  Aims. Infrared dark clouds represent the earliest stages of high-mass star
formation. Detailed observations of their physical conditions on all physical
scales are required to improve our understanding of their role in fueling star
formation.
  Methods. We investigate the large-scale structure of the IRDC G035.39-00.33,
probing the dense gas with the classical ammonia thermometer. This allows us to
put reliable constraints on the temperature of the extended, pc-scale dense gas
reservoir and to probe the magnitude of its non-thermal motions. Available
far-infrared observations can be used in tandem with the observed ammonia
emission to estimate the total gas mass contained in G035.39-00.33.
  Results. We identify a main velocity component as a prominent filament,
manifested as an ammonia emission intensity ridge spanning more than 6 pc,
consistent with the previous studies on the Northern part of the cloud. A
number of additional line-of-sight components are found, and a large scale,
linear velocity gradient of ~0.2 km s$^{-1}$ pc$^{-1}$ is found along the ridge
of the IRDC. In contrast to the dust temperature map, an ammonia-derived
kinetic temperature map, presented for the entirety of the cloud, reveals local
temperature enhancements towards the massive protostellar cores. We show that
without properly accounting for the line of sight contamination, the dust
temperature is 2-3 K larger than the gas temperature measured with NH$_3$.
  Conclusions. While both the large scale kinematics and temperature structure
are consistent with that of starless dark filaments, the kinetic gas
temperature profile on smaller scales is suggestive of tracing the heating
mechanism coincident with the locations of massive protostellar cores.
