The planet-forming disk of HD 142527 is known for its azimuthally asymmetric dust trap, shadows, and spiral arms. In this work we used new observations of the Atacama Large Millimeter/submillimeter Array to investigate the molecular composition and to determine the ongoing chemical processes and the origin of its asymmetric molecular emission, and to infer possible effects of dust continuum obscuration. The observations cover a wide variety of molecular species over a large frequency range, enlarging the known molecular inventory of this system. Strikingly, the emission of, , and is dominated by spiral-like features peaking in the southern region of the disk, opposite to the large dust trap, while no relation is found between the observed asymmetries and the shadows seen in the scattered light due to the misaligned inner disk. We attribute these features to low-density, late infalling, atomic carbon-rich material that locally increases the C/O ratio and, subsequently, facilitates the gas-phase formation of these species. Azimuthal offsets between the peak emission of and that of and are possibly due to a delay of a few hundred years in the gas-phase formation of. As opposed to the emission of, , and, the emission of and the J=1-0 transition is aligned with the large dust trap, likely due to an azimuthal increase in the surface density. Differences between the two observed transitions may be due to dust obscuration effects. These effects are not expected to affect molecular emission at 3 mm, given the lower optical depth of the dust trap. The four observed transitions of display different azimuthal extents and strengths, with the lines with lower upper-level energies appearing more ring-like. An analysis of the brightness temperature yields no significant temperature variations across the disk's azimuth. Therefore, we propose that the observed transitions trace two different reservoirs: a cold reservoir that resides on a Keplerian orbit and a second, hotter reservoir of that is facilitated by the infalling material and resides in a higher atmospheric layer of the disk. A single weak transition of is observed, which may be explained by weak shocks induced by the spirals observed in the scattered light that liberate sulphur. Future higher-resolution, multi-line observations of species such as, , , and are needed to investigate the role and importance of late infalling material in setting the chemical composition of planet-forming disks. H₂CO CN C₂H H₂CO CN C₂H H₂CO H₂CO CN C₂H C^ 17 O HCO^+ C^ 17 O CS ^ 13 CO CS CS SO H₂CO CS CN C₂H
Temmink et al. (Tue,) studied this question.