Citation:
Abstract:
This paper presents a high-resolution Fourier transform infrared study of the first CO-stretch overtone band of13CH3OH. The spectrum has been recorded at the Justus-Liebig University, Gießen, Germany on their Bruker IFS 120HR Fourier transform spectrometer. We have assigned parallel subbands in the torsional state n 0 for K values up to6. Each individual subband has been fitted to a J(J / 1) power series expansion in order to obtain the subband originand the state-specific energy expansion coefficients for the first CO-stretch overtone state. The average rotational constantB in the CO-stretch £CO 2 state was found to be 0.768 cm01 , forming a smooth series with that of 0.777 cm01 obtainedin the £CO 1 state and the ground state value of 0.787 cm01 . Modeling of the excited state torsion–vibration energylevel structure derived from the subband origins is then discussed and molecular parameters in the £CO 2 state areproposed. The value obtained for the barrier height to internal rotation is 377.06 { 0.52 cm01 , nearly indistinguishablefrom the value 378.65 cm01 reported for the CO-stretch £CO 1 state. The vibrational energy is found to be 2020.9 {1.4 cm01 . The harmonic wavenumber for the CO-stretch vibration in 13CH3OH was calculated to be v 1029.9 cm01 .The anharmonicity constant of this vibration is vx 6.5 cm01 , giving x 6.3 1 1003 . We have also observedasymmetry-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 3A doublet, where the observed splitting is about 18% larger than that for the ground and COstretch£CO 1 states. 1998 Academic Press