Comparison of the synthetic spectra based on the MARCS models with the observed VISIR spectra of seven K–M giants. The observed and synthetic spectra are shown by the black and red solid lines, respectively. The relatively isolated ²⁸SiO, ²⁹SiO, and ³⁰SiO lines are marked by the black, red, and green arrows, respectively. See Fig. 1 for their identification. The ²⁸SiO lines with absorption excess are marked by the blue dots.