Knowledge Bank

Infrared spectra of carbon disulfide trimer formed in a pulsed supersonic slit-jet expansion are obtained via direct absorption of a tuneable diode laser in the region of the CS$2$ $\nu 3$ fundamental band ($\sim$ 1535 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$). Two bands sharing the same lower state were assigned to (C$\mathrm{<mrow\; data-mjx-texclass="ORD">32</mrow>}$S$2$)$3$. These correspond to the two infrared active vibrations (a parallel and a perpendicular band) of the constituent CS$2$ asymmetric stretches. The weaker perpendicular band is centered at 1524.613 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. It is shifted by $-$10.74cm$^{-1}$ with respect to the free CS$2$ monomer. The parallel band which is significantly stronger is centered at 1545.669 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. It has a vibrational shift of $+$10.31cm$^{-1}$. The transitions with $K\ne 3n$ and those with $J=$ odd and $K=0$ in the ground state are absent in both bands. This rigorously establishes that this isomer of carbon disulfide trimer has $D3$ symmetry. Thanks to the symmetry, only two parameters, the C-C distance and the angle between a monomer axis and the plane containing the C atoms, are required to fully define the structure of the trimer. These were determined to be 3.811 {\AA} and 61.8$^irc\}$, respectively. In addition, a parallel band corresponding to a single $\mathrm{<mrow\; data-mjx-texclass="ORD">34</mrow>}$S substitution was observed around 1544.46 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. Results from this band are in complete agreement with those of the two bands for (C$\mathrm{<mrow\; data-mjx-texclass="ORD">32</mrow>}$S$2$)$3$.