PROTON CAPTURE AND LOSS IN IONMOLECULE COLISIONS.

IBÁÑEZ, SANTIAGO; ALESSI, MARIANA; FREGENAL, DANIEL; FOCKE, PEDRO; BERNARDI, GUILLERMO; SUÁREZ, SERGIO

Freiburg, Alemania

Conferencia; XXV International Conference on Photonic, Electronic and Atomic Collisions; 2007

The dynamics of capture of atomic hydrogen by ions of noble gases interacting with H2 or hydrocarbons has been object of several studies due to its importance in stellar physics and in atmospheric processes. Studies for energies up to 200 eV/u reported evidences of H capture to the continuum of Ar+ and Kr+ projectiles. Such results show the existence of a peak of H+ centered at the velocity of the projectile, which has been interpreted in terms of a two-steps mechanism suggested by Thomas. In this work we studied the following type of collisions: P+ + (H+T)-> P+ + H+ + T and (P+T)+ + T -> P+ + H+ + T, where P is the projectile (Kr and Xe), T is the active target (CH4 and Ar), and H+ the ion exchanged. The projectile energy range is 175 to 500 eV/u. Experimentally, we separate the ion beams corresponding to different isotopes of Kr and Xe. For instance, in the case of Kr, we distinguish between stable isotopes 80, 82, 83, 84 and 86. In the case of 20 keV XKr+ on CH4, with X = 82, 84 and 86, a very well defined peak centered at the velocity of projectile is observed only for the collisions corresponding to the isotope 84. If each isotope is poorly contaminated with hydrogen, then the isotope 84Kr+ is a combination of 84Kr+ and (83KrH)+. On the other hand isotopes 82 and 86 are not contaminated. So we interpret this result as a H+ loss to the continuum of Kr projectiles. The presence of hydrogen in the ion beam is due to contamination in the ion source.