The Rovibrational Spectrum and Structure of the Weakly Bound CO2−CS2 Complex

The rovibrational spectrum of the weakly bound complex CO 2 −CS 2 was observed by exciting the asymmetric stretch of the CO 2 moiety near 2349 cm -1 . The complex was formed by the supersonic expansion of a 1:2 mixture of CO 2 and CS 2 in helium and had a nonplanar X-shaped structure. The intermolecular distance is 3.392 Å with a dihedral angle of 90°. The band center is located at 2346.5448 cm -1, with ground-state rotational constants of A ‘‘ = 0.08590 cm -1, B ‘‘ = 0.04634 cm -1, and C ‘‘ = 0.03546 cm -1 and centrifugal distortion constants of D j ‘‘ = −1.37 × 10 -7 cm -1, D k ‘‘ = 1.06 × 10 -6 cm -1, and D jk ‘‘ = −1.01 × 10 -6 cm -1 . The excited-state constants are similar to the ground-state constants. A portion of the potential energy surface was modeled through the use of a Buckingham atom−atom potential and a quadrupole−quadrupole electrostatic potential. Calculations for the CO 2 −CS 2 and (CO 2 ) 2 complexes produced structures in agreement with experimental results. Although the CO 2 −CS 2 configuration is controlled by the quadrupole−quadrupole interactions, the atom−atom interactions predominantly determine the energy of the dimer. Because the magnitude of the CS 2 quadrupole was increased in the electrostatic potential, the structure shifted from nonplanar X-shaped to a planar parallel configuration.