Electron Mobilities and Ranges in Liquid Ethers: Ion-like and Conduction Band Mobilities

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The value of the rate constant kl for the reaction e-s,lv + RO-s,lv + H, [I], at 295 K and 1 bar is 51.4 X lo5 s-1 in methanol and 5 8 X 104 s-1 in ethanol. The respective volumes of activation averaged between 1 bar and 2 kbar are AVl* 2 -21 and 5 -22 cm3 mol-1. A high concentration of potassium hydroxide (1 M) or water (5 M) decreases the apparent value of kl somewhat but has little or no effect on the value of AV,". The effect of pressure on the rate constant of e-s,lv + S + product, [2], was also measured for a series of solutes that displays a wide range of reactivity. Experimental values of AV2* depend on the relative contributions of the effects of solvent density on the reactant diffusion rates, the concentrations of the actual reacting species, and the relative energies of the reactant and intermediate states. For reactions whose rates are near the diffusion controlled limit, k2 = 10'0 M-1 s-1 in methanol and ethanol, the values of AV2' are positive and similar to those for the diffusion of simple ions. AV* (e-s,!v diffusion) = 4 cml mol-1 in methanol and 6 cml mol-1 in ethanol. Cadmium chlor~de IS apparently not completely dissociated in alcohols, and k(e-s,lv + CdC12) < k(e-s,lv + CdCl+) < k(e-,,lv + Cd2+). For a series of compounds with lower rate constants there is a correlation between log k2 and AVz*, the latter being negative for very low values of k2. The products of electron capture by benzene, toluene, ethyl acetate, and possibly acetonitrile appear to be stabilized by protonation: e-,,,I,. + S = S-,,lv, 13, -31,; S-s,lv + ROH + SH + ,I,,[4]. The results indicate that the decomposition of e-s,lv in a pure alcohol occurs by protonatlon of the electron site, e-s,lv + ROH -t H + RO-,,,,, 14'1, rather than by electron transfer to an alcohol molecule followed by decomposition of the anion. [Traduit par le journal]

Section: Eflect Of Pressure On K2supporting

confidence: 91%

Reaction rates of electrons in liquid methanol and ethanol: effects of pressure

Bolton¹,

Robinson²,

Freeman³

1976

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“…2u,,,,,, dominates at low temperatures, while at higher temperatures a conduction band or hopping mechanism becomes important. The ion-like process does not contribute appreciably to electron migration in alkanes under conditions studied thus far (29), so only the second mechanism is treated here.…”

Section: Free Ioit Yiells Aitd Peizetratioit Ranges C?jmentioning

confidence: 99%

“…In an ether the distribution of occupied energy states was empirically related to the optical absorption spectrum of the solvated electrons (29). The low energy side of the spectrum has an approximately Gaussian shape, and in diethyl where ~-' /~a -' is a normalization factor.…”

Section: Free Ioit Yiells Aitd Peizetratioit Ranges C?jmentioning

confidence: 99%

Molecular structure effects on electron ranges and mobilities in liquid hydrocarbons: chain branching and olefin conjugation: mobility model

