We mapped the MSX dark cloud G084.81 - 01.09 in the NH _ { 3 } Â ( 1,1 ) - ( 4,4 ) lines and in the J = 1-0 transitions of ^ { 12 } CO , ^ { 13 } CO , C ^ { 18 } O and HCO ^ { + } in order to study the physical properties of infrared dark clouds , and to better understand the initial conditions for massive star formation .
Six ammonia cores are identified with masses ranging from 60 to 250Â M _ { \sun } , a kinetic temperature of 12Â K , and a molecular hydrogen number density n ( { H _ { 2 } } ) \sim 10 ^ { 5 } Â cm ^ { -3 } .
In our high mass cores , the ammonia line width of 1 km s ^ { -1 } is larger than those found in lower mass cores but narrower than the more evolved massive ones .
We detected self-reversed profiles in HCO ^ { + } across the northern part of our cloud and velocity gradients in different molecules .
These indicate an expanding motion in the outer layer and more complex motions of the clumps more inside our cloud .
We also discuss the millimeter wave continuum from the dust .
These properties indicate that our cloud is a potential site of massive star formation but is still in a very early evolutionary stage .