Fourier transform spectroscopy of the CO-stretching band of C-13 methanol in the torsional ground state

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Abstract
The Fourier transform spectrum of the CO-stretching fundamental band of 13CH3OH has been investigated at 0.002 cm−1 resolution. For the n=0 torsional ground state, 35 subbands containing some 2300 lines have been identified for K values from 0 to 10 for the three torsional symmetries A, E1, and E2 up to J values typically well over 30. The assigned transitions have been fitted to J(J+1) power-series expansions to obtain subband origins and sets of phenomenological state-specific parameters describing the J dependence of the subbands. These parameters reproduce the observed wave numbers to within the experimental uncertainty of ±0.0005 cm−1 for unblended lines, except when particularly large asymmetry shifts or perturbations due to Fermi or Coriolis resonances are present. The subband origins have been fitted to effective molecular constants for the excited CO-stretching state and a torsional barrier of 378.7(8) cm−1 is found, representing a 1.3% increase over the ground state value. A wide variety of global or J-localized perturbations has been seen, and most of the interacting states have been identified. New assignments have been obtained for far-infrared laser lines optically pumped by the 10R(2) and 9P(12) CO2 laser lines.