Berlin 2005 – wissenschaftliches Programm
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MO: Molekülphysik
MO 31: Ultrafast Photochemistry
MO 31.8: Vortrag
Montag, 7. März 2005, 12:15–12:30, HU 2091
Attosecond quantum dynamics of bond breaking studied by neutron-proton scattering — •C. Aris C.-Dreismann1 and Tyno Abdul-Redah2 — 1Inst. f. Chemie, Stranski Lab., TU Berlin, D-10623 Berlin — 2ISIS Facility, R.A.L., Oxfordshire, OX11 0QX, U.K.
Compton scattering of neutrons from protons takes place in the attosecond time range. Due to the large energy and momentum transfers applied in these experiments, the chemical H-X bonds (X: O, C, N, etc.) are broken. Several experiments on liquid and solid samples containing protons show a striking shortfall in the intensity of epithermal neutrons scattered by the protons [1,2]. E.g., neutrons colliding with water for just attoseconds will see a ratio of H to O of roughly 1.5 to 1, instead of 2 to 1 [1,2]; accordingly, the measured ratio of H to C in benzene is roughly 4 to 6, instead of 6 to 6. Recently this effect has been confirmed using electron-proton Compton scattering (ECS) from a solid polymer [1b,2]. Recall that electrons and neutrons interact with protons via fundamentally different forces – electromagnetic and strong. Theoretical considerations support the presence of attosecond quantum entanglement in the dynamics of the protons and the surrounding electrons. Current NCS experiments on liquid hydrogen (H2, D2, and HD; T = 20 K) demonstrate that spin-entanglement between two protons play no role in this effect. Our results indicate hitherto unknown features of sub-femtosecond dynamics of chemical bonds.
[1] (a) C. A. Chatzidimitriou-Dreismann et al., Phys. Rev. Lett. 79, 2839 (1997); and (b) Phys. Rev. Lett. 91, 057403 (2003). [2] Cf.: Physics Today, p. 9, Sept. 2003; Physik in unserer Zeit 35(4), 174 (2004).