Hannover 2003 – wissenschaftliches Programm

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MO: Molekülphysik

MO 8: Photoelektronenspektroskopie, Photodissoziation

MO 8.8: Vortrag

Donnerstag, 27. März 2003, 15:45–16:00, B 305

Evidence of a critical internuclear distance in Coulomb explosion of H₂ ⁺ and D₂ ⁺ — •Domagoj Pavičić, Andreas Kiess, Theodor W. Hänsch, and Hartmut Figger — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching

Since the development of novel sources of ultrashort intense laser pulses, much attention has been directed to H₂ ⁺ in intense laser fields. However, almost all experiments have started from neutral H₂ as a precursor. Contrary to that, we investigated Coulomb explosion of H₂ ⁺ and D₂ ⁺ in ion beams observing for the first time peak structure in fragment kinetic energy spectra. H₂ ⁺ and D₂ ⁺ were produced in a DC-discharge ion source and were formed into well collimated ion beams. Laser pulses with duration of 80 fs and central wavelength of 790 nm were focused on the ion beam. The velocity distribution of fragments from photodissociation and Coulomb explosion channel was measured by imaging them onto a two-dimensional detector. The photodissociating fragments originating from different molecular vibrational states of H₂ ⁺, D₂ ⁺ and recently also HD ⁺ were resolved. The ratio of the number of H to the number of D fragments of HD ⁺ will give us better understanding of symmetry breaking effects in the dissociation process. The peaked structure observed in the Coulomb explosion spectra at intensities near the threshold could be fitted to the energies that are expected from one- and net two-photon absorption, but shifted by 1.07 eV. We interpret the fragment spectra as a result of Coulomb explosion at a well defined No-dqcriticalNo-dq distance, which adds the same kinetic energy to all fragments and therefore preserves the original kinetic energy distribution from the dissociation channel.