A theoretical approach to the photochemical activation of matrix isolated aluminum atoms and their reaction with methane

The photochemical activation of Al atoms in cryogenic matrices to induce their reaction with methane has been experimentally studied before. Here, a theoretical study of the nonadiabatic transition probabilities for the ground (2P:3s23p1) and the lowest excited states (2S:3s24s1 and 2D:3s23d1) of an aluminum atom interacting with a methane molecule (CH4) was carried out through ab initio Hartree-Fock self-consistent field calculations. This was followed by a multiconfigurational study of the correlation energy obtained by extensive variational and perturbational configuration interaction analyses using the CIPSI program. The 2D state is readily inserted into a C-H bond, this being a prelude to a sequence of avoided crossings with the initially repulsive (to CH4) lower lying states 2P and 2S. We then use a direct extension of the Landau-Zener theory to obtain transition probabilities at each avoided crossing, allowing the formation of an HAlCH3 intermediate that eventually leads to the final pair of products H+AlCH3 and HAl+CH3.