Resonance Raman Scattering Spectra Research Articles

Resonance Raman Scattering Spectra of Co(II)- and Cu-5,10,15,20-Tetrakis[4-(N-methylpyridyl)]porphyrin in the dd Excited State and Mechanisms of Its Deactivation in a Solution and in Complexes with DNA

Resonance Raman scattering (RRS) spectra of the complexes of 5,10,15,20-tetrakis[4-(N-methylpyridyl)]porphyrin with Co(II) and Cu(II) (CoIITMpyP4 and CuTMpyP4) in various solvents and in complexes with DNA are studied. Under nanosecond pulsed excitation, additional lines have been found in the RRS spectra of CoIITMpyP4 in a dimethylformamide (DMF) solution containing formic acid as an impurity and in a complex with DNA. At the same time, such lines are absent in the spectra of CoIITMpyP4 in pure DMF, dimethyl sulfoxide, water, and alcohols under the same excitation conditions. To interpret the experimental data, we have calculated the structure and vibrations of the solvate complexes of CoIITMpyP4 and CuTMpyP4 with water, methanol, and formic acid in the ground and in excited states. Based on the obtained data, additional lines in the Raman spectra are assigned to the dd excited state corresponding to the d(z2) → d(x2 – y2) transition, the lifetime of which increases with the formation of complexes of CoIITMpyP4 with formic acid. According to the calculation results, this correlates with a decrease in rate constant kic of the internal conversion due to an increase in energy gap ΔE between the ground and dd states of CoIITMpyP4. A decrease in the kic value in the case of binding of CoIITMpyP4 and CuTMpyP4 to DNA is caused by the additional interaction of the extra-ligand water molecule with one of its bases directly or via several water molecules immobilized on DNA surface. This complicates the conformational rearrangement of the water molecule in the dd excited state, which gives rise to an increase in the ΔE value.

Спектры РКР Co(II)- и Cu-5,10,15,20-тетракис[4-(N-метилпиридил)]порфирина в возбужденном dd-состоянии и механизмы его дезактивации в растворе и комплексах с ДНК

A study of the resonance Raman scattering (RRS) spectra of Co(II)- and Cu-5,10,15,20-tetrakis [4-(N-methylpyridyl)]porphyrin (CoIITMpyP4, CuTMpyP4) in various solvents and in complex with DNA was carried out. Additional lines were found in the RRS spectra of CoIITMpyP4 in a dimethylformamide (DMF) solution containing formic acid as an impurity, as well as for its complex with DNA under nanosecond pulsed excitation. At the same time, under the same excitation conditions, such lines are absent in the spectra of CoIITMpyP4 solutions in pure DMF, dimethyl sulfoxide, water, and alcohols. To interpret the experimental data, we performed calculations of the structure and vibrations for the solvate complexes of CoII - and CuTMpyP4 with water, methanol and formic acid in the ground and in excited states. Based on the data obtained, additional lines in the Raman spectra were assigned to the excited dd-state corresponding to the d(z2) d(x2-y2) transition, the lifetime of which increases with the formation of complexes of CoIITMpyP4 with formic acid. According to the calculation results, this correlates with a decrease in the rate constant of the internal conversion kic due to an increase in the energy gap E between the ground and dd states of CoIITMpyP4. In the case of CoII and CuTMpyP4 binding to DNA, the decrease in kic is due to the additional interaction of the extra-liganding water molecule directly or with the participation of several immobilized DNA water molecules with one of its bases. This complicates the conformational rearrangement of the water molecule in the dd-state, which contributes to an increase in E.

Long time aging effect on Be-implanted GaN epitaxial layer

Be-implanted GaN thin films grown by low-pressure Metalorganic Chemical Vapor Deposition (LP-MOCVD), the postimplantation rapid thermal annealing (RTA) samples and the postimplantation RTA samples after 18 years’ room temperature (RT) aging were investigated by Resonant Raman scattering (RRS). It was observed that the Resonant Raman scattering intensity is most enhanced in the 4th order A1 (LO) mode in the after aging sample rather than both the 4th and 5th order A1(LO) mode at different temperatures in the postimplantation RTA sample, which is attributed to a different prominent laser excited emission involved in the RRS processes in the sample before and after aging. A jump step of the intensities of RRS modes was observed at 170 K. Based on the temperature dependent and power dependent RRS spectra, we estimate quantitatively the properties of the optical emission participated in RRS processes below and above this temperature, with the assumption that the intensity of the RRS modes is linearly proportional to the intensity of the optical emission involved in it. We obtained the activation energy of 65 meV and 85 meV for two emissions, respectively, and confirmed both emissions are not band edge related emission with power density dependent RRS spectra. We proposed the dominant optical emission changed from band edge emission to dopant related emission after aging. This study provides an evidence of evolution of optical properties and microstructures in postimplantation RTA GaN epilayers over long time RT aging, which could be a benefit to studying reliability control of devices based on this material.

