New assignments, line intensities, and HITRAN database for CH3OH at 10 μm

Abstract The Fourier transform spectrum of CH 3 OH in the 10 μm region has been re-examined at higher pressure and path length than heretofore, as part of a program to provide comprehensive CH 3 OH spectral data for astrophysical and atmospheric applications. With the increase in spectral sensitivity, it has been possible to assign new torsionally excited ν 12 =1 and ν 12 =2 subbands plus further high- K , ν 12 =0 subbands of the ν 8 CO-stretching band. Upper-state term values have been determined, and have been fitted to J ( J +1) power-series expansions in order to obtain the excited ν 8 substate origins. A variety of weaker subbands from other modes has also been identified in the 10 μm spectrum including ν 12 =0, ν 12 =1, and ν 12 =0←1 torsional subbands of the ν 7 in-plane CH 3 rock, ν 12 =0←1 and ν 12 =0←2 torsional combination subbands of the ν 6 OH bend, and ν 12 =0←2 subbands of the ν 5 symmetric CH 3 bend. Line intensities have been retrieved line-by-line from the spectra. A large set of “unperturbed” ν 8 transitions has been modeled using the same type of multi-parameter effective Hamiltonian employed successfully for the ground state, with inclusion of the intensities of a subset of the stronger ν 8 spectral lines in the fitting in order to obtain appropriate transition dipole terms. Together, a 10 μm methanol database in HITRAN format has been generated.