Photodissociation dynamics of IrBr6(2-) dianions by time-resolved photoelectron spectroscopy

• Published in: The Journal of chemical physics Vol. 130; no. 23; p. 234306
• Main Authors: Rensing, Christian, Ehrler, Oli T, Yang, Ji-Ping, Unterreiner, Andreas-Neil, Kappes, Manfred M
• Format: Journal Article
• Language: English
• Published: United States 21.06.2009
• ISSN: 1089-7690
• DOI: 10.1063/1.3148377

We have used femtosecond time-resolved photoelectron spectroscopy to examine the photodissociation dynamics of doubly charged anions IrBr(6)(2-) after excitation at h nu(pump) = 1.6 eV and with a detachment photon energy of h nu(probe) = 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 tau(1) = 2.1+/-0.3 ps and tau(2) = 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 height was retrieved from the kinetic energy release of KER > or = 1.6 eV. Modeling of the dissociation rate with statistical rate theory results in an inner barrier height of E(RCB) = 0.95 eV.