Laser-Induced Desorption of CO from Cr_2O_3 (0001): Ab Initio Calculation of the Four-Dimensional Potential Energy Surface for an Intermediate Excited State

摘要

Ab initio cluster calculations for an excited state of the system CO/Cr_2O_3 (0001) are presented. A CO(a ~3∏)-like state generated by an internal electronic excitation of the CO molecule (5σ → 2π) is considered to be a possible intermediate for the laser-induced desorption of CO from Cr_2O_3 (0001). A four-dimensional potential energy surface (PES) for this state is calculated at the CASSCF level of theory. A few possible alternatives for the desorption intermediate are also discussed. The interaction mechanism between the excited CO molecule and the surface is analyzed, and it is shown that the change of symmetry of the quadrupole moment of the CO molecule is responsible for the topology of the calculated PES.