Angular spread of hydrogen atoms formed by electron capture and dissociation of H+, H2+ and H3+ in H2, H2O and C8F16 at energies of 2$middot$5 to 15 keV

Data are presented on the angular spread of neutral atoms formed by electron capture and dissociation of H + , H 2 + and H 3 + in H 2 , H 2 O and C 8 F 16 targets. Measurements were made at energies of 2·5 to 15 keV and for a range of target densities. The results are presented as the fraction transmitted through an aperture of a given half-angle. It is deduced that the angular spread of atoms from H 2 + and H 3 + molecular ion beams was predominantly due to the internal excitation energy of the molecular ions and not to simple scattering, even at the lower energies. The angular spread of atoms formed by electron capture by H + in H 2 O varied with energy as E −0·6 ; this is compared with the cross section for single scattering of H + on oxygen atoms obtained from the classical theory of Firsov, which varies as E −1 .