SUBPICOSECOND-PULSE-LASER-INDUCED ELECTRON-EMISSION FROM MERCURY AND SILVER INTO AQUEOUS-ELECTROLYTES

Highly efficient superlinear electron emission from liquid mercury and polycrystalline silver electrodes into aqueous electrolyte solutions has been discovered. The effect is induced by visible subpicosecond-la ser pulses (300 fs) with a photon energy (hv approximate to 2 eV; 615 nm) less than the threshold of the linear photoeffect. The charge dens ity q emitted from mercury by 615-nm laser pulses increased from 10(-9 ) to 10(-5) C cm(-2) in the intensity range I=4-30 GW cm(-2). At silve r, 10(-9) to 10(-7) C cm(-2) were generated in the range of I=7-70 GW cm(-2). The charge density grew with the concentration of electron acc epters (H3O+ and CHCl3) at I<20 GW cm(-2), because the capture of emit ted electrons prevents them from returning to electrode surface. The s ubsequent slow electron reduction of the electron capture products (H- atoms and CHCl2-radicals, respectively) indicates the laser-induced el ectron transfer across the interface. Ultraviolet 300-fs-pulses (hv ap proximate to 4eV) at intensities I<6 GW cm(-2) lead to effective quant um yields corresponding to one-photon emission. This emission disappea red at Hg when 6-ps-pulses were applied with the same energy but still occurred at Ag. These results conform with theoretical predictions of charge-intensity dependencies, pulse duration and electrode potential characteristics for thermoelectron emission of a nonequilibrium elect ron gas from metals into electrolyte solutions.