84-GHz methanol masers, their relationship to 36-GHz methanol masers and
  their molecular environments
  We present observations of the 36- (4_-1 -> 3_0E) and 84-GHz (5_-1 -> 4_0 E)
class I methanol maser transitions towards a sample of 94 known class I sites.
These observations resulted in 93 and 92 detections in the 84- and 36-GHz
transitions. While the majority of the 36-GHz sources have been previously
reported, many of the sites are observed in the 84-GHz transition for the first
time. The near-simultaneous observations of the two transitions revealed
strikingly similar spectral profiles and a mean and median 36- to 84-GHz
integrated flux density ratio of 2.6 and 1.4.
  Alongside the 36- and 84-GHz observations, we included rare class II methanol
masers at 37.7-, 38.3-, 38.5-, 86.6- and 86.9-GHz, a number of recombination
lines, and thermal molecular transitions. We detect one new site of 86.6- and
86.9-GHz methanol masers, as well as six maser candidates in one or more of
37.7-, 38.3-, 38.5-, 86.6- and 86.9-GHz methanol maser transitions.
  We detect a relatively higher rate of HC3N compared to that reported by
MALT90 (once the respective detection limits were taken into account) who
targeted dense dust clumps, suggesting that the class I methanol maser targets
incorporate a relatively higher number of warm protostellar sources. We further
find that there are similar relationships between the integrated flux density
of both class I transitions with the integrated intensity of HC3N, HNC, HCO+,
HNC, SiO and H13CO+. We suggest that this indicates that the integrated flux
density of the 36- and 84-GHz transitions are closely linked to the available
gas volume.
