2022RAA....22c5007Z

HOCN and HNCO abundance ratio in molecular gas can tell us the information of their formation mechanism. We performed high-sensitivity mapping observations of HOCN, HNCO, and HNC¹⁸O lines around Sagittarius B2 (Sgr B2) with the IRAM 30 m telescope at the 3 mm wavelength. HNCO 4₀₄-3₀₃ and HOCN 4₀₄-3₀₃ are used to obtain the abundance ratio of HNCO to HOCN. The ratio of HNCO 4₀₄-3₀₃ to HNC¹⁸O 4₀₄-3₀₃ is used to calculate the optical depth of HNCO 4₀₄-3₀₃. The abundance ratio of HOCN and HNCO is observed to range from 0.4% to 0.7% toward most positions, which agrees well with the gas-grain model. However, the relative abundance of HOCN is observed to be enhanced toward the direction of Sgr B2 (S), with HOCN to HNCO abundance ratio of ∼0.9%. The reason for that still needs further investigation. Based on the intensity ratio of HNCO and HNC¹⁸O lines, we updated the isotopic ratio of ¹⁶O/¹⁸O to be 296 ± 54 in Sgr B2.