Weakly-bound clusters of atmospheric molecules: infrared spectra and structural calculations of (CO2)n-(CO)m-(N2)p, (n,m,p) = (2,1,0), (2,0,1), (1,2,0), (1,0,2), (1,1,1), (1,3,0), (1,0,3), (1,2,1), (1,1,2)

Structural calculations and high-resolution infrared spectra are reported for trimers and tetramers containing CO2 together with CO and/or N-2. Among the 9 clusters studied here, only (CO2)(2)-CO was previously observed by high-resolution spectroscopy. The spectra, which occur in the region of the nu(3) fundamental of CO2 (approximate to 2350 cm(-1)), were recorded using a tunable optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. The trimers (CO2)(2)-CO and (CO2)(2)-N-2 have structures in which the CO or N-2 is aligned along the symmetry axis of a staggered side-by-side CO2 dimer unit. The observation of two fundamental bands for (CO2)(2)-CO and (CO2)(2)-N-2 shows that this CO2 dimer unit is non-planar, unlike (CO2)(2) itself. For the trimers CO2-(CO)(2) and CO2-(N-2)(2), the CO or N-2 monomers occupy equivalent positions in the 'equatorial plane' of the CO2, pointing toward its C atom. To form the tetramers CO2-(CO)(3) and CO2-(N-2)(3), a third CO or N-2 monomer is then added off to the 'side' of the first two. In the mixed tetramers CO2-(CO)(2)-N-2 and CO2-CO-(N-2)(2), this 'side' position is taken by N-2 and not CO. In addition to the fundamental bands, combination bands are also observed for (CO2)(2)-CO, CO2-(CO)(2), and CO2-(N-2)(2), yielding some information about their low-frequency intermolecular vibrations.