The nuclear quadrupole moment of 73Ge from molecular microwave data

Abstract

Large basis set calculations of the electric field gradient at the Ge nucleus have been carried out for GeO and GeS with the purpose to determine the ‘molecular’ value of the quadrupole moment of the 73Ge nucleus from the known quadrupole coupling constants. The electron correlation contribution to the electric field gradient has been determined at the level of the coupled cluster approximation with iterative determination of the effect of single and double substitutions followed by the perturbative estimate of the effect of triple excitations (CCSD(T)). Also the relativistic effects have been taken into account within the framework of the Douglas—Kroll approximation. The vibrationally corrected Douglas—Kroll CCSD(T) results for electric field gradients at Ge in GeO and GeS led to the ‘molecular’ value of the quadrupole moment of the 73Ge nucleus equal to −0.196 b with the estimated error bars in the range of at most a few per cent. This result improves upon the currently used, highly inaccurate ‘atomic’ value (−0.173 ± 0.026 b) of the nuclear quadrupole moment of 73Ge and is suggested as a new recommended value to be used in nuclear physics.