Absolute Integrated Band Strength and Magnetic Dipole Transition Moments in the 2 P 3/2 → 2 P 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 important fine structure transition in the Iodine atom scatter over a very wide range, indicating great uncertainty. We have therefore carried out new theoretical calculations and experiments to reinvestigate the transition probability between the fine structure levels 2 P 3/2 and 2 P 1/2 in the electronic ground configuration of atomic iodine. In the experiments a tunable, narrow band width, near‐IR laser was used to measure the iodine absorption spectrum with sub‐Doppler resolution. The I‐atoms in the 2 P 3/2 ground state are produced either in a I 2 = 2I equilibriums at elevated temperatures or from IR‐multiphoton dissociation of CF 3 I, CF 3 CHFI or C 6 F 5 I. The two different experimental methods to produce I‐atoms in the ground state allow for a careful check on possible systematic errors. In the experiments an integrated absorption cross section of G exp = ∫ σ( v ) dln v = (1050±250) fm 2 was determined, corresponding to a radiative lifetime of 140 ms for spontaneous emission from the upper level. We have in addition carried 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 simple LS coupling model.