AN IMPROVED VALUE OF THE NUCLEAR-QUADRUPOLE MOMENT OF THE 197 KEV I=52 EXCITED-STATE OF F-19/

Highly correlated ab initio calculations of the electric field gradien t at the fluorine nuclei in F-2 have been carried out using large and accurate basis sets, yielding results close to the basis ser limit. Co mbination of the experimentally determined quadrupole coupling constan t for F-2 and the calculated electric field gradient has led to a new value of the nuclear quadrupole moment of the I=5/2 excited state at 1 97 keV of the F-19 nucleus, The Q-value obtained is (- 94.2 +/- 0.9) x 10(-31) m(2) (millibarn (mb)), and this value is demonstrated to be s ignificantly more accurate than the old standard value of -72 +/- 4 mb based on self-consistent-field calculations on the FCl molecule. (C) 1997 Elsevier Science B.V.