Methyl cyanide spectrum obtained with the Plateau de Bure interferometer towards IRAS 20126+4104. The line emission has been integrated over the core. The dotted lines mark the CH₃CN (from top) and CH₃¹³CN (from bottom) transitions. The single numbers denote the K component, while the number pairs correspond to the K,l quantum numbers of the vibrationally excited, v₈ = 1, transitions. We note how most of the CH₃CN and CH₃¹³CN components are blended with other methyl cyanide lines and/or with lines of other species.