ABSOLUTE INTEGRATED BAND STRENGTH AND MAGNETIC DIPOLE TRANSITION MOMENTS IN THE P-2(3 2)-]P-2(1/2) FINE-STRUCTURE (WITH HYPERFINE-STRUCTURE) TRANSITION OF THE IODINE ATOM - EXPERIMENT AND THEORY/

Previous experimental and theoretical results on the strength of the i mportant fine structure transition in the Iodine atom scatter over a v ery wide range, indicating great uncertainty. We have therefore carrie d out new theoretical calculations and experiments to reinvestigate th e transition probability between the fine structure levels P-2(3/2) an d P-2(1/2) the electronic ground configuration of atomic iodine. In th e experiments a tunable, narrow band width, near-IR laser was used to measure the iodine absorption spectrum with sub-Doppler resolution. Th e I-atoms in the P-2(3/2) ground stale are produced either in a I-2 = 2I equilibriums at elevated temperatures or from IR-multiphoton dissoc iation of CF3I, CF3CHFI or C6F5I. The two different experimental metho ds to produce I-atoms in the ground state allow for a careful check on possible systematic errors. In the experiments an integrated absorpti on cross section of G(exp) = integral sigma(nu)dln nu = (1050+/-250) f m(2) was determined, corresponding to a radiative lifetime of 140 ms f or spontaneous emission from the upper level. We have in addition carr ied out nonrelativistic MCHF calculations and relativistic Dirac-Fock calculations on this transition. The results of the MCHF calculations (1200 fm(2)) agree well with experiment and a crude estimate from a si mple LS coupling model.