Analysis of the interacting Octad system of 12CH4

The octad system of methane (CH4)-C-12 has been analyzed with a fourth-order (459 parameters) Hamiltonian for energy levels and a third-order (28 parameters) dipole moment expansion for infrared intensities. Nearly 8000 assigned positions and 2500 measured line intensities (obtained with the Fourier transform spectrometer located at Kitt Peak National Observatory/National Solar Observatory) have been considered in the modeling. Infrared (Octad-Ground State) and hot bands (Octad-Dyad) data have been used, While the model does not reproduce the measurements at their inherent experimental precisions, it has been sufficient to interpret and substantially assign this spectral region of methane for the first time in over 30 years of investigation, (C) 2001 Academic Press.