Showing papers in "The Journal of Physical Chemistry in 1976"

Correlation of photocurrent-voltage curves with flat-band potential for stable photoelectrodes for the photoelectrolysis of water

Abstract: Using the differential capacitance technique, the flat-band potential of n-type TiO2, SnO2, SrTiO3, KTaO3, and KTa(077)Nb(023)O3 electrodes has been determined as a function of pH in aqueous electrolytes Plots of flat-band potential vs pH are linear in all cases and have a slope of approximately 0059 V/pH unit The flat-band potential correlates nicely with the onset for photoanodic currents corresponding to O2 evolution at the n-type semiconductor and H2 at the dark Pt cathode The ordering of flat-band potentials at a given pH is SrTiO3 of the order of KTaO3 of the order of KTa(077)Nb(023)O3 greater than TiO2 greater than SnO2 (SnO2 most positive vs a saturated calomel electrode)

Yield and decay of the hydrated electron from 100 ps to 3 ns

Abstract: Energy is deposited by fast electrons in water in small localized volumes called spurs. The decay of the hydrated electron in a spur has been measured to be about 17 percent between 100 ps and 3 ns. Half of this decay occurs before 700 ps where previous techniques could not observe any decay. The principal reactions of the hydrated electron in the spur are presumed to be e/sup -//sub aq/ + e/sup -//sub aq/, e/sup -//sub aq/ + H/sup +/, and e/sup -//sub aq/ + OH. Scavengers for the hydrogen ion are about equally effective in slowing the decay as are scavengers for the hydroxyl radical except for OH/sup -/ which seems unusually effective. This suggests H/sup +/ and OH are distributed similarly with respect to e/sup -//sub aq/. Spur decay is also observed for the products of electron capture, Cd/sup +/ or RSSR/sup -/, where RSSR is cystamine. The observations reconcile different methods for measurement of the initial hydrated electron yield to 4.6 +- 0.2 molecules/100 eV, and combined with our earlier data, provide the major features of the history of e/sup -//sub aq/ in the spur from 100 ps to the achievement of a homogeneous distribution.

An Equilibrium and Kinetic Investigation of Salt-Cycloamylose Complexes

Abstract: : The equilibrium constants and rate constants for the formation of inclusion complexes of cycloheptaamylose with small inorganic anions were measured by a spectrophotometric technique and an ultrasonic relaxation technique respectively. The stability of the complexes of anions with cycloheptaamylose decreased. Comparison is made between the equilibrium constants and the interaction of free anions with the solvent. Periodate and ClO4(-) exhibited a complexation rate constant 30 times greater than the remainder of the anions. A concentration independent relaxation was observed for aqueous cyclohexaamylose in the uncomplexed state. No like behaviour was observed for cycloheptaamylose. A conformational change in the cycloheptaamylose may be the rate determining step in the complexation of the more slowly reacting anions.

Quenching of the luminescence of the tris(2,2'-bipyridine) complexes of ruthenium(II) and osmium(II). Kinetic considerations and photogalvanic effects

Abstract: The quenching of the charge-transfer excited states of Ru(bpy)/sub 3//sup 2 +/ and Os(bpy)/sub 3//sup 2 +/ by O/sub 2/, Fe/sup 3 +/, Co(phen)/sub 3//sup 3 +/, Ry(NH/sub 3/)/sub 6//sup 3 +/, Os(bpy)/sub 3//sup 3 +/, and Fe(CN)/sub 6//sup 3 +/ has been studied by a spectrofluorometric method. The lifetime of the emitting state of the osmium (II) complex and the rate of its reaction with Ru(NH/sub 3/)/sub 6//sup 3 +/ were measured by a single-photon counting technique. A value of -0.96 V was estimated for the reduction potential of the Os(bpy)/sub 3//sup 3 +/ parallel *Os(bpy)/sub 3//sup 2 +/ couple. Emission intensity measurements were used to determine the steady-state concentrations of the Fe/sup 2 +/ and Ru(bpy)/sub 3//sup 3 +/ formed in the reaction of Fe/sup 3 +/ with the emitting state of Ru(bpy)/sub 3//sup 2 +/. The steady-state concentrations of the electron-transfer products increase in the order HCl < H/sub 2/SO/sub 4/ < HClO/sub 4/ approx. CF/sub 3/SO/sub 3/H and in 0.5 M HClO/sub 4/ amount to about 25 percent of the initial Ru(bpy)/sub 3//sup 2 +/ concentration under the conditions used. The Ru(bpy)/sub 3//sup 2 +/-Fe/sup 3 +/ system exhibits a large photogalvanic effect. The mechanisms ofmore » the reactions are discussed and general equations describing the steady-state characteristics of these systems are derived. (auth)« less

Effect of an electric field on electron attachment to sulfur hexafluoride, nitrous oxide, and molecular oxygen in liquid argon and xenon

Abstract: The rate constant for electron attachment to SF/sub 6/, N/sub 2/O, and O/sub 2/ in liquid argon and xenon was studied as a function of an external electric field up to 10/sup 5/ V cm/sup -1/ While k(e/sup -/ + SF/sub 6/) and k(e/sup -/ + O/sub 2/) decreased with increasing field strength, k(e/sup -/ + N/sub 2/O) exhibited a nearly 100-fold increase The field effect on the rate constant in the liquefied rare gases is related to the increase of the mean electron energy by the external field By means of the Cohen--Lekner theory electron energy distribution functions were obtained and a rough estimate of the energy dependence of the attachment cross section could be deduced

Vibrational constants and force field of sulfur hexafluoride

Abstract: The infrared-active combination bands of SF/sub 6/ gas were remeasured and the band origins estimated. These data were combined with the Raman frequencies of Bosworth et al., and with the spectrum of SF/sub 6/ in cryogenic liquid oxygen solutions reported by Bertsev et al., to obtain estimates for the 21 anharmonicity constants X/sub ij/. The resulting harmonic vibrational frequencies were used in a calculation of the general quadratic harmonic force field of SF/sub 6/. The most useful constraint in the F/sub 1//sub u/ symmetry block was the Coriolis constant zeta/sub 3/ = 0.693 +- 0.004 obtained from an analysis of ..nu../sub 3/ resolved with tunable diode lasers; but zeta/sub 4/ estimated from a similar analysis of ..nu../sub 4/, and the /sup 32/S--/sup 34/S isotope frequency shifts reported by Brunet and Perez for these fundamentals, are all in general agreement. The more important valence force constants are f/sub r/ = 5.45 +- 0.03, f/sub rr/(cis interaction) = 0.36 +- 0.01, f/sub rr'/ (trans interaction) = -0.02 +- 0.03, and f/sub ..cap alpha../ approximately 0.83, all in mdyn/A. From the absolute band intensities of Schatz and Hornig and the present force field, the S--F bond moment and its derivative are estimated tomore » be ..mu../sub 0/ = 2.44 +- 0.12 D and delta ..mu../delta r = 4.2 +- 0.3 D/A.« less