Carbon-13 studies of sulphur-terminated carbon chains: chemical bonding, molecular structures, and formation pathways

Abstract

The rotational spectra of the singly substituted carbon-13 isotopic species of six sulphur-terminated carbon chains have been detected between 5 and 40 GHz using a supersonic discharge jet source in combination with a cavity Fourier transform microwave spectrometer. These molecules are , a closed-shell isomer of , and five radicals: , , , and . Experiments were carried out with precursors enriched in C, either high purity , a statistical sample of C/C acetylene, or . From the C hyperfine coupling constants, the unpaired electronic density along the chain can be quantified for the radical species, while precise experimental structures () can be derived for each chain except by a least-squares fit to the rotational constants. The use of is particularly revealing in that it provides important clues as to the major formation pathway for each chain in our discharge nozzle. Somewhat surprisingly, C from this precursor appears to be substituted in one of three distinct ways: statistical, a single C site, or not at all. This propensity is molecule specific, implying that multiple formation pathways are operative.