Position-velocity plots along the direction with PA = 68° toward the HMC of panel a: CH₃CN K = 2, panel b: CH₃¹³CN K = 2, panel c: CH₃CN K = 8, and panel d: CH₃CN K, l = (6, 1) v₈ = 1 (12–11). The offsets are measured from the phase center, positive to the northeast. Contour levels range from 20 to 180 mJy beam⁻¹ in steps of 20mJy beam⁻¹. The vertical dashed white line indicates the position of the continuum peak, while the vertical solid black lines show the position of the two compact free-free continuum sources detected by Cesaroni et al. (2010). The horizontal dashed line indicates the systemic LSR velocity. The error bars in the lower left-hand corner of the panels indicate the angular and spectral resolution of the data. The upper level energies E_up of each transition are indicated in the lower right-hand corner of the panels.