RRS Spectra and Mechanisms for β-Nitro-Tetraphenylporphyrin Fluorescence Quenching

The study of the excited states and photophysical characteristics of β-nitro-tetraphenylporphyrin (TPP–NO2) has been carried out using resonance Raman scattering (RRS) spectroscopy and methods of the density functional theory. The appearance of new lines, the intensity of which depends on the composition of the matrix and excitation wavelength, has been found in the TPP–NO2 RRS spectra in the low-temperature matrix. The calculation of the vibrational states of TPP–NO2 allowed the linking of the additional lines with the asymmetric vibrations of the nitro group and valence C–C vibrations of the phenyl ring (Ph1) that was nearest to it. The activation of these modes is related to the specific features of the TPP–NO2 geometry in the charge transfer (CT) state from Ph1 to the porphyrin macrocycle. It has been concluded on the basis of the analysis of the data of the study of the RRS spectra and the results of calculations that use the СAM-B3LYP and wB97XD functionals that the CT states do not play a significant role in the TPP–NO2 fluorescence quenching, as previously assumed. The fluorescence quenching owes to strengthening channels of internal and inter-conversion by reducing the energy gaps ΔE(S1 – T1) and ΔE(S1 – S0) as well as increasing the spin-orbit coupling between the S1 and T1 states. It has been shown that TPP–NO2 is characterized by conformational heterogeneity both in the ground and in the excited states, which explains the absence of the monoexponentiality of fluorescence decay kinetics.

Спектры РКР и механизмы тушения флуоресценции beta-нитро-тетрафенилпорфирина

AbstractThe study of the excited states and photophysical characteristics of β-nitro-tetraphenylporphyrin (TPP–NO_2) has been carried out using resonance Raman scattering (RRS) spectroscopy and methods of the density functional theory. The appearance of new lines, the intensity of which depends on the composition of the matrix and excitation wavelength, has been found in the TPP–NO_2 RRS spectra in the low-temperature matrix. The calculation of the vibrational states of TPP–NO_2 allowed the linking of the additional lines with the asymmetric vibrations of the nitro group and valence C–C vibrations of the phenyl ring (Ph1) that was nearest to it. The activation of these modes is related to the specific features of the TPP–NO_2 geometry in the charge transfer (CT) state from Ph1 to the porphyrin macrocycle. It has been concluded on the basis of the analysis of the data of the study of the RRS spectra and the results of calculations that use the СAM-B3LYP and wB97XD functionals that the CT states do not play a significant role in the TPP–NO_2 fluorescence quenching, as previously assumed. The fluorescence quenching owes to strengthening channels of internal and inter-conversion by reducing the energy gaps Δ E ( S _1 – T _1) and Δ E ( S _1 – S _0) as well as increasing the spin-orbit coupling between the S _1 and T _1 states. It has been shown that TPP–NO_2 is characterized by conformational heterogeneity both in the ground and in the excited states, which explains the absence of the monoexponentiality of fluorescence decay kinetics.

Exploratory methodology for retrieving oxidation state information from X-ray resonant Raman scattering spectrometry.

It has been observed recently that the resonant Raman scattering (RRS) peak of an X-ray spectrum contains information about the chemical environment of the irradiated matter. This information is extracted with complex processing of the spectrum data. Principal component analysis (PCA) is a statistical multivariate technique that allows exploring the variance-covariance structure of a set of data, through a few linear combinations of the original variables. This methodology can be applied to obtain information from RRS spectra. To analyze its potentiality, several measurements of different oxides in surface nanolayers were measured in total reflection conditions using synchrotron radiation. Multivariate analysis techniques, in particular, PCA, were used to obtain the information encrypted in the RRS peak, and to establish a new methodology, simpler and more accurate. The results show that multivariate analysis techniques are suitable for the analysis of this kind of spectra, foreseeing its application in future research.

