We present 247-GHz molecular line observations of methanol ( CH _ { 3 } OH ) toward sixteen massive star-forming regions , using the APEX telescope with an angular resolution of 25 ^ { \prime \prime } .
The sample covers a range of evolutionary states , including warm molecular cores , hot molecular cores , and ultracompact HII regions .
The hot cores , all of which include UC HII regions , show rich molecular line spectra , although the strength of different species and transitions varies from source to source .
In contrast , the warm cores do not show significant molecular line emission .
Multiple methanol transitions are detected toward nine of the hot cores ; eight of these had enough transitions to use the rotation diagram method to estimate rotational temperatures and column densities .
The temperatures lie in the range 104–168 K and column densities from 3 \times 10 ^ { 16 } to 7 \times 10 ^ { 18 } cm ^ { -2 } .
Using the average methanol line parameters , we estimate virial masses , which fall in the range from 145 to 720 M _ { \odot } and proved to be significantly higher than the measured gas masses .
We discuss possible scenarios to explain the chemical differences between hot cores and warm molecular cores .
One of the observed methanol lines , 4 _ { 2 } -5 _ { 1 } A ^ { + } at 247.228 GHz , is predicted to show class II maser emission , similar in intensity to previously reported J _ { 0 } - J _ { -1 } E masers at 157 GHz .
We did not find any clear evidence for maser emission among the observed sources ; however , a weak maser in this line may exist in G345.01+1.79 .