Photodissociation of CH3Cl, C2H5Cl, and C6H5Cl on the Ag(111) surface: ab initio embedded cluster and configuration...

We report a comparative study of the photoinduced C-Cl bond cleavage in three Rd-Cl molecules (Rd=CH(3), C(2)H(5), and C(6)H(5) radicals) on the Ag(111) surface. The ground, lowest excited states as well as anion states of adsorbed molecules have been computed at their equilibrium geometry and along the C-Cl dissociation pathway using the ab initio embedded cluster and multireference configuration interaction methods. The anion state can be formed by photoinduced electron transfer from the substrate to an adsorbate and is strongly bound to the surface in contrast with the electronic states of the adsorbate itself, which are only weakly perturbed by the silver surface. The excitation energy of the anion state lies lower in the Franck-Condon region than that of the lowest singlet excited state for all adsorbates and correlates directly with the dissociation products: adsorbed chlorine atom and the gas phase or adsorbed radical for Rd=CH(3), C(2)H(5), and C(6)H(5), respectively. The computed redshift of the photodissociation spectrum for the substrate-mediated photodissociation process relative to the corresponding gas-phase reaction is approximately 2 eV for CH(3)Cl and C(2)H(5)Cl, and approximately 1 eV for C(6)H(5)Cl, which result is in good agreement with experimental data.