We present results of a H13CN J=1-0 mapping survey of molecular clouds toward the Galactic Center (GC) region of -1.6° ≤ l ≤ 2° and -0.23° ≤ b ≤ 0.30° with 2' grid resolution. The H13CN emissions show similar distribution and velocity structures to those of the H12CN emissions, but are found to better trace the feature saturated with H12CN (1-0). The bright components among multi-components of H12CN line profiles usually appear in the H13CN line while most of the dynamically forbidden, weak H12CN components are seldom detected in the H13CN line. We also present results of other complementary observations in 12CO (J=1-0) and 13CO (J=1-0) lines to estimate physical quantities of the GC clouds, such as fractional abundance of HCN isotopes and mass of the GC cloud complexes. We confirm that the GC has very rich chemistry. The overall fractional abundance of H12CN and H13CN relative to H2 in the GC region is found to be significantly higher than those of any other regions, such as star forming region and dark cloud. Especially cloud complexes nearer to the GC tend to have various higher abundance of HCN. Total mass of the HCN molecular clouds within |l|≤ 6° is estimated to be ~2 ×10 7 M⊙ using the abundances of HCN isotopes, which is fairly consistent with previous other estimates. Masses of four main complexes in the GC range from a few 10 5 to ~ 10 7 M⊙ All the HCN spectra with multi-components for the four main cloud complexes were investigated to compare the line widths of the complexes. The largest mode (45 km s-1) of the FWHM distributions among the complexes is in the Clump 2. The value of the mode tends to be smaller at the farther complexes from the GC.

• Chang-Won Lee(Korea Astronomy Observatory)
• Hyung-Mok Lee(SEES, Seoul National University)