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 Title: A STRANGE COMBINATION BAND OF THE CROSS-SHAPED COMPLEX CO2-CS2 Author(s): McKellar, Bob Contributor(s): Moazzen-Ahmadi, Nasser Subject(s): Clusters/Complexes Abstract: The spectrum of the weakly-bound chem{CO_2}-chem{CS_2} complex was originally studied by the USC group,footnote{C.C. Dutton, D.A. Dows, R. Eikey. S. Evans, R.A. Beaudet, J. Phys. Chem. A textbf{102}, 6904 (1998).} using a pulsed supersonic expansion and a tunable diode laser in the chem{CO_2} nub{3} region. Their derived structure was nonplanar X-shaped ($C_{2v}$ symmetry), a relatively unusual geometry among linear molecule dimers. Very recently, there has been a detailed theoretical study of this complex based on a high-level $ab~initio$ potential surface.footnote{J. Brown, X.-G. Wang, T. Carrington, Jr., G.S. Grubbs II, and R. Dawes, J. Chem. Phys. textbf{140}, 114303 (2014).} The theoretical ground state is X-shaped, in good agreement with experiment, and a very low-lying (3 wn~at equilibrium, or 8 wn~zero-point) slipped-parallel isomer is also found. We report here two new combination bands of X-shaped chem{CO_2}-chem{CS_2} which involve the same nub{3} fundamental (2346.546 wn) plus a low-frequency intermolecular vibration. The first band has $b$-type rotational selection rules (the fundamental is $c$-type). This, and its location (2361.838 wn), clearly identify it as being due to the intermolecular torsional mode. The second band (2388.426 wn) is $a$-type and can be assigned to the chem{CO_2} rocking mode. Both observed intermolecular frequencies (15.29 and 41.88 wn) are in extremely good agreement with theory (15.26 and 41.92 wn).$^{b}$ The torsional band is well-behaved, but the 2388 wn~band is bizarre, with its $K_{a}$ = 2 $leftarrow$ 2 and 4 $leftarrow$ 4 components displaced upward by 2.03 and 2.62 wn~relative to the $K_a$ = 0 $leftarrow$ 0 origin (odd $K_a$ values are nuclear spin forbidden). A qualitatively similar shift (+2.4 wn) was noted for the (forbidden) $K_{a}$ = 1 level of this mode by Brown et al.,$^{b}$ but the calculation was limited to $J$ = 0 and 1. These huge shifts are presumably due to hindered internal rotation effects. Issue Date: 24-Jun-15 Publisher: International Symposium on Molecular Spectroscopy Citation Info: ACS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/79152 Date Available in IDEALS: 2016-01-05
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