Weakly-bound van d r \i\ aal clu t r of 2 0 and C02 were studied in a pulsed supersonic slit expansion probed with a tunable diode la er. The first observation of a polar isomer of N 2 0 dim r in t h region of the v1 fundamental band wa mad . Structural parameter were determined by recording and analyzing the spectra of the 15 N- ubstituted isotopic form and h normal pecies. The polar form of the dimer has a lipped parallel t ructur, rather similar to the slipped antiparallel structure of the nonpolar form but wit h a slightly larger intermolecular distance. Litrature assignments of the combination band (rv2 249 cm- 1) involving the intermolecular torional vibration was corrected. In addition a higher frequency combination band involving the intermolecular disrotation of the monomers (Bu intermolecular bend) for both (14 2 0 )2 and (15 2 0 )2 were measured and analyzed. nitrous oxide trim r was also studied. A previous empirical structural culation on (14 2 0 )3 has suggested a noncy lie barrel-shaped structure; having no specific symmetry. In this structure, the t hr contiunt monomers are in equivalent giving n to the infrared band. We recorded and analyzed the three expected band for the 15 -substituted ioopic form and the normal pecie. Three weaker rim r combination bands were also observed. Each band involves the sum of one of the previously observed intramolecular trim r vibrations plus an intermolecular vibration (van der Waal str tch orb nd). Possible vibrational assignment forth combination band are discussed based on their rotational structure and t h ru ur of the trimer. W also carried out a number of new measurements on C0 2 cluster. Spectrum of the (12 C0 2 ) 2 in the v3 fundamental region has been previously studied showing a planar lipped-parallal structure with c ntrosymmetric C2h ymmetry. Here, we report our own analyses of t his band as well as analyses of t he spectra of t he (13 CO2 )2 and 12 CO2 - 13 CO2 , clarifying t he role of resonant and non-resonant vibrational shift . Moreover, observation of a combination band of the (12CO2 ) 2 provides the first experimental intermolecular vibrational frequency for the dimer. Possible vibrational assignments are discussed . Two new parallel bands of t he cyclic (12CO2)3 in the v3 fundamental region were also observed. This isomer of t he t rimer has been previously found to be a symmetric top with planar structure and C3h symmetry. The band were assigned as a combination of intramolecular CO2 monomer v3 stretch and intermolecular out-of-pl an torsion. This provides the first measurement of two intermolecular vibrational frequencies for the cyclic trimer.