The Microwave Spectrum of m-Tolunitrile: Methyl Internal Rotation and 14N Nuclear Quadrupole Coupling

✍ Scribed by T. Bruhn; H. Mäder

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 224 KB
• Volume: 200
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1999.8043

✦ Synopsis

The microwave spectrum of m-tolunitrile (3-methylbenzonitrile, m-C 6 H 4 CH 3 CN) has been investigated in the frequency range from 1 to 4 and 8 to 26.5 GHz. The spectra in the two lowest states of internal methyl rotation (m ϭ 0, Ϯ1) were recorded by means of pulsed molecular beam Fourier transform microwave (MB-FTMW) spectrometers. The interpretation of the spectra was based on an asymmetric frame-symmetric top Hamiltonian with inclusion of centrifugal distortion terms and first-order contributions from 14 N nuclear quadrupole coupling. A least-squares analysis yielded the rotational constants A ϭ 3295.9103(10) MHz, B ϭ 1199.1188(2) MHz, C ϭ 883.9223(1) MHz, all elements of the nuclear quadrupole coupling tensor aa ϭ Ϫ3.626(1) MHz, bb ϭ 1.684(1) MHz, cc ϭ 1.943(1) MHz, and ab ϭ Ϫ1.870(3) MHz, as well as the threefold barrier to internal rotation, V 3 ϭ 14.2 cm Ϫ1 , and the angle between the internal rotor axis and the principal moment of inertia a axis, ϭ 42.66°, using fixed values for the sixfold barrier term V 6 (Ϫ11 cm Ϫ1 ) and the moment of inertia of the methyl top I ␣ (3.16 u Å 2 ).