CHARGE-TRANSFER IN HYPERTHERMAL ENERGY COLLISIONS OF LI-METAL-COVEREDCU(001) .2. DYNAMICS OF EXCITED-STATE FORMATION( WITH ALKALI)

We have measured the relative probability of excited state [Li-0(2p)] formation versus the work-function change induced by alkali-metal adso rbates when hyperthermal energy Li+ ions are incident on alkali-metal- covered Cu(001). This probability is broadly peaked as the work functi on phi decreases, and decreases by approximately an order of magnitude when the velocity of the ions in the incident beam is decreased from 1.05x10(5) to 0.52x10(5) m s(-1), and the incident angle is theta(i)=6 5 degrees as measured from the surface normal. Theoretical calculation s based on a many-body solution to the time-dependent Anderson-Newns m odel of char transfer (discussed in the preceding paper) qualitatively reproduce the observed trends. These calcula tions suggest that the p eak in the excited-state probability results mainly from two effects: first, the decreasing difference between the energy of the Li-0(2p) st ate and the Fermi level as the work function decreases, which tends to increase the excited-state probability; and second, the competition o f the Li-0(2p state with the Li-(2s(2)) negative ion state at low work functions, which tends to decrease the excited-state probability. Dif ferences between the Li-0(2s) and Li-0(2p) lifetimes also play a role in the formation of the peak, as does electron-hole pair production.