Relativistic many-body calculations of multipole (E1, M1, E2, M2) transition properties in Al II

We present systematic relativistic many-body calculations of multipole transition properties for singly charged aluminum ion (Al II) using a method that combines configuration interaction and many-body perturbation theory (CI + MBPT). Our calculations cover the 103 lowest energy levels in Al II. For five key low-lying states (3s^{2 1}S₀, 3s3p ³P₀, 3s3p ³P₁, 3s3p ³P₂, and 3s3p ¹P₁), we tabulate the transition wavelengths, reduced matrix elements, transition probabilities, and oscillator strengths for about 400 electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions arising from these levels. Our calculated values agree well with available experimental data and other high-precision theoretical calculations, with typical deviations on the order of 1%. Notably, we report over 80% of these transition lines as previously unreported, significantly expanding the existing spectroscopic database for Al II. These results can serve as a valuable reference resource for ongoing precision quantum metrology as well as astrophysical spectroscopy involving the Al II ion.