Analysis of the rovibrational spectrum of 13CH4 in the Octad range

We have measured the infrared spectrum of methane (CH4)-C-13 from 1100 cm(-1) (33 THz), below the fundamental range, to about 12000 cm(-1) (360 THz) in the high overtone region at temperatures ranging from 80 K to 300 K by high resolution Fourier transform infrared (FTIR) spectroscopy. With instrumental bandwidths between 0.0027 cm(-1) (80 MHz) and 0.01 cm(-1) (300 MHz) this provides close to Doppler-limited spectra, using the Zurich prototype spectrometer (ZP2001, Bruker 125HR) combined with a multipath collisional cooling cell. Using perturbation theory and an accurate empirically adjusted potential we have computed ro-vibrational energy levels of (CH4)-C-13 and (CH4)-C-12 in the same energy range. Exploiting the synergy between theory and experiment, we analyze here specifically the experimental spectra in the Octad range (similar to 3700-4700 cm(-1), or 110 to 140 THz), using the theoretical results to guide the fitting of parameters of a Dijon effective Hamiltonian theory. With the aid of the theoretical results it is possible to analyse the Octad of (CH4)-C-13 with much less effort than without such information. In the end 1144 purely experimental line positions were fitted with root mean square deviations d(rms) <= 2.6 x 10(-3) cm(-1) (5548 data including theoretical results, with similar d(rms)). (C) 2013 Elsevier Inc. All rights reserved.