High-Resolution Fourier Transform Spectrum of the CO Stretch Band of CH 3OD

Abstract

The Fourier transform spectrum of the infrared CO stretch band of CH 3OD has been recorded in the region 980-1100 cm −1, at a resolution of 0.004 cm −1. More than 1300 absorption lines belonging to ( nτ K) subbands with n = 0, K ranging from 0 to 5, and J from 0 to 34 have been assigned to P-, Q-, and R-branch transitions. The assignments are supported by combination differences obtained from both calculated and previously measured ground state microwave frequencies. The assignments have allowed the determination of expansion coefficients in J( J + 1) power series describing individual subbands. These coefficients allow, for the unperturbed series, spectral wavenumbers to be calculated close to the estimated uncertainty. By making simple approximations, the moments of inertia as well as the barrier height for internal rotation have been determined for the excited state. The latter is found to be 357 cm −1 compared to 366 cm −1 for the ground state. Some of the subbands are observed to be perturbed. One of these perturbations can be associated with a Fermi resonance between the (015) E 1 stack of the excited CO stretch state the torsional excited (415) E 1 stack of the ground state.