Relativistic potential energy surfaces of initial oxidations of Si(100) by atomic oxygen: The importance of surface dimer triplet state

The non-relativistic and relativistic potential energy surfaces (PESs) of the symmetric and asymmetric reaction paths of Si(100)-2×1 oxidations by atomic oxygen were theoretically explored. Although only the singlet PES turned out to exist as a major channel leading to on-dimer product, both the singlet and triplet PESs leading to on-top products are attractive. The singlet PESs leading to the two surface products were found to be the singlet combinations (open-shell singlet) of the low-lying triplet state of surface silicon dimer and the ground ³P state of atomic oxygen. The triplet state of the on-top product can also be formed by the ground singlet state of the surface silicon dimer and the same ³P oxygen. The attractive singlet PESs leading to the on-dimer and on-top products made neither the intersystem crossings from triplet to singlet PES nor high energy ¹D of atomic oxygen necessary. Rather, the low-lying triplet state of surface silicon dimer plays an important role in the initial oxidations of silicon surface.