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A semiquantitative study of the intermolecular Coulombic decay (ICD) of singly and doubly ionized water dimer has been carried out with the help of ab initio computed ionization spectra and potential energy curves (PECs). These PECs are particular cuts through the (H2O)2, (H2O)2+, and (H2O)2++ hypersurfaces along the distance between the two oxygen atoms. A comparison with the recently published experimental data for the ICD in singly ionized water dimers [T. Jahnke, H. Sann, T. Havermeier et al., Nat. Phys. 6, 139 (2010)] and in large water clusters [M. Mucke, M. Braune, S. Barth et al., Nat. Phys. 6, 143 (2010)] shows that such a simplified description in which the internal degrees of freedom of the water molecules are frozen gives surprisingly useful results. Other possible decay channels of the singly ionized water dimer are also investigated and the influence of the H-atom participating in the hydrogen bond on the spectra of the proton-donor and proton-acceptor molecules in the dimer is discussed. Importantly, the decay processes of one-site dicationic states of water dimer are discussed and an estimate of the ICD-electron spectra is made. More than 33% of the dications produced by Auger decay are found to undergo ICD. The qualitative results show that the ICD following Auger decay in water is also expected to be an additional source of low-energy electrons proven to be extremely important for causing damages to living tissues. [ABSTRACT FROM AUTHOR]

Low-lying relaxation satellites give rise to ultrafast electron dynamics following outer-valence ionization of a molecular system. To demonstrate the impact of such satellites, the evolution of the electronic cloud after sudden removal of an electron from the highest occupied molecular orbital (HOMO) of the organic unsaturated nitroso compound 2-nitroso[1,3]oxazolo[5,4-d][1,3]oxazole is traced in real time and space using ab initio methods only. Our results show that the initially created hole charge remains stationary but on top of it the system reacts by an ultrafast π-π* excitation followed by a cyclic excitation-de-excitation process which leads to a redistribution of the charge. The π-π* excitation following the removal of the HOMO electron takes place on a subfemtosecond time scale and the period of the excitation-de-excitation alternations is about 1.4 fs. In real space the processes of excitation and de-excitation represent ultrafast delocalization and localization of the charge. The results are analyzed by simple two- and three-state models. [ABSTRACT FROM AUTHOR]

Abstract: Due to many-body effects an ultrafast removal of an electron from a molecule can trigger electron dynamics in which the created hole charge migrates throughout the system on a few-femtoseconds time scale. Here we report ab initio calculations of the positive-charge migration following inner-valence ionization of the C-terminally methylamidated dipeptide Gly–Gly–NH–CH3. To investigate the influence of the molecular symmetry on the process, two different conformations of the system are studied. Our results show that in both conformers the charge initially localized on the methylamine end of the system migrates to the remote glycine in only 5–6fs jumping thereby over an entire amino acid. Our computations also show that the symmetry of the system facilitates the process – a larger fraction of the charge migrates over a larger distance if the molecule is symmetric. Ionization spectra of both studied conformers are also reported. [Copyright &y& Elsevier]

Abstract: Based on elaborated ab initio calculations we first study the ionization spectra of the free-base porphyrin (H2-P) and Mg(II) porphyrin (Mg-P). Then we investigate the ultrafast electron dynamics following outer-valence ionization of these systems which constitutes the highlight of this paper. It is shown that the electron correlation effects are very strong in these systems giving rise to pronounced shake-down satellites in the outer-valence part of the ionization spectra. We show that due to these strong correlation effects the removal of an electron from the 3b 1g orbital of H2-P and Mg-P leads to an ultrafast reorganization of the electronic cloud. After being initially localized on the B and D pyrrole rings, the hole charge created upon ionization spreads throughout the molecule in only few femtoseconds. In both systems the electron dynamics triggered by the ionization represent alternating ultrafast delocalizations and localizations of the charge. The results may also give a hint on the nuclear dynamics in the free-base and Mg(II) porphyrin radical cations that will follow the ultrafast charge migration. [Copyright &y& Elsevier]

Abstract: The migration of hole charge created via ionization of the main conformers of the gaseous amino acid glycine is studied. The migration is ultrafast and is mediated solely by many-electron effects, i.e. electronic correlation and relaxation. The influence of the nuclear geometry is investigated by studying the three most abundant conformers of glycine. It is shown that the electron dynamics following ionization can be dramatically different for the different conformers. To facilitate the discussion of the charge migration, the ionization spectra of the conformers are computed as well. [Copyright &y& Elsevier]

After the ionization of a valence electron, the created hole can migrate ultrafast from one end of the molecule to another. Because of the advent of attosecond pulse techniques, the measuring and understanding of charge migration has become a central topic in attosecond science. Here, we pose the hitherto unconsidered question whether ionizing a core electron will also lead to charge migration. It is found that the created hole in the core stays put, but in response to this hole interesting electron dynamics takes place which can lead to intense charge migration in the valence shell. This migration is typically faster than that after the ionization of a valence electron and transpires on a shorter time scale than the natural decay of the core hole by the Auger process, making the subject very challenging to attosecond science. [ABSTRACT FROM AUTHOR]

To exploit the high intensity of laser radiation, we propose to select frequencies at which single-photon absorption is of too low energy and two or more photons are needed to produce states of an atom that can undergo interatomic Coulombic decay (ICD) with its neighbors. For Ne2 it is explicitly demonstrated that the proposed multiphoton absorption scheme is much more efficient than schemes used until now, which rely on single-photon absorption. Extensive calculations on Ne2 show how the low-energy ICD electrons and Ne+ pairs are produced for different laser intensities and pulse durations. At higher intensities the production of Ne+ pairs by successive ionization of the two atoms becomes competitive and the respective emitted electrons interfere with the ICD electrons. It is also shown that a measurement after a time delay can be used to determine the contribution of ICD even at high laser intensity. [ABSTRACT FROM AUTHOR]

Ionization of molecules very often populates several cationic states launching pure electron dynamics that appear as ultrafast migration of the hole charge throughout the system. A crucial question in the emerging field of attochemistry is whether these pure electronic coherences last long enough to allow for their efficient observation and eventual manipulation with ultrashort laser pulses. We report a full-dimensional quantum calculation of concerted electron-nuclear dynamics initiated by outer-valence ionization of propiolic acid molecule, showing that the charge will oscillate between the carbon triple bond and the carbonyl oxygen for more than 10 fs before getting trapped by the nuclear motion. This time is enough for the charge migration to be observed and controlled. We argue that the molecule is very suitable for experimental studies. [ABSTRACT FROM AUTHOR]