Core-to-Rydberg band shift and broadening of hydrogen bonded ammonia clusters studied with nitrogen K-edge excitation spectroscopy

Nitrogen 1s (N 1s) core-to-Rydberg excitation spectra of hydrogen-bonded clusters of ammonia (AM) have been studied in the small cluster regime of beam conditions with time-of-flight (TOF) fragmentmass spectroscopy. By monitoring partial-ion-yield spectra of cluster-origin products, "cluster" specific excitation spectra could be recorded. Comparison of the "cluster" band with "monomer" band revealed that the first resonance bands of clusters corresponding to N 1s -> 3sa(1)/3pe of AM monomer are considerably broadened. The changes of the experimental core-to-Rydberg transitions Delta FWHM (N 1s -> 3sa(1)/3pe) = similar to 0.20/similar to 0.50 eV compare well with the x ray absorption spectra of the clusters generated by using density functional theory (DFT) calculation. The broadening of the core-to-Rydberg bands in small clusters is interpreted as being primarily due to the splitting of non-equivalent core-hole N 1s states caused by both electrostatic core-hole and hydrogen-bonding (H(3)N center dot center dot center dot H-NH(2)) interactions upon dimerization. Under Cs dimer configuration, core-electron binding energy of H-N (H-donor) is significantly decreased by the intermolecular core-hole interaction and causes notable redshifts of core-excitation energies, whereas that of lone-pair nitrogen (H-acceptor) is slightly increased and results in appreciable blueshifts in the core-excitation bands. The result of the hydrogen-bonding interaction strongly appears in the n-sigma* orbital correlation, destabilizing H-N donor Rydberg states in the direction opposite to the core-hole interaction, when excited N atom with H-N donor configuration strongly possesses the Rydberg component of anti-bonding sigma* (N-H) character. Contributions of other cyclic H-bonded clusters (AM)(n) with n >= 3 to the spectral changes of the N 1s -> 3sa(1)/3pe bands are also examined. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3673778

Shake-off of loosely bound electrons in Auger decays of Kr 2p core hole states

Multicharged Kr ions have been measured using monochromatized undulator radiation combined with a coincidence technique. It has been found that a charge-state distribution of Kr ions being coincident with satellite peaks of Kr 2p3/2 photoelectron is slightly different from that for the main line. Resonant Auger peaks for 2p–1nl-->1G4 nl transitions generated essentially Kr4+ only, which differs from the charge-state distribution for the normal Auger peak. These findings suggest that loosely bound electrons in high Rydberg orbitals are easily shaken-off in electron emission processes.Erratum is added on the last page

Anisotropic velocity distribution of desorbing product in carbon monoxide oxidation on palladium (110)

Significant anisotropy was found in the velocity distributions of desorbing product CO2 from a Pd(110) surface. The velocity distributions were determined by a cross-correlation time-of-flight technique combined with angle-resolved thermal desorption. Heating the coadlayer of CO and oxygen produces five peaks in the CO2 formation spectrum; P1– (around 420 K), P2– (~370 K), P3– (~300 K), P4– (~230 K), and P5–CO2 (~170 K). The translational temperature of each CO2 is much higher than the corresponding surface temperature, and increases in the sequence of P1– <P2– <P3– <P4– <P5–CO2. It decreases rapidly with an increase in the desorption angle perpendicular to the surface trough and more slowly parallel to it. This anisotropy is correlated to the reaction site symmetry

Chemical bond elongation following core-excitation of ammonia : resonant Auger spectra calculation

Theoretical resonant Auger decay spectra of ammonia with core-hole excited state dynamics simulation were investigated and some specific features of the experiment, except for a vibrational structure, were reproduced. A power spectral analysis with short-time maximum entropy method has been applied, and an obtained vibrational spacing assigned to the NH stretching mode was 340 meV, which was consistent with the experiment of 390 +/- 10 meV. Proton dynamics of ammonia on the first core-excited state was discussed

Short-time Maximum Entropy Method Analysis of Molecular Dynamics Simulation: Unimolecular Decomposition of Formic Acid

We performed spectral analysis by using the maximum entropy method instead of the traditional Fourier transform technique to investigate the short-time behavior in molecular systems, such as the energy transfer between vibrational modes and chemical reactions. This procedure was applied to direct ab initio molecular dynamics calculations for the decomposition of formic acid. More reactive trajectories of dehydrolation than those of decarboxylation were obtained for Z-formic acid, which was consistent with the prediction of previous theoretical and experimental studies. Short-time maximum entropy method analyses were performed for typical reactive and nonreactive trajectories. Spectrograms of a reactive trajectory were obtained; these clearly showed the reactant, transient, and product regions, especially for the dehydrolation path

Theoretical study of the X-ray absorption spectra of small formic acid clusters

X-ray absorption spectra of small formic acid clusters, (HCOOH)n, n=1-4, were examined theoretically within the framework of density functional theory. For monomer, assignment of the first peak around 532 eV was consistent with the experiment, whereas the second peak around 535 eV was assigned to a mixture of three bands, O1s (C=O) →σ*(OH), O1s (OH) →π*(OH), and O1s (OH) →σ*(OH) excitations. For the dimer, relative intensities of the oscillator strengths of O1s (C=O) and O1s (OH) →σ*(OH) excitations decrease due to strong hydrogen bond formation, whereas those of O1s (C=O) and O1s (OH) →π*(C=O) excitations are insensitive to the dimerization