W49N is a mini-starburst in the Milky Way and thus an ideal laboratory for high-mass star formation studies .
Due to its large distance ( 11.1 _ { -0.7 } ^ { +0.9 } kpc ) , the kinematics inside and between the dense molecular clumps in W49N are far from well understood .
The SMA observations resolved the continuum emission into two clumps .
The molecular line observation of SO _ { 2 } ( 28 _ { 4 , 24 } -28 _ { 3 , 25 } ) suggests that the two clumps have a velocity difference of \sim 7 km s ^ { -1 } .
The eastern clump is very close to two radio sources “ G1 ” and “ G2 ” , and the western clump coincides with a radio source “ B ” .
The HCN ( 3-2 ) line reveals an extremely energetic outflow , which is among the most energetic molecular outflows in the Milky Way .
This is the first report of high-velocity molecular outflow detection in W49N .
The outflow jet might be in precession , which could account for the distribution , velocity and rotation of water maser spots .
Three absorption systems are identified in HCO ^ { + } ( 3-2 ) spectra .
The absorption features are blueshifted with respect to the emission of SO _ { 2 } ( 28 _ { 4 , 24 } -28 _ { 3 , 25 } ) lines , indicating that a cold layer is expanding in front of the warm gas .
Further analysis indicates that the expansion is decelerated from the geometric expansion centers .