Electric quadrupole moment of the 27Al nucleus: Converging results from the AlF and AlCl molecules and the Al atom

The nuclear quadrupole moment, Q, of 27Al has been determined by combining molecular measurements on AlF and AlCl with electric field gradients calculated at CCSD(T) level as well as by combining atomic measurements on Al(3p 2P3/2) with the electric field gradient obtained at numerical MCHF level. The `molecularʹ Q(Al) values obtained are 146.2–147.2 millibarn (1 mb=10−31 m2) while the `atomicʹ one is 146.6 mb. Due to inclusion of higher-order core excitations, the `atomicʹ Q value is increased by 4% as compared to the previous atomic MCHF determination. The recommended value for Q(27Al) is 146.6(1.0) mb.