Raman scattering signatures of the unusual vibronic interaction of molecules in liquid helium-3

Light scattering in quantum liquid helium-3 may involve a unique mechanism – the creation and annihilation of atom excitations across the Fermi level. The density of states of particle–hole excitations in the low-energy limit is strongly enhanced as compared to that of collective excitations of phonons in helium-3. This makes possible to directly observe Fermi excitations in the resonant Raman scattering (RRS) by 3He droplets doped by impurity molecules. The RRS spectra essentially depend on the excitation frequency. In case of excitation in the anti-Stokes side of absorption the first order RRS is directly determined by the particle–hole excitations in the vicinity of the impurity molecule and the contribution of phonons mainly given by the localized spherical vibration. The calculations are made for a 3He droplet doped by a glyoxal molecule.

Comparison of SERRS and RRS excitation profiles of [Fe(tpy)2]2+(tpy = 2,2':6',2''‐terpyridine) supported by DFT calculations: effect of the electrostatic bonding to chloride‐modified Ag nanoparticles on its vibrational and electronic structure

Nonresonance (or normal) Raman scattering (NRS), resonance Raman scattering (RRS), surface‐enhanced Raman scattering (SERS), and surface‐enhanced RRS (SERRS) spectra of [Fe(tpy)2]2+complex dication (tpy = 2,2':6',2''‐terpyridine) are reported. The comparison of RRS/NRS and SERRS/SERS excitation profiles of [Fe(tpy)2]2+spectral bands in the range of 445–780 nm is supported by density functional theory (DFT) calculations, Raman depolarization measurements, comparison of the solid [Fe(tpy)2](SO4)2and solution RRS spectra, and characterization of the Ag nanoparticle (NP) hydrosol/[Fe(tpy)2]2+SERS/SERRS active system by surface plasmon extinction spectrum and transmission electron microscopy image of the fractal aggregates (D = 1.82). By DFT calculations, both the Raman active modes and the electronic states of the complex have been assigned to the symmetry species of the D2dpoint group. It has been demonstrated that upon the electrostatic bonding of the complex dication to the chloride‐modified Ag NPs, the geometric and ground state electronic structure of the complex and the identity of the three different metal‐to‐ligand charge transfer (1MLCT) electronic transitions remain preserved. On the other hand, the effect of ion pairing manifests itself by a slight change in localization of one of the electronic transitions (with max. at 552 nm) as well as by promotion of the Herzberg–Teller activation of E modes resulting from coupling of E and B2excited electronic states. Finally, the very low, 1 × 10−11 M SERRS spectral detection limit of [Fe(tpy)2]2+at 532‐nm excitation is attributed to a concerted action of the electromagnetic and molecular resonance mechanism, in conjunction to the electrostatic bonding of the complex dication to the chloride‐modified Ag NP surface. Copyright © 2014 John Wiley & Sons, Ltd.

Simulating One-Photon Absorption and Resonance Raman Scattering Spectra Using Analytical Excited State Energy Gradients within Time-Dependent Density Functional Theory.

A parallel implementation of analytical time-dependent density functional theory gradients is presented for the quantum chemistry program NWChem. The implementation is based on the Lagrangian approach developed by Furche and Ahlrichs. To validate our implementation, we first calculate the Stokes shifts for a range of organic dye molecules using a diverse set of exchange-correlation functionals (traditional density functionals, global hybrids, and range-separated hybrids) followed by simulations of the one-photon absorption and resonance Raman scattering spectrum of the phenoxyl radical, the well-studied dye molecule rhodamine 6G, and a molecular host-guest complex (TTF⊂CBPQT(4+)). The study of organic dye molecules illustrates that B3LYP and CAM-B3LYP generally give the best agreement with experimentally determined Stokes shifts unless the excited state is a charge transfer state. Absorption, resonance Raman, and fluorescence simulations for the phenoxyl radical indicate that explicit solvation may be required for accurate characterization. For the host-guest complex and rhodamine 6G, it is demonstrated that absorption spectra can be simulated in good agreement with experimental data for most exchange-correlation functionals. However, because one-photon absorption spectra generally lack well-resolved vibrational features, resonance Raman simulations are necessary to evaluate the accuracy of the exchange-correlation functional for describing a potential energy surface.

