Spectra of clusters of nitrous oxide-acetylene trimer formed in a pulsed supersonic slit-jet expansion have been recorded by exciting the nitrous oxide (N2O) fundamental band ( 2224 cm-1) using a quantum cascade laser. High-resolution infrared spectra of the weakly bound N2O – (C2H2)2 trimer were fitted to a semi-rigid asymmetric rotor Hamiltonian. The band is an a/b-type hybrid band with the rotational constants of A = 87 ) MHz, B = 0 67 0) MHz and C = 8 6 6 ) MHz, satisfying the planarity condition. In addition to the normal istopologue, 15N2O – (C2H2)2 and N2O – (C2D2)2 have been also observed to corroborate the determination of the structure.
A cluster calculation program was used to perform semi-empirical calculations on N2O – (C2H2)2 trimer by using the well-known Muenter’s distributed multipole potentials and Powell minimization method. .According to these calculations, N2O – (C2H2)2 trimer should have a planar structure at the lowest energy minimum which agrees fairly well with the experimental structure.
The two angles between the acetylene and nitrous oxide could not be determined based on the experimental results. The inability to determine these angles may be attributable to the large amplitude motion between the C2H2 monomers, which has been observed in C2H2 dimer, C2D2 dimer and OCS – (C2H2)2. The tunneling motion causes the splitting of energy levels. In the spectrum of N2O – (C2H2)2 trimer, no splittings within the resolution of the experiment (75 MHz) are observed that can be attributed to the large amplitude motion between the C2H2 monomers.