H2+, H3+ and H− emission by MeV ion impact: charge state dependence of energy and angular distributions

Abstract

A 1MeV/n127Iq+ beam of the Tandem accelerator at Orsay, France, has been used to study the dependence of hydrogen ion emission on the charge state of the incident primary ions. The samples investigated were bare gold and carbon foils and a 150 nm glycine film vacuum-evaporated on an Au foil. The measurements were performed at a vacuum pressure of about 10−7 mbar; the sample surfaces were covered by a contamination layer. The linear time-of-flight instrument used was equipped with two acceleration grids and a position sensitive stop detector, in order to measure the initial velocity components and the angle of emission for each detected ion. The results were axial, radial and total energy distributions and angular distributions for the hydrogen ions H+, H2+, H3+ and axial energy distributions for H−, all measured at constant beam energy for the charge states 17+, 20+, 26+, 30+ or 32+ under an angle of incidence of 55° against the surface normal.The angular distributions of all ions were asymmetric relative to the surface normal, for the glycine target more than for the bare metals. The mean energies increase slightly with the charge state, the increase was in the order of 0.5–2% per charge state. The change of the mean emission angle had negative as well as positive values in the order of 0–0.2° per charge state. Comparing glycine and metal targets, the angular distributions obtained with the metals seemed to be wider around the main direction of emission. A few suggestions about possible desorption/ionization processes are given.