  We present Atacama Large Millimeter/submillimeter Array observations of a
radio-loud and millimeter-bright galaxy at z=2.6. Gravitational lensing by a
foreground galaxy at z~0.2 provides access to physical scales of approximately
360 pc, and we resolve a 2.5 kpc-radius ring of star-forming molecular gas,
traced by atomic carbon CI(1-0) and carbon monoxide CO(4-3). We also detect
emission from the cyanide radical, CN(4-3). With a velocity width of 680 km/s,
this traces dense molecular gas travelling at velocities nearly a factor of two
larger than the rotation speed of the molecular ring. While this could indicate
the presence of a dynamical and photochemical interaction between the active
galactic nucleus and molecular interstellar medium on scales of a few 100 pc,
on-going feedback is unlikely to have a significant impact on the assembly of
stellar mass in the molecular ring, given the ~10s Myr depletion timescale due
to star formation.
