T. Gejo

Characterization of Hard Diamond-Like Carbon Films Formed by Ar Gas Cluster Ion Beam-Assisted Fullerene Deposition

The coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. With attention to the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital, relative sp2 contents of various DLC films were estimated. The sp2 contents of the DLC films formed by the GCIB-assisted deposition were observed to be lower than those of the DLC films formed by other methods. The hardness value measured with a nano-indentation technique was found to be strongly related to the sp2 content of the DLC film.

Photodissociation of ozone in the Hartley band: Fluctuation of the vibrational state distribution in the O2(1Δg) fragment

The photodissociation of O3 in the Hartley band has been investigated by high‐resolution photofragment translational spectroscopy (PTS). At λdiss=248 nm we determined the quantum yield of the dominant decay channel leading to O2(1Δg)+O(1D) and the fragment vibrational state distribution. The fragment recoil anisotropy (β=1.25±0.15) was found to be independent of the fragment vibrational states. Between λdiss=275 and 295 nm β assumes a value of 1.6±0.2, which exceeds the value expected for a simple impulsive process. Photofragment yield measurements carried out by PTS between 272 and 286 nm revealed a strong fluctuation of the vibrational state distribution with λdiss. Based on the small but distinct structure superimposed on the broad continuum of the Hartley band and the findings of recent 3D wave packet calculations, we propose this fluctuation, a manifestation of wavelength‐dependent partial cross sections, to arise predominantly from an interference effect. The latter occurs between the part of the in...

Quantum beats in the S1 dynamics of acetaldehyde

Abstract We have investigated jet-cooled acetaldehyde, CH 3 CHO and CD 3 CDO, excited to the S 1 (nπ ∗ ) singlet state. For excess energies Δ E (S 1 ) = 1500–2000 cm −1 , we observed fluorescence decays with superimposed quantum beats due to coherently excited S 1 –T 1 eigenstates and an increase in the decay rates parallelled by a decrease in the fluorescence, most dramatic at Δ E (S 1 ) ≈ 2000 cm −1 . These results show that S 1 –T 1 intersystem crossing is not a dissipative process up to the fluorescence breakdown. It is proposed that at this energy the continuum for α-cleavage in the T 1 state is reached which causes the S ⇝ T 1 intersystem crossing to become the dominant deactivation pathway.

Angle-resolved photoion spectroscopy of NO2 and SO2

Abstract Based on recent conceptual and technological improvements for soft X-ray monochromators, a varied-line-spacing plane grating monochromator of the Hetrrick type is installed on the bending-magnet beamline BL4B in the UVSOR facility with a second generation VUV ring of the beam energy of 0.75 GeV. The BL4B has enabled us to realize various spectroscopic investigations under high resolution conditions in the energy range of 90–800 eV. High-resolution angle-resolved photoion-yield spectra (ARPIS) of NO2 and SO2 have been measured in the N and O K-shell excitation regions. The fragment-ion yield spectra measured at 0° and 90° relative to the electric vector of the light reveal excitation symmetries of complicated electronic states. The spectral features are interpreted in comparison with other transition systems, and quantum chemical calculations show strong or weak Rydberg-valence mixing depending on the excitation site in the molecule.

Hydrogen bonding in methanol clusters probed by inner-shell photoabsorption spectroscopy in the carbon and oxygen K-edge regions

Hydrogen bonding in methanol clusters has been investigated by using inner-shell photoabsorption spectroscopy and density functional theory (DFT) calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of H(CH(3)OH)(n)(+) were measured as the soft x-ray absorption spectra of methanol clusters. The first resonance peak in the PIY curves, which is assigned to the sigma*(O-H) resonance transition, exhibits a 1.20 eV blueshift relative to the total-ion-yield (TIY) curves of molecular methanol in the oxygen K-edge region, while it exhibits a shift of only 0.25 eV in the carbon K-edge region. Decreased intensities of the transitions to higher Rydberg orbitals were observed in the PIY curves of the clusters. The drastic change in the sigma*(O-H) resonance transition is interpreted by the change in the character of the sigma*(O-H) molecular orbital at the H-donating OH site due to the hydrogen-bonding interaction.

From the operation of an SRFEL to a user facility

Storage ring free-electron lasers (SRFELs) likely have a potentiality for scientific application as a unique light source because of the good coherence and temporal feature in addition to variable wavelength. At the UVSOR, the performance of the SRFEL has been improved aiming at users applications. Recently, an experiment using SRFEL combined with synchrotron radiation (SR) was begun. As the first experiment, the double-resonant excitation of Xe has been investigated by using SR and SRFEL as pump and probe lights, respectively. The relevance of making use of SRFEL for the pump/probe experiment is demonstrated.

