The rovibrational absorption spectrum of the weakly bound cluster CO 2 -N 2 O has been observed in the region of the ν 3 CO 2 asymmetric stretch (∼2350 cm -1 ). Clusters were formed by supersonic expansion of a mixture of N 2 O:CO 2 in a 4:1 ratio using He carrier gas. Approximately 340 lines have been assigned. Both parallel and perpendicular transitions were observed. The ground state rotational constants A, B, and C are 0.294 924-(12), 0.058 004(6), and 0.048 400(6) cm -1 , respectively. The quartic centrifugal distortion constants are D j ) 5.03(17) × 10 -7 cm -1 , D jk ) -3.92(9) × 10 -6 cm -1 , D k ) 1.26(2) × 10 -5 cm -1 , δ j ) 1.61(92) × 10 -8 cm -1 , and δ k ) 1.77(80) × 10 -6 cm -1 . Ab initio calculations for several CO 2 -N 2 O equilibrium structures have been done on the Hartree-Fock self-consistent field level using a 6-311g* basis set. Møller-Plesset MP2 and MP3 calculations were carried out for the two possible slipped parallel configurations of the dimer. The planar slipped parallel geometry with the oxygen atom of N 2 O nearest the CO 2 monomer was found to be the most stable structure. The spectral constants and stabilization energies were compared to those of the CO 2 and N 2 O homodimers. A planar slipped parallel geometry is observed with the O of N 2 O nearly over the C of CO 2 . R cm and θ are 3.4701 Å and 60.1°, respectively, assuming the CO 2 and N 2 O are parallel to each other.

The rovibrational spectrum of the weakly bound complex CO2−CS2 was observed by exciting the asymmetric stretch of the CO2 moiety near 2349 cm-1. The complex was formed by the supersonic expansion of a 1:2 mixture of CO2 and CS2 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 CO2−CS2 and (CO2)2 complexes produced structures in agreement with experimental results. Although the CO2−CS2 configuration is controlled by the quadrupole−quadrupole interactions, the atom−atom interactions predominantly determine the energy of the dimer. Because the magnitude of the CS2 quadrupole was increased in the electrostatic potential, the structure shifted from nonplanar X-shaped to a planar parallel configuration.