Detection of Nano-Oxidation Sites on the Surface of Hemoglobin Crystals Using Tip-Enhanced Raman Scattering

Hemoglobin nanocrystals were analyzed with tip-enhanced Raman scattering (TERS), surface-enhanced resonance Raman scattering (SERRS) and conventional resonance Raman scattering (RRS) using 532 nm excitation. The extremely high spatial resolution of TERS enables selective enhancement of heme, protein, and amino acid bands from the crystal surface not observed in the SERRS or RRS spectra. Two bands appearing at 1378 and 1355 cm(-1) assigned to the ferric and ferrous oxidation state marker bands, respectively, were observed in both TERS and SERRS spectra but not in the RRS spectrum of the bulk sample. The results indicate that nanoscale oxidation changes are occurring at the hemoglobin crystal surface. These changes could be explained by oxygen exchange at the crystal surface and demonstrate the potential of the TERS technique to obtain structural information not possible with conventional Raman microscopy.

Resonant Raman scattering in CdSxSe1−xnanocrystals: effects of phonon confinement, composition, and elastic strain

AbstractOptical phonon modes, confined in CdSxSe1−xnanocrystal (NC) quantum dots (≈2 nm in radius) grown in a glass matrix by the melting‐nucleation method, were studied by resonant Raman scattering (RRS) spectroscopy and theoretical modeling. The formation of nanocrystalline quantum dots (QDs) is evidenced by the observation of absorption peaks and theoretically expected resonance bands in the RRS excitation spectra. This system, a ternary alloy, offers the possibility to investigate the interplay between the effects of phonon localization by disorder and phonon confinement by the NC/matrix interface. Based on the concept of propagating optical phonons, which is accepted for two‐mode pseudo‐binary alloys in their bulk form, we extended the continuous lattice dynamics model, which has successfully been used for nearly spherical NCs of binary materials, to the present case. After determining the alloy composition for NCs (that was evaluated with only 2–3% uncertainty using the bulk longitudinal optical phonon wavenumbers) and the NC size (using atomic force microscopy and optical absorption data), the experimental RRS spectra were described rather well by this theory, including the line shape and polarization dependence of the scattering intensity. Even though the presence of a compressive strain in the NCs (introduced by the matrix) masks the expected downward shift owing to the phonons' spatial quantization, the asymmetric broadening of both Raman peaks is similar to that characteristic of NCs of pure binary materials. Although with some caution, we suggest that both CdSe‐like and CdS‐like optical phonon modes indeed are propagating within the NC size unless the alloy is considerably heterogeneous. Copyright © 2011 John Wiley & Sons, Ltd.

Effective Time-Independent Calculations of Vibrational Resonance Raman Spectra of Isolated and Solvated Molecules Including Duschinsky and Herzberg-Teller Effects.

We present a method of modeling vibrational resonance Raman scattering (RRS) spectra of isolated and solvated systems with the inclusion of Franck-Condon (FC) and Herzberg-Teller (HT) effects and a full account for possible differences between the harmonic potential energy surfaces of the initial and resonant electronic states. It describes fundamentals, overtones, and combination bands and computes the RRS spectrum as a two-dimensional function of the incident and scattered frequencies. The theoretical foundations of the method are described and the differences with other currently available methodologies are outlined. Applications to the phenoxyl radical in the gas phase and indolinedimethine-malononitrile (IDMN) in acetonitrile and cyclohexane solution are reported, as well as comparisons with available experimental data.

Study of the interaction between cardiolipin bilayers and methylene blue in polymer-based Layer-by-Layer and Langmuir films applied as membrane mimetic systems

