Direct measurement of molecular breakup dynamics and vicinage effect of swift proton clusters using narrow nuclear resonance profiling

We report on the first direct observation of the evolution with time of the vicinage effect and Coulomb explosion for H 2 + and H 3 + molecules in a thick amorphous silica layer enriched with 18O atoms. High depth resolution is achieved by using the 18O ( p, α) 15N nuclear reaction narrow resonance around E R = 151 keV/nucleon (corresponding to a velocity V), and scanning the beam energy around E R . The results are well described when using a Coulomb screening radius r s ≈ (2/ π) R ad where R ad = V/ ω p is an adiabatic cut-off for a valence electron gas with plasmon frequency ω p ≈ 24 eV. The vicinage effect is reproduced when describing the experimental energy loss function of the target valence electron gas by a single Drude function with damping factor γ ≈ 22 eV and including multiple scattering on target nuclei.