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

The nuclear quadrupole moment, Q, of Al-27 has been determined by combining molecular measurements on AlF and AlCl with electric field gradients calcu lated at CCSD(T) level as well as by combining atomic measurements on Al(3p P-3(3/2)) with the electric field gradient obtained at numerical MCHF leve l. The 'molecular' Q(Al) values obtained are 146.2-147.2 millibarn (1 mb = 10(-31) m(2)) while the 'atomic' one is 146.6 mb. Due to inclusion of highe r-order core excitations, the 'atomic' Q! value is increased by 4% as compa red to the previous atomic MCHF determination. The recommended value for Q( Al-27) is 146.6(1.0) mb. (C) 1999 Elsevier Science B.V. All rights reserved .