Application of Permutation–Inversion Group Theory to the Interpretation of the Microwave Absorption Spectrum of Dimethyl Methylphosphonate

Grabow

2008

Chemical Physics

The microwave spectra of (CH 3 ) 3 74 Ge 79 Br and its isotopologues (CH 3 ) 3 72 Ge 79 Br and (CH 3 ) 3 74 Ge 81 Br have been studied in the frequency range from 2.4-20 GHz revealing the complex internal dynamics of this organometallic molecule with three internal rotors. The assignment of the complex spectrum has been facilitated by permutation-inversion theory -the appropriate molecular symmetry group is G 162 . The V 3 barrier to internal rotation is determined to be 4.783(12) kJ/mol. An analysis of the bromine quadrupole coupling yields the description of the Ge-Br and the Ge-C bonding characters. From this analysis we find that the bromine atom has a positive partial charge resulting from π-backbonding of the bromine towards germanium. From isotopic substitution, the Ge-Br bond distance could be determined to 2.34589(21) Å.

Section: High-barrier Tunneling-rotation Formalismmentioning

confidence: 99%

Three-dimensional intramolecular dynamics: Internal rotation of (CH3)3GeBr

Grabow

2008

Chemical Physics

“…To determine the relative ordering and to facilitate an assignment of the torsional transitions observed in the spectrum we used the high-barrier group-theoretical tunneling-rotation formalism [20] appropriate for G 162 , based on the coordinates and their transformation properties defined above, to predict the torsional splitting pattern for K = 0. For a C 3v -symmetric molecule with three group-theoretically equivalent internal rotors such as (CH 3 ) 3 SnCl, n = 27 different frameworks are present.…”

Section: High-barrier Tunneling-rotation Formalismmentioning

confidence: 99%

Towards the complete analysis of the rotational spectrum of (CH3)3SnCl

Journal of Molecular Spectroscopy

Hougen

Grabow

2008

Self Cite

The rotational spectrum of the symmetric top trimethyl tin chloride (CH 3 ) 3 SnCl has been studied using a pulsed molecular beam Fourier transform microwave spectrometer in the frequency range from 3 to 24 GHz. The spectrum is exceedingly complicated by the internal rotation motions of the three equivalent methyl tops, the high number of Sn-and Cl-isotopes and the quadrupole hyperfine structure of the chlorine nucleus. In this paper, we present the microwave spectrum, ab initio calculations, permutation inversion (PI) group-theoretical considerations, Starkeffect measurements and finally the assignments and fits of the different torsionrotation species. Based on the Stark-effect measurements, the dipole moment is µ = 3.4980(30) D. Due to ∆K = ±1-mixing effects we observe linear Stark-effect behavior and additional quadrupole splitting for some K = 0 torsion-rotation transitions in (CH 3 ) 3 SnCl, which can be group-theoretically explained. The symmetric rotor fit of A 1 states leads to an effective B-constant of 1680.040124(50) MHz for the main isotopologue (CH 3 ) 3 120 Sn 35 Cl. A global fit of 182 K = 0 torsion-rotation transitions yields a V 3 torsional barrier of 148.299(54) cm −1 .

“…Using this multidimensional high-barrier tunneling-rotation formalism [49] appropriate for G 162 , based on the coordinates and their transformation properties defined above, the torsional splitting pattern for K = 0 can be predicted. In the high-barrier tunneling-rotation formalism it is necessary to assume that (CH 3 ) 3 SnCl spends most of its time vibrating in the vicinity of one of these 27 frameworks and only occasionally tunnels from one conformation to another.…”

Section: High-barrier Tunneling-rotation Formalism and Local-mode Trementioning

confidence: 99%

Understanding High‐Resolution Spectra of Nonrigid Molecules Using Group Theory

2010

ChemPhysChem

Permutation-inversion group theory has developed to become an important tool in the high-resolution spectroscopy of nonrigid molecules. This large class of molecules is very intriguing to study. Small molecules such as ammonia or Na(3) are known to be nonrigid. With increasing size, however, several large-amplitude motions are possible in a molecule, and can even interact with each other. The high-resolution spectra of nonrigid molecules are known to be quite complicated and very rich in information. Details about the molecule and its internal dynamics can be extracted, such as the molecular structure, the character of the chemical bonds, and the barrier heights to internal rotation and their dependence on the chemical bonds. However, due to the nonrigidity of the molecule and the complexity of such spectra, their analysis is usually quite challenging. Theoretical methods are needed for their prediction and analysis. This Review concentrates on permutation-inversion group theory and its usefulness for the analysis of high-resolution spectra of nonrigid molecules, which is examined in more detail using different examples. In a separate section, a special aspect of molecular symmetry is discussed: the breakdown of symmetry principles. Special emphasis is placed on the breakdown of space inversion symmetry (parity violation) in chiral molecules and its possible implications in high-resolution spectroscopy.