J. P. Guelfucci

Photoconductivity studies in some nonpolar liquids

Measurements of the photoconductivity of liquid n‐pentane, n‐hexane, cyclopentane, cyclohexane, neopentane, neohexane, and tetramethylsilane induced by far UV radiation (7⩽hν⩽10 eV) have been performed. We have studied the influence of the incident photon energy, of the applied electric field strength, and of the concentration of two electron scavengers (carbon tetrachloride and perfluoromethylcyclohexane). Our results show that in going from the gas phase to the liquid phase, the ionization energy threshold values of these low dielectric constant liquids are lowered by about 1.6 eV. The introduction of an electron scavenger reduces drastically the solvent photocurrent. Our results are consistent with the quenching, by the scavenger, of a solvent expanded excited state, precursor of the geminate ion pair, and not with an epithermal electron scavenging as in high energy photon irradiation.

Photoconductivity of liquid 2, 2-dimethylbutane and liquid 2, 2, 4-trimethylpentane

Abstract The photoconductivity dependence on photon wavelength has been studied between 120 and 170 nm for liquid 2,2-dimethylbutane and for liquid 2,2,4-trimethylpentane. The values of the liquid phase photoionization energy threshold for these two alkanes are respectively: 8.49±0.05 eV and 8.38±0.05 eV .

Determination of the ionization quantum yield and thermalization distance of photoelectrons created by v.u.v. photoionization in pure liquid alkanes and tetramethylsilane

Abstract The photocurrents, in liquid n -hexane, n -pentane, cyclohexane, cyclopentane, 2-2-4 trimethylpentane, 2-2 dimethylbutane, neopentane and tetramethylsilane, produced by v.u.v. irradiation, are measured at electric fields from 2 to 35 kV cm -1 . Assuming the one- and three-dimensional Onsager probabilities are respected, the values of the attenuation parameter of the photon flow B 1 , the quantum yield for the production of an ion-pair θ i , and the attenuation parameter of the photoelectron flow B 3 can be deduced. These values are compared with those provided by other injection methods. Both the validity of these values and the theoretical models are discussed. The discussion is extended to other parameters: V 0 , μ 0 and K J , all correlated to emission and propagation mechanisms in non-polar liquids.

Application of the semi-empirical method to determine the spatial distribution function for thermalized photoelectrons created by vacuum ultraviolet or high-energy irradiation of some nonpolar dielectric liquids

A semi-empirical method is tested to determine the spatial distribution function of the thermalized photoelectrons, created by vacuum ultraviolet (VUV) or γ irradiations of some liquid alkanes. It seems that modified exponentials must be associated to the thermalization process on VUV irradiation. A Gaussian distribution function could be used for high-energy irradiation. The partial inadequacy of the method in the case of high-energy irradiation can be imputed to the existence of multiple ion pair recombinations.

Photoionization of a 50 cSt viscosity polydimethylsiloxane silicone oil

We have studied the influence of incident photon energy (6⩽hv⩽10 eV) and of applied electric field strength (0 < E ⩽ 15 kVcm-1) on the photoconductivity of Rhone-Poulenc 604 V 50 silicone fluid. Its photoionization energy threshold value is: 7.29±0.05 eV. Within the studied electric field range we observed a strong influence of the field on the shape of the I = f(hv) curves.

Ion Mobility Measurements in a 50 cSt Viscosity Polydimethylsiloxane Silicone Oil

Using two different time-of-flight techniques (pulse voltage and V.U.V. photons pulse) ion mobility measurements have been performed, at room temperature, on a purified and direct 50 cSt polydimethylsiloxane silicone oil (Rhône Poulenc 604 V 50). These experiments have been carried out in a cell with plane parallel electrodes, for electric fields strengths ranging from 0.4 kV cm⁻¹ to 8 kV cm⁻¹ and for three electrode gaps(0.1 cm, 0.15 cm and 0.27 cm). The effect of some additives like N<inf>2</inf>O and C<inf>7</inf>F<inf>14</inf> has also been investigated. The positive ion mobilities (≅ 6.2 10⁻⁵ cm²V⁻¹s⁻¹) are independent of the additives while, the negative ion mobilities decrease from 6.8 10⁻⁵ cm²V⁻¹s⁻¹ under N<inf>2</inf> to 2.4 10⁻⁵ cm²V⁻¹s⁻¹ in presence of C<inf>7</inf>F<inf>14</inf>.

Thermalization range distributions for photoelectrons injected into dielectric liquids

A photocurrent can be produced by direct illumination of a dielectric liquid with photons having energies in the vacuum ultraviolet (VUV). The kinetic energy initially imparted to an electron by absorption of a photon is subsequently dissipated through random collisions with molecules in the liquid. With the parent cation at the origin, the distance, r, traveled by the electron in coming into thermodynamic equilibrium with the liquid is called the thermalization range. Electron energy thermalization range distribution functions were determined for electrons created by photoionization of cyclohexane, 2,2-dimethylbutane, tetramethylsilane, and two polydimethylsiloxane oils. Except for cyclohexane, the function [r2/2(B3)3]exp(−r/B3), where B3 is an energy-dependent range parameter, gave the best agreement between the calculated and experimental photocurrents at all photon energies considered. Using a Monte Carlo simulation (Goulet type) to represent the slowing down of the electrons after their injection int...