Spectra of ethylene dimers and trimers are studied in the nu11 and (for the dimer) nu9 fundamental band regions of C2H4 (~2990 and 3100 cm-1) using a tunable optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. The deuterated trimer has been observed previously, but this represents the first rotationally resolved spectrum of (C2H4)3. The results support the previously determined cross-shaped (D2d) dimer and barrel-shaped (C3h or C3) trimer structures. However, the dimer spectrum in the nu9 fundamental region of C2H4 is apparently very perturbed and a previous rotational analysis is not well verified.
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