Computational study of Si2H and Si2H2 species as candidates of interstellar molecules.

Disilicon hydrides as candidates of interstellar molecules have been studied employing density functional and coupled cluster quantum chemical methods. Potential energy surfaces of Si2H and Si2H2 in the electronic ground state reveal that several isomeric structures are energetically well separated. This means that these isomers can be distinguished in low-temperature conditions such as the interstellar medium due to the disfavor of their inter-conversions. Two nearly degenerate states exist for cyclic structures of Si2H that both can be possible isomers. In the case of Si2H2, four isomeric structures are well separated by energy barriers for isomerization processes between them. We have also examined potential energy surfaces in the lowest excited state for the Si2H and Si2H2 species and found that the energies of several isomeric species in the ground state are very close to their energies in the lowest excited states. The reactivity of Si2H and Si2H2 with hydrogen atom is examined and possible formation mechanisms of Si2H and Si2H2 molecules via neutral-neutral reactions are discussed as astrophysical implications. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]