Knowledge Bank

The gas phase optical spectra of the silicon terminated carbon chains, SiCH (n=3-5) formed in a silane acetylene discharge, have been investigated by R2C2PI and LIF/DF and will be reported here for the first time. Complementary to the experimental work, a theoretical investigation was undertaken with coupled cluster methods to garner a comprehensive understanding of the molecular structures and electronic properties of these systems. For the linear chains where there is an odd number of carbon atoms (SiC$3$H and SiC$5$H), the observed transitions are primarily from a $2\Pi$ ground state to a $2\Sigma$ state, but as in the case of isovalent carbon chains there are some Herzberg-Teller active modes from an excited $2\Pi$ state. While a strong $\Pi -\Pi$ transition is predicted for SiC$4$H, the spectrum is dominated by relatively dark sigma state which is vibronically coupled to the bright $2\Pi$ state. In contrast to the odd carbon chains, which exhibit relatively sharp spectral features and lifetimes in the 10-100,ns regime, SiC$4$H shows broadened spectral features consistent with a ca. 10,ps lifetime, and a subsequent long-lived decay ($>30$,microseconds) which we tentatively interpret in terms of mixing with a nearby quartet state arising from the same electronic configuration, a process unavailable for the odd chains.