Mobility of excess electrons in liquid hydrocarbon mixtures

. 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 (...

Section: Free Ioit Yiells Aitd Peizetratioit Ranges C?jsupporting

confidence: 70%

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

“…5, are respectively 4-fold and 7-fold smaller than those reported earlier (8). Technical difficulties with the background currents decreased the accuracy of the earlier measurements and prevented the determination of the temperature coefficients of the mobilities (8).…”

Section: Thermal Electron Mobilitiesmentioning

confidence: 72%

Epithermal Electron Ranges and Thermal Electron Mobilities in Liquid Aromatic Hydrocarbons

Shinsaka¹,

Freeman²

1974

Radiolysis free ion yields were measured as functions of electric field strength and temperature in benzene, toluene, 1,2-, 1,3-, and 1,4-dimethylbenzene, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene, 1,2,3,4- and 1,2,4,5-tetramethylbenzene, pentamethylbenzene, hexamethylbenzene, naphthalene, and anthracene. Secondary electron ranges bGP were estimated from the yields. The density-normalized ranges bGPd were almost constant, 34−38 × 10−8 g/cm2, from benzene up to the tetramethylbenzenes, then increased to 47 × 10−8 in pentamethyl- and 52 × 10−8 in hexamethylbenzene. In naphthalene and anthracene the normalized ranges were 32 and ∼20 × 10−8 g/cm2, respectively. Electron mobilities in the liquids at 293 K, and their activation energies, expressed in (cm2/V s, kcal/mol) were: benzene (0.114, 7.4); toluene (0.063, 3.4); 1,2-dimethylbenzene (0.018, 4.4); 1,3-dimethylbenzene (0.057, 4.5); 1,4-dimethylbenzene (0.062, —); 1,2,3-trimethylbenzene (0.022, 4.8); 1,2,4-trimethylbenzene (0.035, 4.3); 1,3,5-trimethyl-benzene (0.17, 3.2); 1,2,3,4-tetramethylbenzene (∼0.02, 5). The mobilities reflect migration retarding influences of the aromatic ring and molecular asymmetry, and a slight ring-shielding effect of methyl groups that tends to enhance the mobility.

“…5. Values for n-butane ( 9 , n-pentane (7,8), and n-hexane (6,8,24) are included for comparison. For a given value of bGp the tendency is for u, to increase in the order n-alkane < cycloalkane < cycloalkene < 1,4-cyclohexadiene or benzene.…”

Section: Electron Mobilitiesmentioning

confidence: 99%

Electron Mobilities and Ranges in Liquid Hydrocarbons: Cyclic and Polycyclic, Saturated and Unsaturated Compounds

Shinsaka¹,

Dodelet²,

Freeman³

1975

KYOII SHINSAKA, JEAN-POL DODELET, and GORDON R. FREEMAN. Can. J. Chem. 53,2714 (1975.Penetration ranges bGP of secondary electrons into 21 X-irradiated liquids were estimated from measured free ion yields. The density normalized ranges bcpd are independent of temperature. Increasing the molecular symmetry by creating one or more cycles in the molecule causes the normalized range to increase, provided that the amount of bond distortion due to strain remains small. Ranges are smaller in compounds that contain strained rings. Energy transfer from the secondary electrons to the molecules is enhanced by the presence of distorted bonds in the molecules. The ranges in olefins are affected by the same factors as those in saturated hydrocarbons, with the addition of a contribution of transient negative ion states to the energy transfer processes. Shielding the double bond by methyl groups is not effective; the effect of the added methyl groups on the molecular symmetry is a more important factor. The magnitude of the energy transfer interaction is an inverse function of molecular symmetry.The general correlation between bGp and thermal electron mobilities u. in liquids contains significant variations within it. For a given value of bGp, u, in different liquids increases in the order n-alkane < cycloalkane < cycloalkene < 1,4-cyclohexadiene or benzene. Arrhenius plots of u, in cyclic olefins curve downwards at low temperatures, due to the formation of a deeper trapped state of the electron. The trap is deepest in 1,4-cyclohexadiene (21 kcal/mol) and is attributed to an equilibrium between solvated electrons and anions at temperatures below about280K.KYOJI SHINSAKA, JEAN-POL DODELET et GORDON R. FREEMAN. Can. J. Chem. 53,2714Chem. 53, (1975. Les parcours des electrons secondaires, bGp, ont etk estimes d'aprts les rendements en ions libres mesurks dans 21 liquides irradits aux rayons X. NormalisCs pour la densite, ces parcours, bcpd, deviennent independants de la temperature. Une augmentation de la symktrie molCculaire par cyclisation simple ou multiple entraine une augmentation du parcours normalise, tant que la distorsion des liaisons demeure faible. Un important transfert d'energie des electrons secondaires est realise dans le cas de molCcules a cycle tendu, ce qui reduit le parcours des electrons dans de tels liquides. Les parcours electroniques dans les olefines sont fonction des mCmes facteurs que dans les alcanes, avec en plus la possibilite d'un transfert d'energie via la tendance a former un ion negatif CphCmere. L'addition de groupes mtthyles ne protege pas une double liaison, mais affecte la symetrie moleculaire. L'importance de la quantite d'energie transferee par collision est une fonction inverse de la symktrie moltculaire. La correlation gknerale entre bGP et la mobilitC de I'electron thermique dans les liquides presente une structure fine. Pour une valeur de bGp donnte, u. augmente selon I'ordre suivant: n-alcane < cycloalcane < cycloalctne < cyclohexaditne-1,4 ou benzene. La courbe obtenue en portant u, s...