a) Stacked spectrum of all data taken in the frequency range between 87.2 and 90.8 GHz. The red dashed line denotes the 3σ value average over the entire baseline. The HCN and HCO⁺ lines are not shown up to their maximum peak temperature. b) Stacked spectrum of the wobbler switched data taken in the frequency range between 108.1 and 115.5 GHz. The average 3σ value is shown as red dashed line. The baseline noise increases with frequency because of the increasing atmospheric opacity. C¹⁸O, C¹⁷O, and CN are marked but not detected. The ¹²CO and ¹³CO lines are not shown up to their maximum peak temperature.