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A study was conducted to analyze the assignment and structural analysis of the argon-cyclobutanone (CBO) van der Waals complex determined with a pulsed-jet Fourier transform microwave spectrometer. A pulsed jet of gas supporting a low rotational temperature was generated by a conventional pulsed supersonic expansion. Results indicated transitions of 13C substitutions at carbon positions of the CBO ring.

The rotational spectra of cyclopentanone and its van der Waals complexes with argon and neon have been observed with a Balle-Flygare type pulsed jet Fourier transform microwave spectrometer in the 6 to 20 GHz region. This work improves the rotational constants and quartic centrifugal distortion constants for cyclopentanone and its five (13)C and the (18)O isotopologues. The argon-(12)C5H8(16)O van der Waals complex has rotational constants of A = 2611.6688, B = 1112.30298, and C = 971.31969 MHz. The (20)Ne-(12)C5H8(16)O complex has rotational constants of A = 2728.8120, B = 1736.5882, and C = 1440.4681 MHz. In addition, the five unique, singly substituted (13)C and (18)O isotopologues of the argon complex are reported. The five single-substituted (13)C of the (20)Ne complex and the (22)Ne-(12)C5H8(16)O complex are reported. The rare gases are in van der Waals contact with the carbonyl α carbon and nearly in contact with the hydrogen on β and γ carbons toward the back of the ring.

The rotational spectra of cyclohexene oxide and its van der Waals complex with argon have been observed with a Balle-Flygare type pulsed jet Fourier transform microwave spectrometer in the 6 to 20 GHz region. This work improves the existing rotational and quartic centrifugal distortion constants of cyclohexene oxide, its six singly substituted (13)C, and the (18)O isotopologue. In addition, the (17)O isotopologue was observed in natural abundance. The quadrupole coupling constants for the (17)O isotopologue are χ(aa) = 8.855(5), χ(bb) = -4.560(4), and χ(cc) = -4.296(4) MHz. The argon-(12)C6H10(16)O complex has rotational constants of A = 2146.4825(2), B = 908.64292(8), and C = 859.00320(8) MHz. Additionally, the six unique singly substituted (13)C isotopologues of the argon complex are reported here. The position of the argon that is consistent with the parent and six (13)C complex rotational constants is above the ring on the side opposite the epoxide.

Rotational spectra for hexafluoroisobutene, and its (13)C isotopologues, have been recorded between 8 and 16 GHz using a chirped pulse, Fourier transform microwave spectrometer. Notably, all spectra observed are doubled with separations between the doublets being between 1 and 60 MHz. We propose that the bis-trifluoromethyl groups of the target molecule are staggered in the equilibrium configuration, and that a novel, out-of-phase rotation through a F-CCC-F planar configuration with low barrier (<100 cm(-1)), leads to the observed doubled rotational spectra.

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 (13)C and (18)O 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 (13)C and (18)O isotopes. For the argon cyclopentene oxide complex, both a and b-type transitions were observed and the rotational constants for the all-(12)C (16)O isotopologue were determined to be A = 3268.254(2), B = 993.345(1), and C = 950.430(9) MHz. The r(0) 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 from the oxygen and is 0.42 A off to the side and 0.27 A from the center of mass toward the back end of the ring (again away from the oxygen). Large amplitude van der Waals bending vibrations require an averaging model to account for differences between the observed complex and monomer planar moments of inertia.

The rotational spectrum of the argon-tropolone van der Waals complex in the ground vibrational state has been measured in the frequency range of 6-17 GHz using a pulsed-jet, Balle-Flygare-type Fourier transform microwave spectrometer. Eighty-six transitions for the complex (Ar-(12)C(7)H(6)(16)O(2)) were observed, assigned, and fit using a Watson A-reduction Hamiltonian giving the rotational and centrifugal distortion constants A = 1080.4365(3) MHz, B = 883.4943(3) MHz, C = 749.0571(2) MHz, Delta(J) = 2.591(2) kHz, Delta(JK) = -3.32(1) kHz, Delta(K) = 5.232(9) kHz, delta(J) = 0.944(1) kHz, and delta(K) = -0.028(8) kHz. The tunneling motion of the hydroxyl proton in the tropolone moiety is quenched in the ground electronic state by complexation with argon. The coordinates of the argon atom in the monomer's principal axis system are a = 0.43 A, b = 0.23 A, and c = 3.48 A.