Conduction level and thermalization range parameter of electrons in liquid alkanes

The conduction level V₀ in some linear, cyclic and branched alkanes is measured by the difference between metal/vacuum and metal/liquid work functions. Aging of photocathodes has an effect on the work function values and on the V₀(zinc) values, but not on V₀(gold). This difference of behavior is suggested to be due to the structure of the metal/liquid interface, a charge oxide layer for zinc, an adsorbed layer for gold. The results for gold are n-hexane 0.02 eV, n-pentane 0.01 eV, cyclopentane -0.04 eV, cyclohexane -0.17 eV, 2-2-4 trimethylpentane -0.25 eV, and 2-2 dimethylbutane -0.30 eV, and are comparable to Holroyd´s data. The thermalization range parameter B of photoelectrons is determined by fitting the experimental curves I=f(E), photocurrent vs. electric field, with the one-dimensional Onsager escape probability, assuming a Gaussian or an exponential distribution of the thermalized photoelectrons. B zinc values are higher than gold values, but taking the thickness of the oxide layer into account reduces this difference. The fit is better for n-pentane, n-hexane (V₀ positive) and worse for 2-2-4 trimethylpentane and 2-2 dimethylbutane (V₀ negative). B values are very reproducible, for each liquid and metal. They are lower than those resulting from volume injection processes, e.g. for a gold photocathode and a Gaussian distribution: n-hexane 3.55 nm, n-pentane 4.1 nm, cyclohexane 3.65 nm, cyclopentane 4.55 nm, 2-2-4 trimethylpentane 7 nm, and 2-2 dimethylbutane 7.9 nm.