Triatomic Hydrogen
Welcome to the Triatomic Hydrogen Group at the Department of Molecular and Optical Physics - University of Freiburg, Germany

Kinematically complete final state investigations of molecular photodissociation:
two- and three-body decay of laser-prepared H33s2A1'

U. Galster, P. Kaminski, M. Beckert, H. Helm, and U. Müller
Department of Molecular and Optical Physics, Albert-Ludwigs-Universität, Hermann-Herder-Strasse 3, D-79104  Freiburg, Germany


We have performed kinematically complete investigations of molecular photodissociation of triatomic hydrogen in a fast beam translational spectrometer recently built in Freiburg. The apparatus allows us to investigate laser-induced dissociation of neutral molecules into two, three, or more neutral products. The fragments are detected in coincidence and their vectorial momenta in the center-of-mass frame are determined. We demonstrate the potential of the method at the fragmentation of the 3 s21(N=1, K=0)state of triatomic hydrogen. In this state, three-body decay into ground state hydrogen atoms H+H+H, two-body predissociation into H+H2 (v, J), and photoemission to the H3 ground state surface with subsequent two-body decay are competing channels. In the case of two-body predissociation, we determine the rovibrational population in the H2 (v, J)fragment. The vibrational distribution of H2 is compared with approximate theoretical predictions. For three-body decay, we measure the six-fold differential photodissociation cross-section. To determine accurate final state distributions, the geometric collection efficiency of the apparatus is calculated by a Monte Carlo simulation, and the raw data are corrected for apparatus efficiency. The final state momentum distribution shows pronounced correlation patterns which are characteristic for the dissociation mechanism. For a three-body decay process with a discrete kinetic energy release we have developed a novel data reduction procedure based on the detection of two fragments. The final state distribution determined by this independent method agrees extremely well with that observed in the triple-coincidence data. In addition, this method allows us to fully explore the phase space of the final state and to determine the branching ratios between the two- and three-body decay processes.

©EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
EPJ D 17, 307 (2001)
The European Physical Journal D

33.80.Gj - Diffuse spectra; predissociation, photodissociation.
33.80.Rv - Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states).
34.80.Ht - Dissociation and dissociative attachment by electron impact.

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