Ejection anisotropy in three-atom Coulomb explosions

Abstract

Coulomb explosion imaging has been used to explore anisotropies in the fragment angular distribution associated with the symmetric six-electron Coulomb explosion channel of CO{sub 2} and NO{sub 2} induced by 100 fs, 10{sup 15} W/cm{sup 2} radiation at 800 nm and leading to doubly charged atomic ions. Specific precursor molecular geometries (bond angles prior to explosion) and orientations of the molecular axis (the line connecting the two outer atoms in the system) relative to the polarization axis were isolated for analysis by exploiting the correlation among the atomic ions ejected simultaneously. The effective orientation of the precursor molecular axis is preferentially along the polarization axis for both CO{sub 2} and NO{sub 2} with respective distributions and widths of cos{sup 39} {theta} ({delta}{theta}{approx_equal}22 deg.) and cos{sup 25} {theta} ({delta}{theta}{approx_equal}27 deg.), which are substantially narrower than that of H{sub 2}, cos{sup 19} {theta} ({delta}{theta}{approx_equal}31 deg.). The widths and distributions are found to be nearly independent of bond angle over a wide range of bond angles (35 deg. and 55 deg. for CO{sub 2} and NO{sub 2}, respectively). The narrowing of the width of the distribution from H{sub 2} to CO{sub 2}, combined with the independence of bond angle are consistent with (1)more » an increasing moment of inertia (2) an increasing final charge state, and (3) an increasing precursor molecular ion ionization stage.« less