Multiphoton Dissociative Ionization of Gas-Phase Styrene.

We performed multiphoton ionization of styrene molecules and observed the formation of styrene and benzene cations, the latter being reported for the first time in the multiphoton ionization of styrene. The formation of the benzene cation reveals an internal conversion from the S state to the S state, which occurs via a S/S conical intersection at 4.66 eV above the minimum of the S state.

Molecular growth of PANH via intermolecular Coulombic decay.

Nitrogen-bearing polycyclic aromatic hydrocarbons (PANHs) are ubiquitous in space. They are considered precursors to advanced biomolecules identified in meteorites. However, their chemical evolution into biomolecules in photodestructive astrophysical mediums remains a paradox.

Ambient-light-induced intermolecular Coulombic decay in unbound pyridine monomers.

Intermolecular Coulombic decay (ICD) is a process whereby photoexcited molecules relax by ionizing their neighbouring molecules. ICD is efficient when intermolecular interactions are active and consequently it is observed only in weakly bound systems, such as clusters and hydrogen-bonded systems. Here we report an efficient ICD between unbound molecules excited at ambient-light intensities.

Strong-field ionization of CHCl: proton migration and association.

Strong-field ionization of CHCl using femtosecond laser pulses, and the subsequent two-body dissociation of CHCl along H ( = 1-3) and HCl forming pathways, have been experimentally studied in a home-built COLTRIMS (cold target recoil ion momentum spectrometer) setup. The single ionization rate of CHCl was obtained experimentally by varying the laser intensity from 1.6 × 10 W cm to 2.

Strong-field ionization of polyatomic molecules: ultrafast H atom migration and bond formation in the photodissociation of CHOH.

Strong-field ionization induces various complex phenomena like bond breaking, intramolecular hydrogen migration, and bond association in polyatomic molecules. The H-atom migration and bond formation in CH3OH induced by intense femtosecond laser pulses are investigated using a Velocity Map Imaging (VMI) spectrometer. Various laser parameters like intensity (1.

Multi-slit-type interference in carbon 2s photoionization of polyatomic molecules: from a fundamental effect to structural parameters.

In molecular photoemission, the analogue of the celebrated Young's double slit experiment is coherent electron emission from two equivalent atomic centers, giving rise to an interference pattern. Here multi-slit interference is investigated in inner-valence photoionization of propane, n-butane, isobutane and methyl peroxide. A more complex pattern is observed due to molecular orbital delocalization in polyatomic molecules, blurring the distinction between interference and diffraction.

Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect.

Observing and controlling molecular motion and in particular rotation are fundamental topics in physics and chemistry. To initiate ultrafast rotation, one needs a way to transfer a large angular momentum to the molecule. As a showcase, this was performed by hard X-ray C1s ionization of carbon monoxide accompanied by spinning up the molecule via the recoil "kick" of the emitted fast photoelectron.

Quantitative estimation of elemental composition employing a synthetic generated spectrum.

Composition of multielement samples is estimated by using a synthetic generated spectrum utilizing a nonlinear fitting routine. By fitting simultaneously a large number of emission lines, the error in the estimation is minimized. The procedure for synthetic spectrum generation includes self-absorption of emission lines by taking into account the number density of different species in the plasma.

Isomer-dependent fragmentation dynamics of inner-shell photoionized difluoroiodobenzene.

The fragmentation dynamics of 2,6- and 3,5-difluoroiodobenzene after iodine 4d inner-shell photoionization with soft X-rays are studied using coincident electron and ion momentum imaging. By analyzing the momentum correlation between iodine and fluorine cations in three-fold ion coincidence events, we can distinguish the two isomers experimentally. Classical Coulomb explosion simulations are in overall agreement with the experimentally determined fragment ion kinetic energies and momentum correlations and point toward different fragmentation mechanisms and time scales.

Strong-field-induced wave packet dynamics in carbon dioxide molecule.

Temporal evolution of electronic and nuclear wave packets created in strong-field excitation of the carbon dioxide molecule is studied employing momentum-resolved ion spectroscopy and channel-selective Fourier analysis. Combining the data obtained with two different pump-probe set-ups, we observed signatures of vibrational dynamics in both, ionic and neutral states of the molecule. We consider far-off-resonance two-photon Raman scattering to be the most likely mechanism of vibrational excitation in the electronic ground state of the neutral CO.

Electronic state-lifetime interference in resonant Auger spectra: a tool to disentangle overlapping core-excited states.

We have measured resonant-Auger decay following Cl 1s(-1) excitations in HCl and CH3Cl molecules, and extracted the pseudo-cross sections of different Cl 2p(-2) final states. These cross sections show clear evidence of shake processes as well as contributions of electronic state-lifetime interference (ELI). To describe the spectra we developed a fit approach that takes into account ELI contributions and ultrafast nuclear dynamics in dissociative core-excited states.

Direct observation of double-core-hole shake-up States in photoemission.

Direct measurements of Ar^{+} 1s^{-1}2p^{-1}nl double-core-hole shake-up states are reported using conventional single-channel photoemission, offering a new and relatively easy means to study such species. The high-quality results yield accurate energies and lifetimes of the double-core-hole states. Their photoemission spectrum also can be likened to 1s absorption of an exotic argon ion with a 2p core vacancy, providing new information about the spectroscopy of both this unusual ionic state as well as the neutral atom.

Atomic Auger Doppler effects upon emission of fast photoelectrons.

Studies of photoemission processes induced by hard X-rays including production of energetic electrons have become feasible due to recent substantial improvement of instrumentation. Novel dynamical phenomena have become possible to investigate in this new regime. Here we show a significant change in Auger emission following 1s photoionization of neon, which we attribute to the recoil of the Ne ion induced by the emission of a fast photoelectron.

From double-slit interference to structural information in simple hydrocarbons.

Interferences in coherent emission of photoelectrons from two equivalent atomic centers in a molecule are the microscopic analogies of the celebrated Young's double-slit experiment. By considering inner-valence shell ionization in the series of simple hydrocarbons C2H2, C2H4, and C2H6, we show that double-slit interference is widespread and has built-in quantitative information on geometry, orbital composition, and many-body effects. A theoretical and experimental study is presented over the photon energy range of 70-700 eV.