Direct measurement of the orientation dependence of dissociative scattering of H2+ from Cu(111)

• Published in: Surface science 1992-05, Vol.269-270, p.213-218
• Main Authors: Rechtien, J.-H., Harder, R., Herrmann, G., Röthig, C., Snowdon, K.J.
• Format: Article
• Language: English
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(92)91252-7

We report a direct measurement of the molecular axis orientation dependence of dissociative neutralisation of 2.98 keV H2+ at a Cu(111) surface. The kinetic energy ϵ released and the final orientation θ of the molecular axis to the surface normal are derived from the measured laboratory-frame velocities of the neutral dissociation fragments. Above an incident beam perpendicular energy E⊥i ≈ 3.5 eV the ϵ energy distribution appears to consist of one structure peaking at or below ϵ ≈ 0.75 eV. As we reduce E⊥i, an additional broad structure peaking at ϵ ≈ 3 eV, θ ≈ 60° appears. The intensity ratio of these two structures remains approximately constant for E⊥i values below 1 eV. We propose that neutralisation occurs on the incident portion of the trajectory, primarily to the (surface modified) X1Σg+ state of H2, and furthermore, that the observed change of the spectrum with E⊥i may be related to reflection from (for E⊥i < 1 eV) and traversal over (for E⊥i > 1 eV) an activation barrier of height ∼ 1 eV on the H2/Cu potential energy surface.