X ray absorption spectroscopy of FeH to aid its identification in astrochemical environments

We present the first absorption spectrum of the unperturbed diatomic molecular ion FeH in any wavelength range. The cryogenic X ray absorption spectrum at the L2 and L3 edge is consistent with an iron 3d occupation of 6.24e. Comparison with the interstellar absorption spectrum of Cygnus X 1 indicates that FeH cannot be ruled out as a component of the absorbing mediu

Zero-Point-Energy Driven Isotopic Exchange of the [H₃O]<SUP>-</SUP> anion Probed by Mid-Infrared Action Spectroscopy

We present the first observation of vibrational transitions in the [H3O](-) anion, an intermediate in the anion-molecule reaction of water, H2O, and hydride, H-, using a laser-induced isotopic H/D exchange reaction action spectroscopy scheme applied to anions. The observed bands are assigned as the fundamental and first overtone of the H2O-H- vibrational stretching mode, based on anharmonic calculations within the vibrational perturbation theory and vibrational configuration interaction. Although the D2OD- species has the lowest energy, our experiments confirm the D2OH- isotope to be a sink of the H/D exchange reaction. Ab initio calculations corroborate that the formation of D2OH- is favored, as the zero-point-energy difference is larger between D-2 and H-2 than between D2OH- and D2OD-

IR multiple photon dissociation spectroscopy of MO2 (+) (M = V, Nb, Ta)

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Size resolved infrared spectroscopy of Na(CH3OH)(n) (n=4-7) clusters in the OH stretching region: unravelling the interaction of methanol clusters with a sodium atom and the emergence of the solvated electron

Size resolved IR action spectra of neutral sodium doped methanol clusters have been measured using IR excitation modulated photoionisation mass spectroscopy. The Na(CH3OH)(n) clusters were generated in a supersonic He seeded expansion of methanol by subsequent Na doping in a pick-up cell. A combined analysis of IR action spectra, IP evolutions and harmonic predictions of IR spectra (using density functional theory) of the most stable structures revealed that for n = 4, 5 structures with an exterior Na atom showing high ionisation potentials (IPs) of similar to 4 eV dominate, while for n = 6, 7 clusters with lower IPs (similar to 3.2 eV) featuring fully solvated Na atoms and solvated electrons emerge and dominate the IR action spectra. For n = 4 simulations of photoionisation spectra using an ab initio MD approach confirm the dominance of exterior structures and explain the previously reported appearance IP of 3.48 eV by small fractions of clusters with partly solvated Na atoms. Only for this cluster size a shift in the isomer composition with cluster temperature has been observed, which may be related to kinetic stabilisation of less Na solvated clusters at low temperatures. Features of slow fragmentation dynamics of cationic Na+(CH3OH)(6) clusters have been observed for the photoionisation near the adiabatic limit. This finding points to the relevance of previously proposed non-vertical photoionisation dynamics of this system

Communications: Observation of two classes of isomers of hydrated electrons in sodium-water clusters

A new class of sodium-water clusters with a low lying ionization potential (IP) is characterized by their photoionization spectra in molecular beam experiments. This implies that Na(H(2)O)(n) clusters coexist for n >= 15 in two forms of significant abundances being distinguished by their IPs of similar to 2.8 and similar to 3.2 eV. A tentative quantum chemical characterization was achieved by simulating ionization spectra for selected cluster sizes using an ab initio molecular dynamics approach. Experiment and theory suggest that the Na(+)-e(-) distance is significantly larger in the clusters with the lower IP. This indicates that the solvated electron in Na(H(2)O)(n) clusters very probably forms with the Na(+) counterion both a solvent separated and a contact ion pair. (C) 2010 American Institute of Physics. [doi:10.1063/1.3439393]DFG [ZE 890-1-1]; Czech Republic [P208/10/1724

On the nature and origin of dicationic, charge-separated species formed in liquid water on X-ray irradiation

To understand the yield and patterns of damage in aqueous condensed matter, including biological systems, it is essential to identify the initial products subsequent to the interaction of high energy radiation with liquid water. Until now, the observation of several fast reactions induced by energetic particles in water was not possible on their characteristic timescales. Therefore, some of the reaction intermediates involved, particularly those that require nuclear motion, were not considered when describing radiation chemistry. Here, through a combined experimental and theoretical study, we elucidate the ultrafast proton dynamics in the first few femtoseconds after X ray core level ionization of liquid water. We show through isotope analysis of the Auger spectra that proton transfer dynamics occur on the same timescale as electron autoionization. Proton transfer leads to the formation of a Zundel type intermediate [HO H H2O] , which further ionizes to form a so far unnoticed type of dicationic charge separated species with high internal energy. We call the process proton transfer mediated charge separatio

Considerable matrix shift in the electronic transitions of helium-solvated cesium dimer cation Cs2Hen+

We investigate the photodissociation of helium-solvated cesium dimer cations using action spectroscopy and quantum chemical calculations. The spectrum of Cs2He+ shows three distinct absorption bands into both bound and dissociative states. Upon solvation with further helium atoms, considerable shifts of the absorption bands are observed, exceeding 0.1 eV (850 cm-1) already for Cs2He10+, along with significant broadening. The shifts are highly sensitive to the character of the excited state. Our calculations show that helium atoms adsorb on the ends of Cs2+. The shifts are particularly pronounced if the excited state orbitals extend to the area occupied by the helium atoms. In this case, Pauli repulsion leads to a deformation of the excited state orbitals, resulting in the observed blue shift of the transition. Since the position of the weakly bound helium atoms is ill defined, Pauli repulsion also explains the broadening.(VLID)4795191Version of recor

Transforming Anion Instability into Stability Contrasting Photoionization of Three Protonation Forms of the Phosphate Ion upon Moving into Water

We use photoelectron emission spectroscopy with vacuum microjet technique and quantum chemistry calculations to investigate electronic structure and stability of aqueous phosphate anions. On the basis of the measured photoelectron spectra of sodium phosphates at different pH, we report the lowest vertical ionization energies of monobasic 9.5 eV , dibasic 8.9 eV , and tribasic 8.4 eV anions. Electron binding energies were in tandem modeled with ab initio methods, using a mixed dielectric solvation model together with up to 64 explicitly solvating water molecules. We demonstrate that two solvation layers of explicit water molecules are needed to obtain converged values of vertical ionization energies VIEs within this mixed solvation model, leading to very good agreement with experiment. We also show that the highly charged PO43 anion, which is electronically unstable in the gas phase, gains the electronic stability with about 16 water molecules, while only 2 3 water molecules are sufficient to stabilize the doubly charged phosphate anion. We also investigate the effect of ion pairing on the vertical ionization energy. In contrast to protonation leading to a formation of covalent O H bond , sodiation leading to an anion Na ion pair has only a weak effect on the electron binding energ