The properties of tidally induced arms provide a means to study molecular cloud formation and the subsequent star formation under environmental conditions which in principle are different from quasi stationary spiral arms . We report the properties of a newly discovered molecular gas arm of likely tidal origin at the south of NGC 4039 and the overlap region in the Antennae galaxies , with a resolution of 1 \farcs 68 \times 0 \farcs 85 , using the Atacama Large Millimeter/submillimeter Array science verification CO ( 2–1 ) data . The arm extends 3.4 kpc ( 34″ ) and is characterized by widths of \lesssim 200 pc ( 2″ ) and velocity widths of typically \Delta V \simeq 10–20 km s ^ { -1 } . About 10 clumps are strung out along this structure , most of them unresolved , with average surface densities of \Sigma _ { gas } \simeq 10–100 M _ { \odot } pc ^ { -2 } , and masses of ( 1–8 ) \times 10 ^ { 6 } M _ { \odot } . These structures resemble the morphology of beads on a string , with an almost equidistant separation between the beads of about 350 pc , which may represent a characteristic separation scale for giant molecular associations . We find that the star formation efficiency at a resolution of 6″ ( 600 pc ) is in general a factor of 10 higher than in disk galaxies and other tidal arms and bridges . This arm is linked , based on the distribution and kinematics , to the base of the western spiral arm of NGC 4039 , but its morphology is different to that predicted by high-resolution simulations of the Antennae galaxies .