Time-Resolved Probing of the Iodobenzene C-Band Using XUV-Induced Electron Transfer Dynamics.

Time-resolved extreme ultraviolet spectroscopy was used to investigate photodissociation within the iodobenzene C-band. The carbon-iodine bond of iodobenzene was photolyzed at 200 nm, and the ensuing dynamics were probed at 10.3 nm (120 eV) over a 4 ps range.

The Role of Momentum Partitioning in Covariance Ion Imaging Analysis.

We present results from a covariance ion imaging study, which employs extensive filtering, on the relationship between fragment momenta to gain deeper insight into photofragmentation dynamics. A new data analysis approach is introduced that considers the momentum partitioning between the fragments of the breakup of a molecular polycation to disentangle concurrent fragmentation channels, which yield the same ion species. We exploit this approach to examine the momentum exchange relationship between the products, which provides direct insight into the dynamics of molecular fragmentation.

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes site-selective ionization.

C-I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy.

Disentangling sequential and concerted fragmentations of molecular polycations with covariant native frame analysis.

We present results from an experimental ion imaging study into the fragmentation dynamics of 1-iodopropane and 2-iodopropane following interaction with extreme ultraviolet intense femtosecond laser pulses with a photon energy of 95 eV. Using covariance imaging analysis, a range of observed fragmentation pathways of the resulting polycations can be isolated and interrogated in detail at relatively high ion count rates (∼12 ions shot). By incorporating the recently developed native frames analysis approach into the three-dimensional covariance imaging procedure, contributions from three-body concerted and sequential fragmentation mechanisms can be isolated.

Multi-channel photodissociation and XUV-induced charge transfer dynamics in strong-field-ionized methyl iodide studied with time-resolved recoil-frame covariance imaging.

The photodissociation dynamics of strong-field ionized methyl iodide (CH3I) were probed using intense extreme ultraviolet (XUV) radiation produced by the SPring-8 Angstrom Compact free electron LAser (SACLA). Strong-field ionization and subsequent fragmentation of CH3I was initiated by an intense femtosecond infrared (IR) pulse. The ensuing fragmentation and charge transfer processes following multiple ionization by the XUV pulse at a range of pump-probe delays were followed in a multi-mass ion velocity-map imaging (VMI) experiment.

Probing molecular bond-length using molecular-frame photoelectron angular distributions.

The molecular-frame photoelectron angular distributions (MFPADs) in O 1s photoemission from CO molecule were measured. Patterns due to photoelectron diffractions were observed in the MFPADs. The polarization-averaged MFPADs were compared with theoretical calculation and were found to be useful in determining the molecular bond-length, which is a component to determine molecular structures.

Superfluorescence, Free-Induction Decay, and Four-Wave Mixing: Propagation of Free-Electron Laser Pulses through a Dense Sample of Helium Ions.

We report an experimental and numerical study of the propagation of free-electron laser pulses (wavelength 24.3 nm) through helium gas. Ionization and excitation populates the He^{+} 4p state.

Demonstration of up-conversion fluorescence from Ar clusters in intense free-electron-laser fields.

Extreme ultraviolet (EUV) fluorescence emitted from Ar clusters irradiated by intense EUV free electron laser (FEL) pulses has been investigated. The EUV fluorescence spectra display rich structure at wavelengths shorter than the incident FEL wavelength of 51 nm. The results suggest that multiply-charged ions are produced following the ion-electron recombination processes which occur in the nanoplasma created by multi-photon excitation during the intense EUV-FEL pulses.

Observation of free-electron-laser-induced collective spontaneous emission (superfluorescence).

We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 1s(2) → 1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation.

Recoil excitation of vibrational structure in the carbon 1s photoelectron spectrum of CF4.

The carbon 1s photoelectron spectrum of CF4 measured at photon energies from 330 to 1500 eV shows significant contributions from nonsymmetric vibrational modes. These increase linearly as the photon energy increases. The excitation of these modes, which is not predicted in the usual Franck-Condon point of view, arises from the recoil momentum imparted to the carbon atom in the ionization process.

Boron 1s photoelectron spectrum of 11BF3: vibrational structure and linewidth.

The boron 1s photoelectron spectrum of (11)BF(3) has been measured at a photon energy of 400 eV and a resolution of about 55 meV. The pronounced vibrational structure seen in the spectrum has been analyzed to give the harmonic and anharmonic vibrational frequencies of the symmetric stretching mode, 128.1 and 0.

Inner-shell excitation spectroscopy and fragmentation of small hydrogen-bonded clusters of formic acid after core excitations at the oxygen K edge.

Inner-shell excitation spectra and fragmentation of small clusters of formic acid have been studied in the oxygen K-edge region by time-of-flight fragment mass spectroscopy. In addition to several fragment cations smaller than the parent molecule, we have identified the production of HCOOH.H+ and H3O+ cations characteristic of proton transfer reactions within the clusters.

Double photoexcitation of helium in a strong dc electric field.

We report the first experimental measurements of the effect of an applied field on the photoexcitation and autoionization of doubly excited states of helium. Ground-state photoionization spectra have been measured in the region below the He+(N=2) threshold with static electric fields of up to 84.4 kV/cm across the interaction region.