Determination of photoelectron emission threshold in liquid methylamine: conduction band concept for electron-accepting energy states in polar solvents

Abstract

Threshold potentials were measured for photoelectron emission from Pt, W, and Hg electrodes into liquid methylamine containing BuCl, BuBr, and N{sub 2}O as electron scavengers. From these values determined photoelectrochemically, the lowest unoccupied energy level (V{sub O}) of liquid methylamine at -50{degree}C was found to be -0.61 {plus minus} 0.03 eV relative to vacuum, which was 0.7 eV more positive than that of liquid ammonia at -55{degree}C, -1.29 eV. The V{sub O} value in either of the solvents was more positive than the solvation energy of a solvated electron in the corresponding solvent by 0.65 eV for methylamine and by less than 0.29 eV for ammonia. The unambiguous difference in the energetic separation between ammonia and methylamine (0.29 and 0.65 eV) and similar kinetic parameters of solvated electron electrodes in both solvents favored the conduction band model over the preexisting solvent trap model to account for the meaning of V{sub O} values evaluated from the photoelectron emission experiments.