Emission cross-section measurements of low energy He+ ions with Cl2, Br2, I2 reactions

The cross sections for production of emission lines in the 60 nm to 870 nm region were measured for the collision of 100 eV He+ ions with Cl2, Br2, and I2. These cross section measurements were made with an ion beam apparatus. Only emissions from transitions from excited electronic states with lifetimes shorter than a μsec were measured. The dependence of the cross sections on the kinetic energy of the He+ ions between 2 to 170 eV was determined by use of the more intense emission lines. The total cross section obtained for emissions between 90 nm and 870 nm for chlorine is 5.0 A2; of this, 3.8 A2 is for emissions in the VUV region. Emissions from excited neutral chlorine atoms account for at least 85 percent of the total cross section. Of the cross section for production of emission from excited neutral chlorine atoms, 80 percent is caused by direct excitation with the remainder resulting from cascading. The total cross section obtained for emissions between 80 nm and 870 nm for bromine is 14.9 A2; of this, 11.9 A2 is for emissions in the VUV region. Emissions from excited neutral bromine atoms account for at least 85 percent of the total cross section. Of the cross section for production of emission from excited neutral bromine atoms, 75 percent is caused by direct excitation with the remainder resulting from cascading. The total cross section obtained for emissions between 100 nm and 870 nm for iodine is 15.9 A2; of this, 14.4 Z2 is for emissions in the VUV region. The proportion of the total cross section for the production of emissions from singly-ionized iodine atoms is much larger than for either the chlorine or bromine reactions. In all three systems dissociative charge transfer appears to be the predominant reaction process for the production of emissions in the 60 nm to 870 nm spectral region