München 2004 – wissenschaftliches Programm
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A: Atomphysik
A 15: Poster 2
A 15.19: Poster
Donnerstag, 25. März 2004, 14:00–16:00, Schellingstr. 3
HD + in an ionic beam in intense femtosecond laser fields — dissociation and ionization — •Andreas Kiess, Domagoj Pavičić, Theodor W. Hänsch, and Hartmut Figger — Max-Planck-Institut für Quantenoptik, Hans-Kopfermannstr. 1, 85748 Garching
After having investigated the two homonuclear isotopomers H2 + and D2 +, here we report on a study of the mixed heteronuclear ion HD+ in intense femtosecond laser fields. A fast (11 keV) and highly collimated ion beam is exposed to focused laser pulses with a pulse duration of 90 fs and intensities in the range of 1013 to 1015 W/cm2. The resulting atomic (H, D) and ionic (H+, D+) fragments were detected on a position-sensitive multichannel plate detector, thereby measuring their velocity distribution. In distinction to the photodissociation of H2 + and D2 +, HD+ can photodissociate via two competing channels, namely HD+ —→ H + D+ and HD+ —→ D + H+. This means that the electron has to make the choice in the dissociation process whether to join the proton or the deuteron. This offers an opportunity to measure the breakdown of the Born-Oppenheimer approximation. Besides the dissociation channels, HD+ can also undergo Coulomb explosion, HD+ —→ H+ + D+ + e−. All these channels can be separated in our experiment since the velocities of the H/H+ and D/D+ fragments differ by a factor of 2 as a consequence of momentum conservation. Furthermore, by electric deflection of the ionic fragments, the neutral fragments can be observed alone. In distinction to the homonuclear cases of H2 + and D2 +, the photodissociation of HD+ is characterized by three avoided potential curve crossings, corresponding to absorption of one, two and three photons.