196,347 research outputs found
Electronic structure modifications induced by increased molecular complexity: from triphenylamine to m-MTDATA
No full textThe starburst π-conjugated molecule 4,4′,4′′-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (C57H48N4, m-MTDATA), based on triphenylamine (TPA) building blocks, is widely used in optoelectronic devices due to its good electron-donor characteristics. The electronic structure of m-MTDATA was investigated for the first time in the gas phase by means of PhotoElectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The combination of Density Functional Theory (DFT) calculations with the experimental spectra provides a comprehensive description of the molecular electronic structure. Moreover, by comparing the results with previous TPA measurements, we could shed light on how the electronic structure evolves when the molecular size is increased. We found that the C 1s photoelectron spectra of m-MTDATA and TPA are similar, due to the balance of the counter-acting effects of the electronegativity of the N atoms and the delocalization of the amine lone-pair electrons. In contrast, the increased number of N atoms (i.e. N lone pairs) in m-MTDATA determines a three-peak feature in the outermost valence binding energy region with strong contributions by the N 2pz orbitals. We also obtained a decrease of the HOMO-LUMO gap for m-MTDATA, which points to improved electron donating properties of m-MTDATA with respect to TPA
Soft X-ray photoelectron-photoabsorption spectroscopy and electronic structure of barbituric and 2-thiobarbituric acid.
No full textWe present a combined experimental and theoretical investigation of the electronic spectra of barbituric acid (BA) and 2-thiobarbituric acid (TBA) molecules in the vapour phase. The valence band photoemission and the core level (O, N, C 1s and S 2p) photoemission and photoabsorption
spectra have been measured in the vapour phase using synchrotron light and then assigned with the support of quantum chemical calculations. First the valence band binding energies have been
calculated using the Koopman's approximation at the B3LYP/6- 311++G** level, then the outer valence behaviour has been better approximated with electron propagator calculations (OVGF and P3 approximations), available in the G09 software package. [1] The
core ionized states and core-to-excited states transitions were solved within the Hartree-Fock approximation by explicitly taking into account the core hole, using the GSCF3 code developed by prof. N. Kosugi. [2] The calculations were run for both the tri-keto and the
hydroxy-di-keto form, where the enolization of one of the two
equivalent keto groups is produced by proton transfer from the methylene group, which is more acidic than the NH groups. In agreement with previous ab initio [3, 4] and gas-phase electron
diffraction [5] works, only the tri-keto tautomers have been detected.
[1] Gaussian 09, Revision A.02, M. J. Frisch et al., Gaussian, Inc., Wallingford CT, 2009.
[2] N. Kosugi, and H. Kuroda, Chem. Phys. Lett. 74, 1980, 490. N. Kosugi, and H. Kuroda, Chem. Phys. Lett., 94, 1983, 377. N. Kosugi, Theor. Chim. Acta, 72, 1987, 149.
[3] F. Zuccarello, G. Buemi, C. Gandolfo and A. Contino, Spectrochim Acta A, 59, 2003, 139-151.
[4] E. Méndez, M. F. Cerdá, J. S. Gancheff, J. Torres, C. Kremer, J. Castiglioni, M. Kieninger, and O. N. Ventura, J. Phys. Chem. C, 111, 2007, 3369-3383
[5] O. V. Dorofeeva, I. I. Marochkin, N. M. Karasev, I. F. Shishkov and H. Oberhammer, Structural Chemistry, 22, 2011, 419-42
On the possibility to utilize a PCO Edge 4.2 bi scientific CMOS imager for extended ultra violet and soft X-ray photon detection
No full textA state of the art commercial detector, a PCO Edge 4.2 bi based on a back illuminated sCMOS sensor developed for applications in the visible light/ultra violet regime has been adapted for ultra-high vacuum operations and has been characterized using soft X-ray in the energy range from 30 eV to 1000 eV. The imager features 2048 x 2048 pixel with a pixel size of 6.5 mu m x 6.5 mu m and allows full frame acquisitions at 48 Hz with a dynamic range of 88 dB at a noise level of 1.9 e(-). Spatial resolution and quantum efficiency have been elucidated in the aforementioned energy range at a soft X-ray beam line at Elettra Sincrotrone Trieste. The handiness of the camera as well as its Python library package allows easy and fast integration into the beam line environments of synchrotron sources and free electron lasers
m-MTDATA on Au(111): Spectroscopic Evidence of Molecule-Substrate Interactions
No full textThe starburst π-conjugated molecule based on triphenylamine (TPA) building blocks, 4,4′,4′′-tris(N-3-ethylphenyl-N-phenylamino)triphenylamine (C57H48N4, m-MTDATA), is widely used in optoelectronic devices due to its electron-donating properties. The electronic structure of m-MTDATA adsorbed on an Au(111) surface was investigated by means of photoelectron spectroscopy (PES) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results were further compared to gas-phase measurements and DFT calculations. Our results clearly indicate a significant molecule-substrate interaction that induces considerable modifications on the electronic structure of the adsorbate compared to the isolated molecule. The energy level alignment analysis shows that the HOMO-LUMO gap is filled by new interface states
