2022MNRAS.512.4419P

Investigating the physical and chemical structure of massive star-forming regions is critical for understanding the formation and early evolution of massive stars. We performed a detailed line survey toward six dense cores, named MM1, MM4, MM6, MM7, MM8, and MM11, in the G9.62+0.19 star-forming region resolved in Atacama Large Millimeter/submillimeter Array (ALMA) band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species, including organic oxygen-, nitrogen-, and sulphur-bearing molecules and their isotopologues. Four dense cores, MM7, MM8, MM4, and MM11, are line-rich sources. Modelling of these spectral lines reveals that the rotational temperature lies in the range 72-115, 100-163, 102-204, and 84-123 K for MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 x 10¹⁵-9.2 x 10¹⁷ cm^–2 toward the four cores. The cores MM8 and MM4 show a chemical difference between oxygen- and nitrogen-bearing species, i.e. MM4 is rich in oxygen-bearing molecules, while nitrogen-bearing molecules, especially vibrationally excited HC₃N lines, are mainly observed in MM8. The distinct initial temperatures at the accretion phase may lead to this N/O differentiation. Through analysing column densities and spatial distributions of O-bearing complex organic molecules (COMs), we found that C₂H₅OH and CH₃OCH₃ might have a common precursor, CH₃OH. CH₃OCHO and CH₃OCH₃ are likely chemically linked. In addition, the observed variation in HC₃N and HC₅N emission may indicate their different formation mechanisms in hot and cold regions.