Experimental studies of collisional breakup of slow hydrogen molecular ions

Itzik Ben-Itzhak, A. Max Sayler, Nora G. Johnson, Jack W. Maseberg, Dag Hathiramani, Kevin D. Carnes
James R. Macdonald Laboratory, Department of Physics,
Kansas State University, Manhattan, KS, USA

Collision induced dissociation (CID, e.g. H2+ + Ar - H+ + H + Ar) and dissociative capture (DC, e.g. H2+ + Ar - H + H + Ar+), are the main processes occurring in collisions between slow (keV) molecules and atomic targets. Our studies are focused on collisions between simple molecular ions, like H2+, HD+ and HeH+, and noble gas targets. The kinetic energy release upon dissociation and the angular distribution of the fragments were determined using a coincidence 3D momentum imaging technique, which allows separation of the simultaneously measured CID and DC reaction products. Furthermore, CID caused by an electronic excitation to a repulsive state is distinguished from that caused by a vibrational/rotational excitation by the difference in momentum transfer to the projectile. Each process exhibits a different angular distribution, and in some cases the angular distribution depends on the bond length of the molecular ion. For example, vibrational CID is strongly favored for molecular ions aligned perpendicular to the beam direction and they dissociate preferentially along the momentum transfer. Isotopic preferences in HD+ + Ar collision induced dissociation are under study.

This work was supported by the Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Submitted to CAARI, August 2006 in Fort Worth, TX.

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