GIGANTIC HYDROGEN-ION DISCHARGE CURRENTS INITIATED BY A SUBPICOSECONDLASER

The discovery is made of gigantic pulsed currents of the hydrogen-ion discharge at a mercury electrode illuminated by subpicosecond pulses o f a laser radiation. The discharge current I-d, like the laser thermoe mission current I-p, exponentially depends on the intensity L of the l aser radiation, increasing approximately 15-fold in the interval 5.9 t o 12 GW cm(-2). However, as opposed to I-p, the discharge current depe nds linearly on the hydrogen-ion concentration and obeys the slow-disc harge equation with the transfer coefficient a that decreases from 0.1 8 to 0.13 in this interval of L. At the equilibrium H-ads/H+ potential of -0.94 V (NHE), the discharge current is equal to 10(5) A cm(-2) at L = 10 GW cm(-2). The length of the gigantic current pulses is equal to 3 ps. The above characteristics of I-d are in good agreement with t hose expected for a picosecond electrode reaction (PER) of the electro n-proton transfer under the conditions of a nonequilibrium heating of the electron gas to the temperature T-e much greater than T. The trans fer coefficient alpha is equal to T/T-e. The values of a measured at d ifferent L are in good agreement with T-e calculated in terms of the m odel describing the heating of a gas of free electrons. At k(B)T(e) ex ceeding the proton oscillation frequency in the final state, the motio n along the reaction coordinate becomes classical, which leads to an a dditional increase in the PER current. By comparing the PER current an d that of an ordinary discharge, the Frank-Condon factor and the reorg anization energy along the proton coordinate are found. The values of these quantities agree with the results of a semiempirical quantum-che mical calculation of the potential energy surface for the reaction com plex (Hg)(4)(-)-H3O+ reversible arrow (Hg)(4)-H-H2O).