Photoemission of n-ethylene glycols in the vacuum ultraviolet

Measurements of the absolute photoemission of liquids in the vacuum ultraviolet (UV) have been taken. Studies have focused on photoelectric yields of diethylene glycol, triethylene glycol, and tetraethylene glycol undoped and doped with lithium hydroxide solution (LiOH). The electron mean free paths calculated from experimental photoyields are submitted. Photon fluxes are determined by filling the ion chambers with argon gas. The absolute photoyield curves generally show monotonic behavior with the values in the neighborhood of 15% to 20%. These absolute photoyields are higher than expected. The data of our experiments indicate that the effects of doping with alkali salts on these n-ethylene glycols are small.

Two papers (Nemec, 1975; Casanovas, 1981) on photoemission into vacuum give the photoelectric threshold energy to be about 8.0 eV for 11 organic liquids. Our experimental data give other values. The relation between the photoyields and the electron mean free paths is broken down in the photon energy region 16 eV to 30 eV when the threshold energy is 8 eV. It is suggested therefore that the photo electric threshold energy be less than 8 eV and larger than 7 eV.

Our electron mean free paths were compared with the empirical equation predicted from Seah and Dench (1978) for organics. The electron mean free paths calculated from our experimental data exceeded those predicted by Seah and Dench. Therefore the empirical equation is not suitable for these n-ethylene glycols in the photon energy region 16 eV to 30 eV at low pressure.