摘要:

In this paper we shall be concerned with the energetics of selective ionization processes in simple nonpolar fluids and with the nature of electron localization in polar fluids, studied over a wide density range. The static features of bound Wannier states and of the conduction band in simple solid and fluid insulators were monitored by vacuum-ultraviolet absorption spectroscopy and photoemission studies providing quantitative information concerning the energy of the bottom of the conduction band, impurity ionization potentials, and adiabatic polarization energies. Electron localization in subcritical and supercritical water and ammonia was studied by pulse radiolysis methods. A critical, temperature dependent, density ρCfor electron localization in ND3was observed. The weak density dependence of the maximum of the absorption band of the localized electron in D2O and ND3, and the temperature and density dependence of ρCin ND3, provide compelling evidence for the crucial role of density fluctuations on electron localization in polar fluids.

ISSN:0008-4042    

DOI:10.1139/v77-253

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v77-254

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The temperature dependence of the TMPD photoionization energy threshold,I, in a set of eight hydrocarbon solvents has been systematically studied, from room temperature down to 77 K. For this purpose ion-pair formation is detected either by measuring the photocurrents in the liquid phase or by measuring the recombination luminescence intensity in the solid phase. It is found thatI(liquid) increases linearly when the temperature is decreased down to the liquid–solid transition temperature. At this temperatureIundergoes an abrupt increase of 0.2–0.6 eV depending on the hydrocarbon and the nature of the phase transition. Any subsequent solid–solid phase change is accompanied by a new shift towards higher energy. In the low temperature phase of all the studied crystals,I(solid) has a constant value down to 77 K. Glass-forming liquids have a very different behavior:Ivaries linearly in the liquid and the straight line extrapolates to theI(glass) value at 77 K. The applicability of the two methods is discussed. From the present data it is concluded that the conduction state energy,V0, is constant in the low-temperature phase of crystals. By calculating the polarization energy due to the TMPD+cation and from data on the temperature dependence ofV0in the liquid phase, we have estimatedV0in crystallinen-hexane (0.64 eV) and 2,2,4-trimethylpentane (0.44 eV) and in the plastic phase of cyclohexane (0.47 eV) and 2,2-dimethylbutane (0.01 eV). Finally a correlation ofIwith the medium density is described.

ISSN:0008-4042    

DOI:10.1139/v77-255

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

According to various authors, the value of the yield of the solvated electron in the pulse radiolysis of hexamethylphosphorotriamide (HMPT) varies from 1.2 to 2.4 and increases to 4.2 or 3.1 in the presence of NaBr. We exposed this compound to γ rays after purification and saturation with N2O. N2was formed with a yieldG(N2) = 4.4 ± 0.4. After elimination of a certain number of processes which might also lead to N2formation, it was concluded that thisG(N2) corresponds to the total yield of electrons. This value was confirmed by measuringG(Br−) obtained by radiolysis of HMPT withp-bromophenol as a scavenger. The yield of N2remains constant whenever solutes generally known as good electron scavengers are added (H+, CH3COCH3, NO3−). An interpretation of the results leads to the suggestion of the formation of a dielectron in this medium.

ISSN:0008-4042    

DOI:10.1139/v77-256

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v77-257

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The amounts of ionization produced by absorption of X radiation in the liquids xenon, krypton, and argon are respectively 1.5, 1.4, and 1.2 times greater than those produced by the absorption of the same energy in the corresponding low density gases. The yields of free ions in the irradiated liquids were measured at applied electric fields 1–40 kV/cm and extrapolated to infinite field strength. The total number of ionizations per 100 eV absorbed wasGtot = 6.6 in xenon, 6.0 in krypton, and 4.5 in argon. The reason that the ionization yield is larger in the liquid than in the corresponding low density gas is partly that the energy gapEgbetween the top of the valence band and the bottom of the conduction band in the liquid is smaller than the gas phase ionization potential IP. The ratio IP/Eg = 1.36 for xenon (Roberts and Wilson), 1.27 for krypton, and 1.17 for argon (from data of Jortneret al.). An extra source of ionization in the liquid might be reaction of the higher excited states, M* + M → [M2+ + e−].

ISSN:0008-4042    

DOI:10.1139/v77-258

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The theory of the processes by which subexcitation electrons lose energy in molecular liquids is considered. It is convenient to classify such losses as resulting from 'indirect' and 'direct' interactions; the former interactions arise from the transient electric field of the electron and the latter from the short range quantum mechanical forces occurring in direct collisions. Indirect processes are considered at some length; Monte Carlo trajectories for electrons are generated and the Fourier spectrum of the electric displacement obtained from which energy loss to dipolar relaxation and infrared-active vibrations are estimated. A tight binding scheme is used to derive an expression for the rate of energy loss to single-phonon excitation in direct collisions; the same theoretical framework is used to discuss electron trapping by the molecules of the liquid. Finally, some attempt is made to relate the loss mechanisms considered to experimentally known facts. It is concluded that the 'direct' processes are probably dominant and that knowledge of elastic scattering is of primary importance for the construction of a satisfactory theory.

ISSN:0008-4042    

DOI:10.1139/v77-259

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Conduction state energiesV0were measured for liquid neon, argon, krypton, xenon, liquid nitrogen, liquid methane and ethane, and mixtures of methane and ethane by means of photo-effect on a metal electrode. A lower limit ofV0for liquid hydrogen was estimated. From the dependence of the photocurrent on the electric field strength electron penetration ranges could be deduced.

ISSN:0008-4042    

DOI:10.1139/v77-260

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

It is known that the free ion yield is small in irradiated aromatic hydrocarbon liquids. This study uses pulse radiolysis to observe anions of aromatic solutes in matrices at 77 K. In aliphatic matrices, trapped electrons tunnel to aromatic solutes and the anion yield is observed to grow with time. If the concentration of aromatic solute is large (0.1 M) or if the matrix is aromatic, ion recombination via tunneling dominates the anion kinetics, and long lived triplet states are observed to grow in. These results and the effects of other charge scavengers indicate that just a few percent of added aromatic material can dramatically increase the probability of charge recombination in aliphatic media, and that this effect involves decreased charge separation distances. The same effect apparently also occurs in alkane liquids at room temperature.

ISSN:0008-4042    

DOI:10.1139/v77-261

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Experimental evidence for the existence of a Ramsauer–Townsend minimum in the electron scattering cross section for liquid CH4and liquid Ar (Kr and Xe) is presented and discussed. On the basis of evidence obtained from three sources: (i) comparisons of thermal electron mobilities in gases with those in liquids, (ii) changes in the electron mobility with gas density at high and very high gas pressures, and (iii) the dependence of the electron mobility on temperature for liquids whoseV0, the energy of the electron state in the liquid, is ≤0 eV, it is concluded that a Ramsauer–Townsend minimum is exhibited by the electron scattering cross section for CH4, Ar (Kr and Xe) at all densities from a dilute gas to the liquid and that this minimum is shifted to lower energies (closer to thermal) with increasing density.Additionally, it has been found that a Ramsauer–Townsend-type behavior is exhibited by gaseous ethane (C2H6) and propane (C3H8) with the cross section minimum located at lower energies than for methane (CH4). For these latter molecules the measured mean scattering cross sections at thermal energies are comparable with the geometric cross sections.

ISSN:0008-4042    

DOI:10.1139/v77-262

出版商:NRC Research Press    

年代:1977

数据来源: NRC