Simple cyanides and formylium ions isotopologues in early star-forming molecular cores
Understanding the chemistry related to the early stages of star formation is of great importance, as it is linked to the beginnings of the most complex chemistry in the interstellar medium. In this context, we investigate the chemical behaviour of simple cyano-bearing molecules and formylium ions isotopologues in a sample of massive infrared-quiet molecular cores. Using archive ALMA Band 7 data of 37 early molecular cores embedded in ATLASGAL clumps, we obtain abundances of HC$_{3}$N, H$^{13}$CN, HN$^{13}$C, H$^{13}$CO$^+$, and HC$^{17}$O$^+$. We used various statistical methods, including hierarchical clustering, to analyse the correlations between molecular abundances, ratios and temperature. We find that HN$^{13}$C, H$^{13}$CO$^{+}$, and HC$^{17}$O$^{+}$ abundances correlate positively with kinetic temperature, suggesting temperature-driven chemical regulation in young massive cores. A similar trend is observed for H$^{13}$CN, although the limited number of detections prevents a definitive conclusion. HC$_3$N abundances show no dependence on temperature within the 40-100 K range, suggesting a chemical steady state between gas-phase production and grain-surface depletion. Similarly, the H$^{13}$CN/HN$^{13}$C ratio, measured in only six regions, suggests no correlation with temperature, differing from findings at lower temperatures. Using a hierarchical clustering method based on abundance ratios, novel in astrochemistry, we identified chemically distinct core groups that align with thermal conditions. Additionally, we provide HC$^{17}$O$^+$ detections for 28 cores-a significant expansion of existing literature-and find evidence that H$^{13}$CO$^{+}$ transitions may have higher optical depths than commonly assumed. These results are important because characterizing the chemical state of early star-forming stages is essential for understanding the onset of the most complex chemistry.