2026ApJS..282....7R

Version 4.00 of the library of computed spectra of the NASA Ames PAH IR Spectroscopic Database (PAHdb) includes an expanded set of polycyclic aromatic hydrocarbon (PAH) spectra, totaling 10,749, calculated using the harmonic approximation and a basis set containing polarization functions. The software tools offered through PAHdb have also been significantly expanded, including optimizations to more efficiently handle the large number of spectra now available. Major improvements have been made to the PAHdb website, which now also offers new libraries of laboratory and computed PAH cluster spectra. PAH boundary-edge codes are now being used throughout PAHdb to hold structural information and to search for specific PAH isomers. All enhancements and updates are described in expanded documentation. As a demonstration, the updated version 4.00 computational library and improved software tools are used to analyze the James Webb Space Telescope spectrum of the atomic photodissociation region of the Orion Bar and show a remarkable improvement in matching the 6.2 μm emission band and the 10-15 μm emission over earlier library versions.