Search

Vinylsulfur pentafluoride (VSPF), a molecule with a four-fold internal rotor, —SF4, has been studied with high resolution Fourier transform microwave spectroscopy. We believe that this is the first report of resolved four-fold internal rotation. As such, we have presented the tools needed to understand and analyze such a problem. These include debugging the ERHAM computer program necessary to fit the spectra and the free rotor to high barrier correlation diagram necessary to understand the torsional states of the four-fold rotor. The A, E, and B torsional state rotational transitions are well resolved and assigned. Spectroscopic transitions of four isotopologues of VSPF, H2C=CH—SF5, the normal isotopologue, and the singly substituted 34S and 13C isotopologues were measured and assigned. Contrary to expectation, the A torsional state could not be fit with only a semi-rigid Hamiltonian. The barrier to internal rotation, V4, is found to be 227 cm−1. Ab initio calculations at the MP2 aug-cc-pVQZ level of theory and basis set were performed and the results of this calculation are compared to our experimental results. [ABSTRACT FROM AUTHOR]

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.

Rotationally resolved microwave (MW) and ultraviolet (UV) spectra of jet-cooled tropolone have been obtained in S0 and S1 electronic states using Fourier-transform microwave and UV-laser/molecular-beam spectrometers. In the ground electronic state, the MW spectra of all heavy-atom isotopomers including one 18O and four 13C isotopomers were observed in natural abundance. The OD isotopomer was obtained from isotopically enriched samples. The two lowest tunneling states of each isotopomer except 18O have been assigned. The observed inversion splitting for the OD isotopomer is 1523.227(5) MHz. For the asymmetric 13C structures, the magnitudes of tunneling-rotation interactions are found to diminish with decreasing distance between the heavy atom and the tunneling proton. In the limit of closest approach, the 0+ state of 18O was well fitted to an asymmetric rotor Hamiltonian, reflecting significant changes in the tautomerization dynamics. Comparisons of the substituted atom coordinates with theoretical predictions at the MP2/aug-cc-pVTZ level of theory suggest the localized 0+ and 0- wave functions of the heavier isotopes favor the C-OH and C=O forms of tropolone, respectively. The only exception occurs for the 13C-OH and 13C=O structures which correlate to the 0- and 0+ states, respectively. These preferences reflect kinetic isotope effects as quantitatively verified by the calculated zero-point energy differences between members of the asymmetric atom pairs. From rotationally resolved data of the 0+←0+ and 0-←0- bands in S1, line-shape fits have yielded Lorentzian linewidths that differ by 12.2(16) MHz over the 19.88(4) cm-1 interval in S1. The fluorescence decay rates together with previously reported quantum yield data give nonradiative decay rates of 7.7(5)×108 and 8.5(5)×108 s-1 for the 0+ and 0- levels of the S1 state of tropolone. [ABSTRACT FROM AUTHOR]

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.