Complete experiments on the non-adiabatic coupling in three particle continuum states
Final Report Abstract
1. We showed experimentally that an external electric field can be used to control the amplitudes of nonadiabatic paths taken by a dissociating molecule. This control was achieved by Stark-field mixing of H3 Rydberg states which follow different decay paths. The final state continuum is in each path formed by three-particle wave packets of slow neutral hydrogen atoms in their electronic ground state. Their momentum vector correlations show signs of interference, since the molecule can access the identical continuum via two distinctly different paths, involving different non-adiabatic coupling mechanisms. 2. We discovered that three-particle dissociation of high-lying Rydberg states of H3 , in the immediate vicinity of the ionization threshold, can be induced by an external electric field. The momentum vector correlation map of the center-of-mass motion of the fragments is found to change rapidly with increasing electronic energy. Near and above threshold substantial contributions of fragment orientations which are characteristic for near-linear geometry appear, i.e. two atoms with opposing momenta, the third atom being nearly at rest. This finding is similar to that found in dissociative recombination of cold H3+ -ions with slow electrons. We suggest the likely dissociation paths responsible for the observed correlation. 3. We studied the correlation pattern in the center-of-mass motion of the three fragments from dissociation of well-defined Rydberg states of D3. Dissociation of the molecules was induced by an external electric field. Through a comparison with results obtained in radiative cascading we showed that the correlation pattern is that of the short lived 2s 2A1' electronic state, of which a tiny amplitude is admixed by the external electric field. Similar experiments were conducted for H3. We compared our results with the predictions by Lehner and Jungen for predissociation of the 2s 2A1' state and find general agreement. Our work shows for the first time that it is possible to reconstruct the phase-space dependence of nonadiabaticity in a polyatomic molecule from the experimentally observed vector correlation.
Publications
- Experimental and quantum chemical studies on the three-particle fragmentation of neutral triatomic hydrogen. Phys. Rev. A 72 062506 (2005)
U. Galster, F. Baumgartner, U. Müller, H. Helm, and M. Jungen
- Experimental Observation of Non-Adiabatic Coupling in the H3 -Molecule
U. Galster, F. Baumgartner, H. Helm, and M. Jungen
- Double electron transfer in H − + H + collisions. Phys. Rev. Lett. 99 173202 (2007)
H. Brüning, H. Helm, J.S. Briggs and E. Salzborn
- Momentum vector correlation maps for three-particle fragmentation of neutral triatomic hydrogen near its ionization threshold. Phys. Rev. A 82 052523 (2010)
P. Fechner and H. Helm
- Stark field control of non-adiabatic dynamics in triatomic hydrogen. Phys. Rev. Lett. 104 103002 (2010)
F. Baumgartner and H. Helm
