Berlin 2001 – scientific programme

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MO: Molekülphysik

MO 6: Dissociation and other Collision Processes

MO 6.3: Talk

Tuesday, April 3, 2001, 16:30–16:45, H1058

Fragmentation of H₃⁺ after electron capture — •H. Kreckel¹, S. Krohn^1,2, L. Lammich¹, M. Lange¹, J. Levin¹, D. Schwalm¹, D. Strasser², A. Wolf¹, R. Wester¹, Z. Vager², and D. Zajfman² — ¹MPI für Kernphysik, Heidelberg, Germany — ²Weizmann Institute of Science, Rehovot, Israel

Triatomic molecular hydrogen (H₃/H₃⁺) has found much attention as the most fundamental polyatomic system. In particular, low-energy electron capture of H₃⁺ initiates dissociation via the repulsive ground-state potential surface of H₃, leading to three ground-state H atoms or to H₂(v) + H. Large discrepancies still exist between experiment and theoretical predictions for this process. Besides the basic interest, it is also a key process for the chemistry in diffuse interstellar clouds. At the TSR storage ring of the MPI für Kernphysik in Heidelberg a H₃⁺ beam was stored for several seconds, allowing relaxation to the vibrational ground state. The neutral fragments produced in a superimposed cold electron beam at near-zero relative energy (<10 meV) were then recorded using a two-dimensional imaging technique. From the kinetic energy release distribution of the two-body breakup (H₂(v) + H) the distribution of vibrational excitation of the remaining H₂ fragment could be extracted. The geometry of the three-body dissociation (H + H + H) was analyzed and compared to a Coulomb explosion measurement that reveals the structure of the stored molecular ion. It was found that the dissociation follows predominantly linear geometries, while the Coulomb explosion measurement reproduces the expected triangular shape of the H₃⁺ molecules before recombination. Supported by DIP and MINERVA.