Spatial Distribution of HOCN Around Sagittarius B2

Abstract HOCN and HNCO abundance ratio in molecular gas can tell us the information of their formation mechanism. We performed high-sensitivity mapping observations HOCN, HNCO, HNC 18 O lines around Sagittarius B2 (Sgr B2) with IRAM 30 m telescope at 3 mm wavelength. 4 04 –3 03 are used to obtain HOCN. The is calculate optical depth . observed range from 0.4% 0.7% toward most positions, which agrees well gas-grain model. However, relative be enhanced direction Sgr (S), ∼0.9%. reason for that still needs further investigation. Based on intensity lines, we updated isotopic 16 O/ 296 ± 54 B2.