Alignment in velocity space of unidentified emission at ~354.2 GHz (top) with known maser emission (bottom). The spectra shown in the top panels, from left to right, assume rest frequencies of 354.1948, 354.2000, and 354.2022 GHz, respectively. The bottom panels show, from left to right, H₂ O (–2_2,0) at 183.3 GHz, SiO (v = 3, J = 4–3) at 170.1 GHz, and SiO (v = 1, J = 7–6) at 301.8 GHz. Vertical dashed lines indicate emission components similar to those mentioned in the discussion in Sect. 3.