FORMATION OF HIGHLY EXCITED HYDROGEN-ATOMS BY ELECTRON-CAPTURE IN PROTON COLLISIONS

The production of highly excited hydrogen atoms in proton collisions with the inert gases, hydrogen and nitrogen has been investigated within the energy range 4-20 keV. Cross sections for the formation of atoms in states with principal quantum number, n, between 24 and 40 have been determined using the field ionisation technique and found to scale as n-3. A comparison with optical data for n<or=3 shows that this scaling law applies down to n=2 in this energy range. The production of excited atoms is not in agreement with calculations using the Brinkman-Kramers approximation. The maxima in the cross sections are, however, in accord with simple semi-empirical formulae.