previously published statistically based predictions. The values obtained are discussed in terms of simple models of electrolyte solution behavior and a number of interesting features are noted, including, possible dependencies of ionic volumes on solvent isothermal compressibility and of ionic heat capacities on solvent electron acceptor abilities.     

An investigation of the lead(II)-hydroxide system

A detailed investigation of the Pb(II)/OH(-) system has been made in NaClO(4) media at 25 degrees C. Combined UV-vis spectrophotometric-potentiometric titrations at [Pb(II)](T) < or = 10 microM using a long path length cell detected only four mononuclear hydroxide complexes. The values of log beta(1)(q)(), for the equilibria Pb(2+)(aq) + qH(2)O <--> Pb(OH)(q)()((2)(-)(q)()()+)(aq) + qH(+)(aq), were -7.2, -16.1, -26.5, and -38.0 for q = 1-4, respectively, at ionic strength I = 1 M (NaClO(4)). Similar results were obtained at I = 5 M (NaClO(4)). No evidence was found for higher order complexes (q > 4) even at very high [OH(-)]/[Pb(II)] ratios, nor for polynuclear species at [Pb(II)](T) < or = 10 microM. Measurements using (207)Pb-NMR and Raman spectroscopies and differential pulse polarography (DPP) provided only semiquantitative confirmation. The mononuclear Pb(OH)(q)()((2)(-)(q)()()+)(aq) complexes are the only hydrolyzed species likely to be significant under typical environmental and biological conditions.     

Acidity constant of hydrofluoric acid

A detailed experimental investigation of the association (acidity) constant of hydrofluoric acid has been made at 25°C in sodium perchlorate media at ionic strengths between 0.01 and 0.5M. Results were obtained by potentiometry using a fluoride ion-selective electrode in conjunction with three types of reference electrode, all involving cells with liquid junction. After careful consideration of possible errors in the present results and a critical study of the literature, a zero ionic strength pK _a ^o (HF) value of 3.18±0.02 is recommended until existing contradictions can be resolved.     

Ion solvation in lithium battery electrolyte solutions. 1. Apparent molar volumes

Apparent molar volumes, V(MX), of seven electrolytes (NaClO₄, NaCF₃SO₃, NaBPh₄, LiClO₄, LiAsF₆, Ph₄AsCF₃SO₃ and KCF₃SO₃) have been determined by vibrating-tube densimetry in nonaqueous solvent mixtures of propylene carbonate (PC) with acetonitrile (AN), dimethoxyethane (DME) and tetrahydrofuran (THF). V(MX) was measured at an electrolyte concentration of 0.05M over the entire solvent composition range wherever possible. Ionic apparent molar volumes of transfer, _tV(ion), were obtained via the tetraphenylarsonium tetraphenylborate (TATB) assumption. _tV(ion) from PC to the mixed solvents are generally strongly negative for both cations and anions consistent with the greater compressibilities and lower dielectric constants of the cosolvents. In PC/AN mixtures cations and anions have similar values of _tV(ion) but in PC/DME and PC/THF mixtures they differ considerably. Cationic volumes show the expected dependence on ion-size but the differences among the anion volumes are much greater than expected at high cosolvent compositions. These effects are discussed in terms of preferential solvation and other solvent interactions. The implications of these findings for lithium batteries are briefly discussed.     

The ionic product of water in highly concentrated sodium perchlorate solutions

The ionic product of water, pK(w)=-log[H(+)][OH(-)], has been determined in aqueous solutions of sodium perchlorate over the concentration range of 1.0-8.0 M at 25 degrees C from high-precision potentiometric titrations carried out in cells with liquid junction using both glass and hydrogen electrodes. The glass electrode results are systematically lower probably as a result of interference by Na(+) ions.     

Potentiometric Investigation of the Weak Association of Sodium and Carbonate Ions at 25°C

The weak association between sodium and carbonate ions has been investigated at 25°C using high-precision sodium ion-selective electrode potentiometry in solutions of ionic strength ranging from 0.5 to 7.0 M in CsCl and in 1.0 M Me₄NCl media. The protonation constants of CO ₃ ^2- (aq) were also measured, using a H⁺-responsive glass electrode in 1.0 M Me₄NCl and NaCl. The value of the ion-pair association constant calculated from the difference in the protonation constants in these two media was in excellent agreement with that obtained from the Na⁺ISE measurements. Evidence is also presented for the formation of extremely weak ion pairs between Na⁺ and HCO ₃ ^- and between Cs⁺ and CO ₃ ^2- .     

The solvation of fluoride ions. I. Free energies for transfer from water to aqueous alcohol and acetonitrile mixtures

The solubilities of NaF and LiF have been measured in mixtures of water with methanol, ethanol, ethylene glycol and acetonitrile over the whole composition range. Gibbs free energies of transfer of the fluoride ion from water to the mixed and pure solvents have been calculated from the solubility data via the tetraphenylarsonium tetraphenylborate assumption. The values so obtained indicate that the fluoride ion is preferentially solvated by water as a result of its strong hydrogen-bonding capabilities. Desolvation of the fluoride ion is especially marked in acetonitrile-rich solutions.     

On the Pressure and Electric Field Dependencies of the Relative Permittivity of Liquids

The dependencies of the relative permittivity of over 50 liquids on the pressure P, as , and of some 40 liquids on the (square of the) electric field E at ambient conditions, as were obtained from literature data. The function was fitted to a simple expression in and the compressibility, _T. These data were used to obtain the limiting slope for the partial molar volumes and the electrostriction of electrolytes in various solvents.     

Scandium sulfate complexation in aqueous solution by dielectric relaxation spectroscopy

Ion association in aqueous solutions of scandium sulfate has been investigated at 25 degrees C and at concentrations from 0.01 to 0.8 M by broadband dielectric spectroscopy over the frequency range 0.2 相似文献