Data subset of EMIR spectra at 0.9 mm of the O-rich stars IK Tau and OH 231.8+4.2 obtained in January 2011 as part of an on-going mm-wavelength spectral line survey of O-rich evolved stars by Sanchez Contreras et al. (2011). Bottom: selected spectra obtained with WILMA around 300 and 343 GHz. WILMA is a broad band spectrometer of the 30-m telescope of the autocorrelator type. Top: zoom of a smaller frequency range (indicated by vertical dashed lines in the bottom panels) showing higher spectral resolution spectra obtained with fast fourier transform spectrometers (FTS).