Coherent Excitation of X-Ray Fluorescence and Interference of Radiation at the Output of Polycapillary Structures
No full textThe diffraction of long-wavelength X rays with the energy corresponding to the region of anomalous dispersion near the Si L2,3 absorption edges transmitted through microchannel plates has been studied both experimentally and theoretically. The radiation of a finite antenna array, as well as the processes of excitation of X-ray fluorescence and propagation of waves in hollow waveguide structures, has been mathematically simulated. The model describes a polycapillary structure consisting of noninteracting emitters, which are hollow channels of a microchannel plate. It has been shown that coherently excited X-ray fluorescence propagates primarily in the direction of the zeroth diffraction order
Comparative Experimental and Theoretical Study of the C and O K-Edge X-ray Absorption Spectroscopy in Three Highly Popular, Low Spin Organoiron Complexes: [Fe(CO)5], [(η5-C5H5)Fe(CO)(μ-CO)]2, and [(η5-C5H5)2Fe]
No full textThe unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)5], [(η5-C5H5)Fe(CO)(μ-CO)]2, and [(η5-C5H5)2Fe]; 0, I, and II, respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L2,3-edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. Inorg. Chem. 2019, 58, 5844). The first-principle simulation of the C and O K-edge features allowed us to univocally identify the electronic states associated to the ligand-to-metal charge transfer (LMCT) transitions both in I and in II. At variance to that, LMCT transitions with sizable oscillator strengths do not play any role in determining neither the C nor the O K-edge spectral pattern of 0. The higher IC-acceptor capability of the CO ligand, regardless of its terminal or bridging coordination, with respect to [(η5-C5H5)]- is herein ultimately confirmed
Comparative Experimental and Theoretical Study of the Fe L-2,L-3-Edges X-ray Absorption Spectroscopy in Three Highly Popular, Low-Spin Organoiron Complexes: [Fe(CO)(5)], [(eta(5)-C5H5)Fe(CO)(mu-CO)](2), and [(eta(5)-C5H5)(2)Fe]
No full textThe occupied and unoccupied electronic structures of three highly popular, closed shell organoiron complexes ([Fe(CO)(5)], [(eta(5)-C5H5 )Fe(CO)(mu-CO)](2), and [(eta(5)-C5H5)(2)Fe]) have been theoretically investigated by taking advantage of density functional theory (DFT) calculations coupled to the isolobal analogy (Elian et al. Inorg. Chem. 1976, 15, 1148). The adopted approach allowed us to look into the relative role played by the ligand -> Fe donation and the Fe -> ligand back-donation in title molecules, as well as to investigate how CO- (terminal or bridging) and [(eta(5)-C5H5)](-)-based pi* orbitals compete when these two ligands are simultaneously present as in [(eta(5)-C5H5)Fe(CO)(mu-CO)](2). Insights into the nature and the strength of the bonding between Fe and the C donor atoms have been gained by exploiting the Nalewajski-Mrozek bond multiplicity index (Nalewajski et al. Int. J. Quantum Chem. 1994, 51, 187), which have been found especially sensitive even to tiny bond distance variations. The bonding picture emerging from ground state DFT results proved fruitful to guide the assignment of original, high-resolution, gas-phase L-2,L-3-edges X-ray absorption spectra of the title molecules, which have been modeled by the two-component relativistic time-dependent DFT including spin orbit coupling and correlation effects and taking advantage of the full use of symmetry. Assignments alternative to those reported in the literature for both [Fe(CO)(5)] and [(eta(5)-C5H5)(2)Fe] are herein proposed. Despite the high popularity of the investigated molecules, the complementary use of symmetry, orbital, and spectroscopy allowed us to further look into the metal-ligand symmetry-restricted-covalency and the differential-orbital covalency, which characterize them
Accessing the fractal dimension of free clusters in supersonic beams
No full textIn this paper a method for the quantitative determination of a morphology descriptor of free clusters with complex nanostructure is presented and applied to transition metal nanoparticles produced by a pulsed vaporization source. The method, which is based on the low-pressure aerodynamic mobility of neutral particles, can be applied as a characterization tool to a broad class of gas-phase nanoparticle sources for on-line investigation of particle growth and for quantifying coalescence versus agglomerate aggregation. We report on the application of this method for the characterization of free titanium clusters produced by a pulsed microplasma cluster source in the size range of approximately 300-6000 atoms. The clusters have an open fractal-like structure, with the fractal dimension depending on their thermal history during growth and evolving towards softer aggregates for longer residence times where lowertemperature conditions characterize the growth environment
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