Determination of the structure of cyclopentene oxide and the argon-cyclopentene oxide van der Waals complex.

Rotational spectra of cyclopentene oxide and the argon−cyclopentene oxide van der Waals complex were studied using pulsed-jet Fabry−Perot Fourier transform microwave (FTMW) spectroscopy. Spectra of the parent along with those of the 13C and 18O singly substituted isotopologues, in natural abundance, of the monomer and of the complex were measured in the frequency region of 5−26.5 GHz. The complete heavy atom substitution structure was determined for the monomer and complex. The boat structure for cyclopentene oxide was confirmed with naturally abundant 13C and 18O isotopes. For the argon cyclopentene oxide complex, both a and b-type transitions were observed and the rotational constants for the all-12C 16O isotopologue were determined to be A = 3268.254(2), B = 993.345(1), and C = 950.430(9) MHz. The r0 coordinates of the argon in the principal axis system of cyclopentene oxide are a = 0.27, b = 0.42, and c = 3.91 A, such that the argon is exo to the boat of the ring and on the opposite side of the ring f...