Infrared bands of CS2 dimer and trimer at 4.5 cm-1

Abstract

We report observation of new infrared bands of (CS2)2 and (CS2)3 in the region of the CS2 ν1+ ν3 combination band (at 4.5 cm-1) using a quantum cascade laser. The complexes are formed in a pulsed supersonic slit-jet expansion of a gas mixture of carbon disulfide in helium. We have previously shown that the most stable isomer of (CS2)2 is a cross-shaped structure with D2d symmetry and that for (CS2)3 is a barrel-shaped structure with D3 symmetry. The dimer has one doubly degenerate infrared-active band in the ν1+ ν3 region of the CS2 monomer. This band is observed to have a rather small vibrational shift of -0.846 cm-1. We expect one parallel and one perpendicular infrared-active band for the trimer but observe two parallel and one perpendicular bands. Much larger vibrational shifts of -8.953 cm-1 for the perpendicular band and -8.845 cm-1 and +16.681 cm-1 for the parallel bands are observed. Vibrational shifts and possible vibrational assignments, in the case of the parallel bands of the trimer, are discussed using group theoretical arguments.

arXiv comment24 pages, 5 figures and 2 tables