A Comprehensive Multi-Molecular Investigation of the HD 163296 Chemistry: From Observed Organics and Nitriles to Sulfates and Deuterated Species Using ALMA

The physical and chemical conditions within a protoplanetary disk play a crucial role in determining its chemical content, which is subsequently inherited by the forming planets. To probe these conditions, high-resolution molecular line observations coupled with accurate models are essential. In this study, we investigated the molecular chemistry of the nearby, massive, and relatively line-rich protoplanetary disk HD 163296 using high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations across Bands 3, 4, 6, and 7. We constrained the disk-averaged and radial distribution of column density and excitation temperature for the detected molecules using our in-house retrieval code DRive. We modelled the chemistry of the disk using our in-house chemical model PEGASIS while varying initial elemental C/O ratios and cosmic ray ionisation rates. Notably, this study is the first to incorporate an extensive deuterated species network based on KIDA 2024. Our results provide the first and most stringent upper limits on the column densities of NH2CHO and HNCO in any protoplanetary disk, measuring 6.73 x 10^11 cm^-2 and 1.29 x 10^11 cm^-2, respectively. We also present the highest-resolution DCO+ emission map in the disk, revealing triple-ringed chemical substructures that closely correspond to the continuum substructures. This work establishes a strong constraint on the C/O ratio at 1.1. Our chemical models suggest that NH2CHO and HNCO primarily form on grain surfaces within the protoplanetary disk environment, with desorption processes proving insufficiently efficient to produce detectable gas-phase abundances given current ALMA capabilities.