Seminar by Prof. Jacques Robert 'Metastable hydrogen atoms from H2 molecules: towards twin atoms'

Speaker: Prof. Jacques Robert
Laboratoire Aimé Cotton CNRS, Univ Paris Sud 11, France

Seminar Title:
'Metastable hydrogen atoms from H2 molecules: towards twin atoms'

Seminar Abstract:
The dissociation of a diatomic molecule in a pair of atoms is a well know problem, and it is also well known that the two fragments, say twin atoms for a homonuclear diatomic molecule, will share some coherence between them because they are linked to the same molecular state. The signature of the coherence between the fragments is revealed in coincidence experiments, for the centre of mass and relative motions, but a finer analysis requires also detecting the spin coherence between the atoms, in the same way that it is done for twin photons.
The superexcited states of the H2 molecules have been shown to be good candidates to perform twin photons experiments, using the dissociation in twin H(2p) atoms that dissociates in twin Lyman-α photons . Spin analysis of H(2s) atom can be achieved through the use of Stern Gerlach interferometry, it is legitimate to investigate the dissociation of superexcited states of the H2 molecule in pairs of twin spin-polarized H(2s) atoms. Other systems are or have been in focus such as Hg2 the first system that deserved a study and there is work in progress in cold or ultra-cold conditions.
We present the first step of this study where we have revisited the dissociation of H2 molecules excited by electron impact, using a molecular nozzle beam in order to use molecules with cold internal degrees of freedom and high intensity fluxes. We have investigated the production of fast metastable H(2s) coming from the dissociation of cold H2 molecules produced in a Campargue nozzle beam after their crossing with an electron beam emerging from a high intensity pulsed electron gun. We have addressed dissociation by electron impact, rather than by photo dissociation, in order to avoid limitations by the selection rules governing the radiative transitions, encountered in the previous experiments. With one detector, placed several centimetres away from the collision centre, one can analyse the neutral fragments as a function of their time-of-flight (TOF) through Lyman-α detection. Measurements with two detectors show evidence, of coincidence of pairs of H(2s) coming from the dissociation of doubly excited states of H2, populated by electron-impact excitation.

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