Hydrogen bonding in acetone clusters probed by near-edge x-ray absorption fine structure spectroscopy in the carbon and oxygen K-edge regions

Hydrogen bonding in acetone clusters was investigated using near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of the cluster ions were measured as the NEXAFS spectra of acetone clusters. In the carbon K-edge region, the first resonance peak, which was assigned to the C(CO) 1s-->pi( *)(C=O) resonance transition, showed no substantial change in the PIY curves of the acetone clusters, while the C(CH3) 1s-->3ppi(CH(3)) excitation feature was found to be strongly suppressed. The selective suppression of the C(CH3) 1s-->3ppi(CH(3)) resonance transition can be explained by the change in the character of the 3ppi(CH(3)) orbital due to the C=O...H-C type of hydrogen-bonding interaction. On the other hand, the NEXAFS spectra of the acetone molecule and clusters were almost identical in the oxygen K-edge region, except for a small shift in the pi( *)(C=O) resonance of 0.13 eV, because the character of the pi( *)(C=O) orbital remained, regardless of the C=O...H-C hydrogen bonding interaction.

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. Cluster-specific excitation spectra have been generated by monitoring the partial ion yields of the product cations. Resonance transitions of O1s(C[double bond]O/OH) electrons into pi(CO)* orbital in the preedge region were found to shift in energy upon clusterization. A blueshift of the O1s(C[double bond]O)-->pi(CO)* transition by approximately 0.2 eV and a redshift of the O1s(OH)-->pi(CO)* by approximately 0.6 eV were observed, indicative of strong hydrogen-bond formation within the clusters. The results have been compared with a recent theoretical calculation, which supports the conclusion that the formic-acid clusters consist of the most stable cyclic dimer andor trimer units. Specifically labeled formic acid-d, HCOOD, was also used to examine the core-excited fragmentation mechanisms. These deuterium-labeled experiments showed that HDO+ was formed via site-specific migration of a formyl hydrogen within an individual molecule, and that HD2O+ was produced via the subsequent transfer of a deuterium atom from the hydroxyl group of a nearest-neighbor molecule within a cationic cluster. Deuteron (proton) transfer from the hydroxyl site of a hydrogen-bond partner was also found to take place, producing deuteronated HCOOD.D+ (protonated HCOOH.H+) cations within the clusters.

Molecular size effect on the site-specific fragmentation of N and O K shell excited CH3OCOCN and CH3OCOCH2CN molecules

Abstract The effect of molecular size on the site-specific fragmentation was investigated by exciting the N and O K shells of methyl cyanoformate (CH 3 OCOCN) and methyl cyanoacetate (CH 3 OCOCH 2 CN). The fragmentation patterns were essentially identical in the N and O core excitations of CH 3 OCOCN. Site and state dependent fragmentation was clearly observed in the core hole CH 3 OCOCH 2 CN: The fragment ions mainly observed at the O K edge excitation were CH 3 + , HCO + , CH 2 CN + , CH 3 OCO + , and COCH 2 CN + . At the N(1s) excitation the large CH 3 OCO + and COCH 2 CN + fragments were extremely depressed, and alternatively the small CH 3 + , HCO + , and CH 2 CN + ions were dominant. Especially at the π* CN ←N(1s) resonance transition the N + and CO + fragment ions were exclusively produced with yields of 40 and 15%, respectively. The total photoabsorption cross sections were measured in the N and O K regions and the observed peaks were tentatively assigned. Reflectron type time-of-flight mass spectrometry was employed to attain the mass separation M /Δ M ≥100 at M/e ≈100 for the core excited molecules ejecting fragments with considerable kinetic energies.

NEXAFS study on substrate temperature dependence of DLC films formed by Ar cluster ion beam assisted deposition

Abstract For the optimization of the synthesis condition of the production of diamond-like carbon (DLC) thin films by Ar gas cluster ion beam (GCIB) assisted deposition of fullerene, the local structure of DLC thin films was investigated by measuring near-edge X-ray absorption fine structure spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. The DLC thin films were formed by GCIB assisted deposition at substrate temperatures ranging from room temperature to 250 °C. The sp2 content estimated from the analysis of the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital was found to increase with the substrate temperature during GCIB assisted deposition.