Classical and quantum aspects of the dissociation of HCl⁺ on MgO(001) have been investigated. This system is unique because it can dissociate to either H+Cl⁺ and H⁺+Cl channels, with quite different dynamic behaviors. The molecule adsorbs on the surface with the hydrogen down, forming a strong H-bond with a surface anion. The dissociation results in collisions of H(or H⁺) with the surface. We observed significant perturbation in the absorption spectrum due to surface induced stablization. Our results also indicated that several pronounced peaks in the product angular distribution are due to surface-induced rainbow effect. Some observed features are generic for surface photodissociation of H-containing molecules.

Fig. 1: Potential and wave packet motion on an excited state

Fig. 2: Classical trajectories on the same state

Fig. 3: Classical deflection function: rainbow effect

Quicktime Movie: Wave packet motion

References:

[1] T. Seideman and H. Guo, J. Chem. Phys., 103, 2745 (1995). Photodissociation of HCl⁺/MgO(001): the static and dynamic effects of the surface.

[7] H. Guo and T. Seideman, J. Chem. Phys., 103, 9062 (1995). Quantum mechanical studies of photodesorption of ammonia from a metal surface: isotope effect, final state distributions and desorption mechanisms