Search results for "Spectral"
showing 10 items of 3116 documents
From Above Threshold Ionization to Statistical Electron Emission: The Laser Pulse-Duration Dependence ofC60Photoelectron Spectra
2000
The photoelectron spectra of C60 ionized using a 790 nm laser with pulse durations varying from 25 fs to 5 ps have been determined. For 25 fs pulses, in the absence of fragmentation, the ionization mechanism is direct multiphoton ionization with clear observation of above threshold ionization. As the pulse duration is increased, this becomes dominated by a statistical ionization due to equilibration among the electronic degrees of freedom. For pulse durations on the order of a ps coupling to the vibrational degrees of freedom occurs and the well-known phenomenon of delayed (ms) ionization is observed.
Electronic and optical properties of InN nanowires
2016
Abstract We have employed a multiband envelope function method to study wurtzite [0001] InN nanowires of cylindrical cross section. The electronic subband structure and optical absorption spectrum are calculated as a function of the nanowire radius. The energies of the Γ -point conduction band states show a monotonous increase with decreasing radius. On the other hand, the size dispersion of the valence band states is more involved, showing various crossing and anticrossing effects due to the interplay between the confinement and band mixing effects. Thus, for small ( R 2 nm ) nanowires the highest valence band state has dominant p z -symmetry, but for R > 2 nm the highest state has dominan…
Al driven peculiarities of local coordination and magnetic properties in single phase Alx CrFeCoNi high entropy alloys
2021
The authors thank the Helmholtz-Zentrum Berlin for the provision of access to synchrotron radiation facilities and allocation of synchrotron radiation at the PM2-VEKMAG, BAMline, and UE46_PGM-1 beamlines of BESSY II at HZB as well as measurement time for magnetometry at HZB CoreLab for Quantum Materials. A. S. acknowledges personal funding from CALIPSOplus project (the Grant Agreement no. 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020). The financial support for the VEKMAG project and the PM2-VEKMAG beamline by the German Federal Ministry for Education and Research (Nos. BMBF 05K10PC2, 05K10WR1, 05K10KE1) and by HZB is cordially acknowledged by all co-author…
Calculation of vibrationally resolved absorption and fluorescence spectra of the rylenes
2020
A generating function method was used to simulate the vibrationally resolved absorption and emission spectra of perylene, terrylene and quaterrylene. This method operates on the basis of adiabatic excitation energies and electronic ground and excited state vibrational frequencies. These parameters were calculated using density functional theory with the PBE0 functional for perylene and terrylene and with the BH-LYP functional for quaterrylene. The vertical excitation energies of the lower excited states were calculated using functionals with differing amounts of Hartree-Fock exchange. The optimal functional for each molecule was chosen by comparing these energies to literature excitation en…
Visible to vacuum-UV range optical absorption of oxygen dangling bonds in amorphous SiO2
2011
Synthetic silica glass with an optical absorption spectrum dominated by oxygen dangling bonds (nonbridging oxygen hole centers, or NBOHCs) and having negligible (1%) contribution from the usually copresent Si dangling bonds (E\ensuremath{'}-centers), was prepared by room temperature ultraviolet photobleaching of high SiOH content (``wet'') silica, irradiated by F${}_{2}$ laser (7.9 eV) at $T$ = 80 K. This allowed us to obtain the up-to-now controversial optical absorption spectrum of NBOHC in the ultraviolet and vacuum-ultraviolet (UV-VUV) region of the spectrum and to show that it is semicontinuous from 4 to 7.8 eV and cannot be represented by a pair of distinct Gaussian bands. Since NBOHC…
Magnetic Properties of Quinoidal Oligothiophenes: More Than Good Candidates for Ambipolar Organic Semiconductors?
2006
A series of quinoidal oligothiophenes have been investigated by means of solid-state Fourier-transform (FT)-Raman and electron spin resonance (ESR) spectroscopies complemented with density functional theory calculations. FT-Raman spectra recorded as a function of temperature show that, upon laser irradiation, the molecules undergo a reversible structural evolution from a quinoid-type pattern at low temperature to an aromatic-type pattern at high temperature. Moreover, ESR spectra show that a portion of these compounds exists in a biradical state at room temperature. These seemingly disconnected findings and others, such as conformational isomerism, are consistently explained by the consider…
The influence of the temperature of insulation oil on the results of measurements of the acoustic emission signals generated by partial discharges
2005
The subject matter of this paper refers to the improvement of the acoustic emission method (AE) used for evaluation of partial discharges (PDs) generated in paper-oil insulation systems of power appliances. The paper presents the measurement and analysis results of the AE signals generated by partial discharges of the surface type (SPDs). The AE signals were measured on the surface of a transformer tub using a broad-band contact transducer, and then they were subject to a time-frequency analysis. The measurements were taken while heating transformer oil in the range from 30 to 85°C with gradation of every 5°C. For time runs, amplitude and energy density spectra the descriptor values that ch…
The methane Raman spectrum from 1200 to 5500 cm(-1): A first step toward temperature diagnostic using methane as a probe molecule in combustion syste…
2005
International audience; We present a study of the spontaneous Raman spectra of (CH4)-C-12 from 1200 to 5500 cm(-1) at various temperatures. This study is of interest from a fundamental as well as from a practical point of view with regards to the temperature diagnostic in hydrocarbon combustion. The present investigation shows that the spontaneous (CH4)-C-12 Raman spectra are very sensitive to temperature and that the complexity of methane spectra is not an obstacle to use methane as a probe molecule in laser-diagnostic techniques. Our study consists in determining the polarisability parameters of methane (CH4)-C-12, unknown at the present time, from spontaneous Raman spectra recorded at pr…
Ion transport in the fragile glass former3KNO3-2Ca(NO3)2
1996
The molten salt ${3\mathrm{K}\mathrm{N}\mathrm{O}}_{3}$-2Ca(${\mathrm{NO}}_{3}$${)}_{2}$ has been studied in the frequency range 5 mHz40 GHz and for temperatures 10 KT500 K using impedance spectroscopy. It is found that in the microwave regime the dynamic conductivity traces the primary response. In the radio- and audio-frequency ranges the mobile ion relaxation becomes increasingly decoupled and the time scale and stretching of the response as determined from electrical modulus spectra differ from those obtained by spectroscopies probing the structural response. For T\ensuremath{\gtrsim}360 K minima are detected in the dielectric loss that make possible a comparison with recent mode-coupli…
High-resolution Raman spectroscopy of the ν1 region and Raman-Raman double resonance spectroscopy of the 2ν1-ν 1 band of 32SF6 and 34SF 6. Determinat…
2004
The ν1 region of 32SF6 and 34SF6 has been studied by stimulated Raman spectroscopy. For both isotopomers, a detailed analysis has been performed. Several hot bands (ν1+ν6-ν6, ν1+2ν 6-2ν6, ν1+ν5-ν 5) have been taken into account to calculate synthetic spectra that satisfactorily reproduce the experimental data. These results, together with the previous studies of the other fundamental bands have allowed us to determine the equilibrium bond length of sulfur hexafluoride as r e=1.5560(1) Å, in very good agreement with recent ab initio calculations. The 2ν1-ν1 band has also been studied for both isotopomers by Raman-Raman double resonance spectroscopy and the resulting spectra have been analyze…