An increase of the reports involving mimetic systems has been observed. Briefly, these systems use biological phospholipids to exploit specific interactions between membrane-models and drugs. Here, the Layer-by-Layer (LbL) and Langmuir techniques were used to investigate the interaction between cardiolipin (CLP—negative phospholipid) and a cationic-like drug methylene blue (MB). Supported by a cationic polyelectrolyte (PAH), LbL films containing PAH/(CLP + MB) and PAH/(CLP + MB + AgNP) were grown up to 14 bilayers. The optical microscopy analysis revealed a decrease of the CLP vesicle sizes in the presence of MB as a possible consequence of the MB action onto the mechanical properties of the CLP membrane. From FTIR spectra, changes mainly related to peak position and band intensity and shape were observed in the spectra from PAH/CLP when in the presence of MB. The latter supports that the interactions between the phosphate and amine charged groups from CLP and PAH, respectively, established during the LbL film fabrication, besides the CLP hydrocarbon environment, are influenced by the presence of MB. Using the micro-Raman technique, a chemical mapping was build based on MB spectrum by resonance Raman scattering (RRS) and surface-enhanced resonance Raman scattering (SERRS). The later phenomenon was activated by Ag nanoparticles (AgNPs) trapped within the LbL film allowing collecting spectra for a single bilayer of PAH/(CLP + MB + AgNP). A rough estimation showed a SERRS amplification of 10 3 in comparison to RRS spectra. As a complementary approach, Langmuir films of CLP in the presence of co-spread MB were investigated through surface pressure vs mean molecular area ( π– A) isotherms. The results showed that for concentrations of MB below 100 mol%, the drug is expelled to water subphase for high values of surface pressure (condensed phase). For concentration at 100% and higher, the MB keeps bound to CLP floating monolayer.

Determination of Binding Strengths of a Host−Guest Complex Using Resonance Raman Scattering

The detection of analyte-binding events by receptors is drawing together the fields of Raman spectroscopy and supramolecular chemistry. This study is intended to facilitate this cohering by examining a model in the solution phase. The resonance Raman scattering (RRS) spectra of the complexation between tetrathiafulvalene (TTF) and cyclobis(paraquat-p-phenylene) (CBPQT(4+)) has been used as the model system to characterize the binding event of a host-guest system. RRS spectra are generated by excitation (lambda(exc) = 785 nm) within the lowest-energy charge-transfer (CT) transition (lambda(max) = 865 nm) of the TTF subsetCBPQT(4+) complex. The paired binding curves from the RRS and UV-vis-NIR titration data agrees with prior work, and a DeltaG of -5.7 +/- 0.6 kcal mol(-1) (MeCN, 298 K) was obtained for the complexation of TTF with CBPQT(4+). Computations on the complex and its components reproduce the energy shifts and resonance enhancements of the Raman band intensities, providing a basis to identify the structural and vibrational changes occurring upon complexation. The changes in bond lengths coincide with partial depopulation of a TTF-based HOMO and population of a CBPQT(4+)-based LUMO through CT mixing in the ground state of 0.46e(-). The structural changes upon complexation generally lead to lower wavenumber vibrations and to changes in the normal mode descriptions.

Species enrichment of SWNTs with pyrene alkylamide derivatives: is the alkyl chain lengthimportant?

Three similar amide-functionalized pyrene derivatives (N-methyl(18-Crown-6)pyrene1-acetamide,N-methyl(18-Crown-6)pyrene-1-butyramide andN-methyl (18-Crown-6)pyrene-1-formamide), denoted as pa-18-C-6, pb-18-C-6 and pc-18-C-6,respectively, with different alkyl chain lengths between the amide groups and pyrenemoieties have been successfully synthesized and for the first time, their separation effectson single-walled carbon nanotubes (SWNTs) according to their electronic structures(metallic/semiconducting) and diameter have been demonstrated. Resonant Ramanspectroscopy and UV–vis–NIR show that all three pyrene derivatives are selective to metallicSWNTs (met-SWNTs). Resonant Raman scattering (RRS) spectra also indicate that twoof the pyrene derivatives, pb-18-C-6 and pc-18-C-6, are selective to large-diameter (D>1 nm) met-SWNTs. The third compound, pa-18-C-6, is selective to small-diameter (D<1.03 nm) met-SWNTs due to the ketone-to-enol rearrangement resulting in higher strain forcerelaxation; the rearrangement was shown by Fourier-transform infrared spectroscopy data.For their discrimination between different relatively large-diameter semiconducting species,RRS spectra using a 785 nm laser show that pb-18-C-6 is selective to larger diameter oneswhile pa-18-C-6 and pc-18-C-6 have no selectivity. The selectivity for met-SWNTs in thesolution is confirmed by a tenfold decline in thin film SWNT network resistivity (from 43 to4.3 S m−1) after depletion of metallic nanotubes by a four-pass selection procedure usingpa-18-C-6 and pc-18-C-6 surfactants alternately. Further, after the four-pass selectionprocedure, the conductivity of a network using the supernatant SWNTs changes lesswhen heated in air compared to another network using the precipitated SWNTs;the high conductivity stability of the network with supernatant SWNTs furtherconfirms the high content of met-SWNTs which are resistant to carrier doping.

