ARE CLOUDS COLLAPSING AT THE 2'-NORTH POSITION OF SAGITTARIUS B2

The 3 mm lines of HCO2+ and HNCO have been observed toward Sgr B2. Bes ides the well-known ''principal cloud'' and an extended envelope, we f ind another gas cloud 2' north of Sgr B2(M). This 2' north (2' N) clou d which may be located behind the principal cloud, has a total mass of similar to 10(5) M-. and a diameter of similar to 7 pc. HCO2+ and HNC O exist mainly at 2' north, and their column densities are about 2.2 x 10(14) and 2.3 x 10(15) cm(-2) respectively. The fractional abundance s of these species relative to molecular hydrogen appear to bd enhance d by at least a factor of 10 compared to the principal cloud. We have also identified redshifted and blueshifted high-velocity components wh ich move toward the 2' N position with projected velocities of +/-30 k m s(-1). These components are located symmetrically around 2' N, along the Galactic plane, and have diameters of about 4-5 pc and masses of similar to 1 x 10(4) M-.. The flow energies are large enough to initia te new star formation in the 2'N region on the free-fall timescale of 10(5) yr. This large-scale collapsing motion may cause a strong shock in the 2' N cloud and result in the enhancement of HCO2+ and HNCO.