Vibrational spectra and structures of SinC clusters (n = 3–8)

Abstract

The effects of doping bare silicon clusters with carbon on their physical properties are of fundamental interest for the chemistry of the interstellar medium and the development of novel nanostructures in materials science. Carbon-doped silicon clusters (Si_nC, n = 3–8) are characterized in the gas phase with infrared-ultraviolet two-color ionization (IR-UV2CI) spectroscopy, mass spectrometry, and quantum chemical calculations. Structural identification is achieved by comparing the measured and calculated vibrational absorption spectra of the low-energy Si_nC isomers identified by global optimization algorithms. Except for planar Si₃C, the most stable Si_nC clusters have three-dimensional configurations. While the Si₃C and Si₆C structures are uniquely assigned, several stable isomers of Si₄C, Si₅C, Si₇C, and Si₈C may co-exist under the present experimental conditions. Interestingly, some of the structures observed here are different from the ground state structures predicted previously. For the small neutral clusters (n ≤ 5), structures similar to those reported previously for the anions are observed. The highly stable Si₃C unit with a nearly linear Si–C–Si motif is identified as characteristic building block in several of the most stable Si_nC structures. In all identified structures, a large negative charge of almost −2e is located on the C atom, indicating its role as electron donor in the Si_n host moiety. The B3LYP/cc-pVTZ level proves reliable in finding the experimentally observed isomers.