Fast H2 Research Articles

Energy loss of fast H2+molecules in solids. I

The electronic energy loss of fast H2+ ions in thin solids is investigated. The energy loss is influenced by the correlated propagation of the protons which act coherently on the target electrons through a pure Coulomb potential. This influence increases with increasing velocity and decreasing target thickness. The model proposed does not involve the so called 'wake potential'.

Collisional dissociation of H2+ and H3+ on molecular targets leading to formation of excited hydrogen atoms

Experimental measurements have been made of the cross sections for dissociation of fast (100–700 keV) H2+ and H3+ ions to give fast H atoms in the 3s excited state; targets for this work were O2, CO, CO2, CH4, C2H6, and C3H8. The technique involved quantitative measurement of Balmer-alpha radiation emitted from fast moving fragments of the dissociated projectile. Contributions to the Balmer-alpha emission from the 3p and 3d levels were eliminated by a method that utilizes the different lifetimes of the 3s, 3p, and 3d states. It is observed that cross sections for H(3s) formation by dissociation on the hydrocarbons all exhibit essentially the same variation with impact energy and increase in magnitude with the complexity of the target; similar behavior is exhibited by the O2, CO, and CO2 group of targets. Comparison of the various cross sections suggests that one cannot assign an effective cross-section value to the constituent atoms of the target molecule.

Energy spectrum of protons produced in collisional dissociation of fast H2+ ions

Energy distributions of protons produced in dissociative collisions of H2+ with H2, Ar and Xe have been measured in the forward direction at 10 keV. An experimental method giving the corresponding excess kinetic energy spectrum in the centre-of-mass system of H2+ is briefly discussed. The measured spectra are explained in terms of electronic and vibrational transitions to dissociative states of the H2+ molecular ion. The dissociation cross section by vibrational transitions in the 1sσg state is estimated to be, respectively, σv = 1.4 × 10-18 cm2, σv = 4.3 × 10-18 cm2 and σv = 5 × 10-18 cm2 for hydrogen, argon and xenon targets. The dependence upon the target density is interpreted as a double collision dissociation process of the type H2+ -> H20* -> H+. The influence of ion source parameters is also studied. Comparison is made with theory and the agreement is found to be good if one makes allowance for the dependence of dissociation upon the internuclear axis orientation.