Related Experiment Video
Updated: Jul 27, 2026

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
Published on: August 18, 2017
The Forbidden Rotational Q-Branch of CH3CF3: Torsional Properties and (A1 - A2) Splittings
Ozier1, Schroderus, Wang
1Laboratorium für Physikalische Chemie, Eidgenössische Technische Hochschule, Zürich, CH-8092, Switzerland
Abstract:
The pure rotational spectrum driven by the small distortion dipole moment perpendicular to the symmetry axis has been investigated between 8 and 18 GHz for CH3CF3 in the ground vibrational state using a pulsed Fourier transform waveguide spectrometer. This molecule has been selected as a prototype for the case of a symmetric top with small ( approximately 500 kHz) torsional energy splittings in the ground torsional state (nu6 = 0). In this state, six (k +/- 3 <-- k) Q-branch series have been measured for lower state K = |k| between 3 and 8 with 27 = J = 75. For (nu6 = 1), three series with lower state K between 5 and 7 with 49 = J = 66 have been observed. In two of these series, the torsional fine structure extending over approximately 6.8 MHz has been fully resolved. The (A1 - A2) splitting has been measured in the (nu6 = 0) series (K = 6 <-- 3) for 37 = J = 74. The global data set of 443 frequencies included avoided-crossing molecular-beam splittings of Meerts and Ozier (1991. Chem. Phys. 152, 241-259) and mm-wave R-branch measurements of Bocquet et al. (1994. J. Mol. Spectrosc. 165, 494-499). In a weighted least-squares analysis, a good fit was obtained by varying 18 parameters in a Hamiltonian that represented both the torsional effects and the sextic splittings. Effective values have been determined for both rotational constants, eight torsional parameters including the barrier height, six diagonal centrifugal distortion constants, and two centrifugal distortion constants (epsilon and epsilonJ) that characterize the (Deltak = +/-3) matrix elements. The difficulties are discussed that arise in defining a unique model for the torsional terms in the Hamiltonian when a high barrier symmetric top is investigated by distortion moment spectroscopy. The redundancies are investigated that exist in the quartic and sextic Hamiltonian for a near-spherical top such as CH3CF3. Copyright 1998 Academic Press.
Related Concept Videos
Conformations of Cyclohexane
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
Chair Conformation of Cyclohexane
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
¹H NMR: Complex Splitting
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
NMR Spectroscopy of Benzene Derivatives
Radicals: Electronic Structure and Geometry
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...

