Fourier Transform Infrared Spectroscopy of the First CO-Stretch Overtone Band of13CH3OH

✍ Scribed by Adriana Predoi-Cross; G.C. Mellau; R.M. Lees; B.P. Winnewisser

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 362 KB
• Volume: 189
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1998.7552

✦ Synopsis

This paper presents a high-resolution Fourier transform infrared study of the first CO-stretch overtone band of 13 CH 3 OH. The spectrum has been recorded at the Justus-Liebig University, Gießen, Germany on their Bruker IFS 120 HR Fourier transform spectrometer. We have assigned parallel subbands in the torsional state n Å 0 for K values up to 6. Each individual subband has been fitted to a J(J / 1) power series expansion in order to obtain the subband origin and the state-specific energy expansion coefficients for the first CO-stretch overtone state. The average rotational constant B in the CO-stretch £ CO Å 2 state was found to be 0.768 cm 01 , forming a smooth series with that of 0.777 cm 01 obtained in the £ CO Å 1 state and the ground state value of 0.787 cm 01 . Modeling of the excited state torsion-vibration energy level structure derived from the subband origins is then discussed and molecular parameters in the £ CO Å 2 state are proposed. The value obtained for the barrier height to internal rotation is 377.06 { 0.52 cm 01 , nearly indistinguishable from the value 378.65 cm 01 reported for the CO-stretch £ CO Å 1 state. The vibrational energy is found to be 2020.9 { 1.4 cm 01 . The harmonic wavenumber for the CO-stretch vibration in 13 CH 3 OH was calculated to be v Å 1029.9 cm 01 . The anharmonicity constant of this vibration is vx Å 6.5 cm 01 , giving x Å 6.3 1 10 03 . We have also observed asymmetry-induced K doubling for the subbands of A symmetry for K values from 1 to 3 at sufficiently high J values. The size of the splitting coefficients is similar to those observed for the CO-stretch fundamental ( 14), with the exception of those for the K Å 3A doublet, where the observed splitting is about 18% larger than that for the ground and COstretch £ CO Å 1 states.