Photodissociation dynamics of IrBr62− dianions by time-resolved photoelectron spectroscopy

We have used femtosecond time-resolved photoelectron spectroscopy to examine the photodissociation dynamics of doubly charged anions IrBr62− after excitation at hνpump=1.6 eV and with a detachment photon energy of hνprobe=4.8 eV. Excited state dynamics proceed by successive decay of the initially excited state, by way of an intermediate and back to the electronic ground state. This is associated with lifetimes of τ1=2.1±0.3 ps and τ2=21±2 ps, respectively. After nonadiabatic relaxation, the internal energy of the dianion is sufficiently large to induce fragmentation and delayed emission of Br− over the repulsive Coulomb barrier with a 79±21 ps time constant. As both fragments are negatively charged, Coulomb repulsion at early times (and correspondingly small separations) is reflected in the transient photoelectron spectra. Analysis of both shifts and intensities of the time-dependent bromide detachment features allows determination of the shape of the dissociation barrier. A lower limit of the outer heigh...