Experimental infrared spectra and theoretical harmonic and anharmonic IR spectra of pyrene (C₁₆H₁₂) in neutral and cationic states. The dotted lines indicate the characteristic positions of the interstellar AIBs. The experimental spectra are based on matrix-isolated PAHdb data and are reconstructed from transition intensities (A-values) using a Gaussian line profile with a uniform FWHM (=12 cm⁻¹), ensuring consistent broadening across all spectra.