The ''Ritz'' program has been used for the investigation of the absorption spectrum of the (CH3OH)-C-13-O-16 isotopomer of methanol from 25 to 350 cm(-1). This allowed us to assign some perturbed level sequences which could not be followed by the Taylor expansions used in a previous program. Altogether, more than 13 800 lines have been assigned in the investigated region, and the energies of 1363 levels of A symmetry and 2006 levels of E symmetry have been evaluated. A comparison with the energy level values of the parent species (CH3OH)-C-12 is presented. Some forbidden transitions, due to state mixings, have been observed. Taylor expansion coefficients for evaluating the energies of the levels involved in the transitions are also given. All of the lines presented in this paper correspond to transitions involving torsionally excited levels within the ground vibrational state. (C) 1995 Academic Press, Inc.1741177195