The interaction of Cd(S-1:5s(2), P-3,P-1:5s(1)5p(1)) and Hg(S-1:6s(2), P-1,P-3:6s(1)6p(1)) with GeH4 were studied by means of Hartree-Fock self-consistent field (SCF) and multiconfigurational SCF plus variational and multireference second order Moller-Plesset perturbational configuration interaction (CIPSI) calculations, using relativistic effective core potentials. It was found that both metal atoms in their P-3(ns(1)np(1)) state break spontaneously the Ge-H bond of the germane molecule, giving place to the MH+GeH3 (M = Cd, Hg) final products. For both atoms, the P-1(ns(1)np(1)) state is also inserted in the Ge-H bond and the corresponding interaction surface shows an avoided crossing with the lowest-lying X (1)A' potential surface adiabatically linked with the M(S-1:ns(2)) + GeH4. This interaction leads eventually to the MH + GeH3 products. The HMGeH3 X (1)A(1) (M = Cd, Hg) intermediate molecules, diabatically correlated with the M(P-1:ns(1)np(1)) + GeH4, which lie 13.6 and 21 kcal/mol, respectively, above the ground state reactants, have been carefully characterized as well as the dissociation channels leading to the MH + GeH3 and H + MGeH3 products. These products are reached from the HMGeH3 intermediates without activation barriers. Accurate energy differences for all these species are reported. This work suggests that the simultaneous photoexcitation of Cd and Hg atoms in the presence of silane and germane molecules in the gas phase could be used to produce better quality a-SiGe:H thin films. (C) 2001 American Institute of Physics.