Dodelet¹,

Shinsaka²,

Freeman³

1976

. Can. J. Chem. 54, 744 (1976). The effect of molecular structure on electron behavior in liquids was studied by measuring secondary electron penetration ranges bGP and thermal electron mobilities II, in substituted methanes and ethylenes. The penetration ranges are smaller (energy transfer cross sections are larger) when the alkane molecules are less rigid. It was confirmed that the epithermal electron energy transfer interaction radius in a liquid phase alkane molecule is limited to two C-C bonds in series. This modifies the earlier noted correlation between b, , and the degree of sphericity of the molecules. For example, the density normalized range b,,d in the relatively sphere-like tetraethylmethane (54 X lo-* g/cm2) is more similar to that in the distinctly nonspherical diethylmethane (11-pentane, 43 X g/cm2) than to that in the sphere-like tetramethylmethane (126 X g/cm2). Tetraethylmethane is too large for the entire molecule to interact with an electron in the liquid phase, and the possibility of rotations about the C-C bonds in the ethyl groups makes the molecule less rigid. Electrons sense these relatively sphere-like molecules to be similar to those of a 11-alkane. Connecting tert-butyl groups to olefinic or acetylenic carbons creates sphere-like quasi neopentyl groups which greatly enhance electron ranges in the unsaturated compounds. In conjugated olefins cis-trans effects are largely overshadowed by the general efficiency of these compounds as electron energy sinks. The earlier noted correlation between be, and u, contains fine structure. For a given value of bGP, 11, increases in the order 11-alkane < cyclo or branched alkane < olefin. Electron mobilities are interpreted in terms of a model that contains a Gaussian distribution of solvated electron state energies, a conduction band, and thermally activated transitions between them. The model is a combination of our treatment of electrons in ethers and Schiller's treatment of electrons in hydrocarbons. The percolation model does not provide a sufficiently complete interpretation of electron migration in hydrocarbons.J.-P. DODELET, K. SHINSAKA et G. R . FREEMAN. Can. J. Chem. 54,744 (1976). L'effet de la structure molCculaire sur le comportement des Clectrons en exces dans les liquides a Ct C Ctudie en mesurant, pour differentes substitutions du mithane et de l'Cthylkne, le parcours des Clectrons secondaires, bo, et les mobilitks des Clectrons thermalises, 11,. Lorsque les molkules d'alcanes perdent leur rigiditC, les parcours Clectroniques sont plus courts. La probabilitC de transfert d'knergie par 1'Clectron Cpithermique est donc plus importante. Le rayon d'interaction de ce dernier avec les molkules d'alcanes a CtC confirm6 h deux liens C-C en strie. Ceci modifie la correlation prCcCdente entre bGp et le degrC de sphericit6 des molCcules. Par exemple, le parcours, normalis6 pour la densite, (bGpri = 54 X g/cm2) dans le tetraCthylmCthane resemble plus au parcours Clectronique dans le 11-pentane (43 X g/cm2) qu'i celui dans le tetramtthylmCthane (...

“…12. The mobility-viscosity relationship varies with the structure of the solvent molecules, but is similar for alkanes and ethers (16). Ions in cyclo-solvents have higher mobilities than those in n-alkyl solvents of the same viscosity.…”

Section: Ion Mobilitiesmentioning

confidence: 94%

Electron mobilities in alkanes through the liquid and critical regions

Dodelet¹,

Freeman²

1977

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JEAN-POL DODELET and GORDON R. FREEMAN. Can. J. Chen~. 55.2264 (1977. Three properties of electrons in liquids are governed by scattering at low energies and show similar dependence upon liquid density and molecular shape. They are the mobility, the dependence of the mobility upon electric field strength, and the penetration range of low energy (i 10 eV) electrons. The scattering cross sections of hydrocarbons in the liquid phase (near or below the normal boiling point) are smaller when the molecules are more sphere-like. The degree of sphericity of the n~olecules in the present series decreases in the order 2,2-dimethylpropane (DMPr) > 2,2-dimethylbutane (DMB) 2 cyclopentane (cP) > n-pentane (nP).Electron mobilities in DMPr and DMB measured as functions of the liquid density pass through maxima similar to those observed earlier in argon and xenon. The magnitudes of the maxima decrease in the order Xe > Ar > DMPr > DMB. The maxima occur at densities approximately double the critical density dc. There is a small maximum for electrons in cP, but none for those in nP.The mobilities in the supercritical gases are similar for the four compounds. The Arrhenius temperature coefficients are all 7-10 kcal/mol (0.3-0.4 eV/electron) for temperatures and densities near the critical values. This implies that electrons form localized states in the gases. The extent of localization in supercritical DMPr appears to be greater than that in the normal liquid. The localization is not the critical phenomenon predicted by Lekner.The mobility in liquid DMPr decreases at high electric field strengths. The magnitude of the field dependence changes with the liquid density and passes through a maximum similar to that of the mobility itself. The field dependence in liquid DMB is smaller than that in DMPr, hut it also passes through a maximum at a density about double d,.Equations are given that describe the mobility in nP at all temperatures from the triple point through to the supercritical gas. The electrons reside mainly in localized states over the entire temperature range, but transport occurs mainly in extendcd states to which the electrons are thernlally excited.The penetration range parameter bGP of secondary electrons in these liquids is normalized for comparison by multiplying by the liquid density d. The values of b,,d plotted against d form curves similar in shape to the against rl curves; but the relative variations in bod are much smaller. JEAN-POL DODFLET et G o~~o sR. FRFEMAN. Can. J. Chem. 55. 2264 (19771. La mobiliti des electrons dans un milieu constitue un outil trks sensible pour determiner la diffusion et le transfert d'knergie des Clectrons thermiques dans ce milieu. Les sections efficaces pour la diffusion et le transfert d'energie des hydrocarbures en phase liquide (a proximite et en dessous de la temperature d'ebullition) sont d'autant moindres que la forme des molCcules approche la forme sphkrique. La sphericit6 des molecules dans la presente strie decroit dans I'ordre suivant: le dimethyle-2,2 propane (DMPr) > ...