Multiphoton Ionization Photoelectron Spectroscopy of Iodine-Bearing Molecules.

Multiphoton ionization of iodine-bearing molecules has been studied, under collision-free conditions, by observing the kinetic energy of the ejected photoelectrons. These experiments have demonstrated that, for photoionization of I_2, CF_3I and HI at 532 nm, the scission of the R-I bond (R=I, CF _3, HI) is favored over direct ionization of the molecule at intensities in the range of 10 ^{12}-10^{13 }W/cm^2. For the parent molecules studied, we have observed that the atomic iodine photofragment is predominantly formed in the ^2 P_{3/2} and ^2P_{1/2}^in-orbit terms of the atomic iodine ground state. Subsequent 5-photon ionization at 532 nm from the ^2 P_{3/2} and ^2P_{1/2} ground states of the fragment preferably produces ions in the ^3P_2 and ^3P_1<=vels of the ion ground state. These results are consistent with production of the atomic iodine fragment prior to ionization of the parent molecule. Above-threshold ionization is observed for atomic iodine excited from both the ^2P_{3/2} and ^2P_{1/2 } ground states. Only weak evidence was found for molecular ionization of I_2 at the extremes of intensities studied. For HI, however, the production of the v ^' = 0,1 levels of the ^2Pi_{1/2} state of the ion and the v^' = 0,1,2,3,4 levels of the ^2Pi_ {3/2} state of the molecule is reported.