Observation of mixed acetylene – Nitrous oxide trimers: Infrared spectra of C2H2–(N2O)2 and (C2H2)2–N2O

Abstract

Infrared spectra of the lowest energy isomers of C2H2–(N2O)2 and (C2H2)2–N2O were observed in the region of the ν1 fundamental band of the N2O monomer (∼2224cm−1) using a tunable diode laser and/or a CW quantum cascade laser to probe a pulsed supersonic slit jet expansion. One infrared band was measured for each trimer. The band for C2H2–(N2O)2 corresponds to the out-of-phase vibrations of the pair of equivalent N2O monomers. It is blue shifted by about 10cm−1with respect to the free N2O monomer. The band for (C2H2)2–N2O is slightly less blue shifted (centered at 2232.81cm−1). It can be simulated as a predominately a-type band. In addition to the normal isotopologues,the corresponding bands for C2D2–(N2O)2 and (C2D2)2–N2Owere also observed. The structures of these trimers are similar to those of the lowest energy isomers of the analogous OCS – acetylene trimers reported previously, that is, a twisted barrel with C2 symmetry for C2H2–(N2O)2 and a distorted T-shaped acetylene dimer with a coplanar N2O beside the stem of the T for (C2H2)2–N2O. Here, we present our observation and experimental results, which agree well with calculations based on distributed multipole pair potentials.