THE OPTICAL SPECTRUM OF THE SILICON TERMINATED CARBON CHAINS SiCnH
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Publisher:Ohio State University
The gas phase optical spectra of the silicon terminated carbon chains, SiC$_n$H (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.
Author Institution: IRAP; Universite de Toulouse, UPS; CNRS; 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France and Harvard-Smithsonian Center for Astrophysics; Cambridge, MA 02138, and School of Engineering & Applied Sciences; Harvard University, 29 Oxford St., Cambridge, MA 02138; Harvard-Smithsonian Center for Astrophysics; Cambridge, MA 02138, and School of Engineering & Applied Sciences; Harvard University, 29 Oxford St., Cambridge, MA 02138; Department of Chemistry, Virginia Tech, Blacksburg, VA 24061
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