Electronic states of trans-polyacetylene, poly( p-phenylene vinylene) and sp-hybridised carbon species in amorphous hydrogenated carbon probed by resonant Raman scattering

Inclusions of sp-hybridised, trans-polyacetylene [ trans-(CH) x ] and poly( p-phenylene vinylene) (PPV) chains are revealed using resonant Raman scattering (RRS) investigation of amorphous hydrogenated carbon ( a-C:H) films in the near IR – UV range. The RRS spectra of trans-(CH) x core A g modes and the PPV CC–H phenylene mode are found to transform and disperse as the laser excitation energy ℏ ω L is increased from near IR through visible to UV, whereas sp-bonded inclusions only become evident in UV. This is attributed to ℏ ω L probing of trans-(CH) x chain inhomogeneity and the distribution of chains with varying conjugation length; for PPV to the resonant probing of phelynene ring disorder; and for sp segments, to ℏ ω L probing of a local band gap of end-terminated polyynes. The IR spectra analysis confirmed the presence of sp, trans-(CH) x and PPV inclusions. The obtained RRS results for a-C:H denote differentiation between the core A g trans-(CH) x modes and the PPV phenylene mode. Furthermore, it was found that at various laser excitation energies the changes in Raman spectra features for trans-(CH) x segments included in an amorphous carbon matrix are the same as in bulk trans-polyacetylene. The latter finding can be used to facilitate identification of trans-(CH) x in the spectra of complex carbonaceous materials.

Size effects on Raman spectra of small CdSe nanoparticles in polymer films

The results of a resonant Raman scattering (RRS) study of polymer-stabilized colloidalCdSe nanoparticles (NPs) are reported. The size-selective nature of the RRS isdemonstrated by analysing the NP ensembles with different average size and size distribution Δd using a set of excitation wavelengths. The effect of size selection on the estimation of and Δd values from the RRS spectra is discussed, as well as some peculiarities of RRS onsurface optical phonons. From the experimentally observed small variation of theI2LO/ILO ratio for 2–5 nm NPs a minor effect of on the electron–phonon coupling strength in this range is supposed.

SERRS study of [Ru(CN)5(pyS)]4− SAM and cytochrome c: A suggestion toward the heterogeneous molecular recognition

Surface-Enhanced Raman Scattering (SERS) spectra of [Ru(CN)5(pyS)]4− (RupyS) complex self-assembled monolayer (SAM) were obtained on gold and silver surfaces at 632.8 and 413.1 nm excitation radiations, respectively. The bands assigned to the heme iron of the cytochrome c (cyt c) metalloprotein group were observed by using the RupyS SAM on silver at 413.1 nm. The Surface-Enhanced Resonance Raman Scattering (SERRS) spectra of the RupyS SAM on silver in the cyt c solution obtained at −0.2 and +0.2 V present bands at 1,365 and 1,374 cm−1 characteristic of the heme group, indicating the reduced and oxidized states of this protein, respectively. The bands observed at 1,464, 1,504, and 1,638 cm−1 are used to confirm the redox state of cyt c. The presence of the oxidized and reduced bands in function of different applied potential is an evidence that the protein is interacting with the modifier.

High-resolution study of the x-ray resonant Raman scattering process around the1sabsorption edge for aluminium, silicon, and their oxides

X-ray resonant Raman scattering (RRS) spectra of Al, ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, Si, and $\mathrm{Si}{\mathrm{O}}_{2}$ were measured at the European Synchrotron Radiation Facility, using a high-resolution Bragg-type curved crystal spectrometer. The x-ray RRS spectra were collected at several beam energies tuned below the $1s$ absorption thresholds of Al and Si. Differences in the spectral features between the elemental samples and the oxide ones were clearly observed. The data were interpreted using the second-order perturbation theory within the Kramers-Heisenberg (KH) approach. It is shown that, using the KH formalism, oscillator strengths that are similar to the ones deduced from x-ray absorption measurements can be extracted from emission x-ray RRS spectra. The total cross sections for the x-ray RRS process were derived for the different photon beam energies and compared with theoretical predictions. For elemental silicon, the weak $1s\text{\ensuremath{-}}3p$ excitation was observed and found to be consistent with results of density of states calculations.

High-Resolution Study of X-Ray Resonant Raman Scattering at theKEdge of Silicon

We report on the first high-resolution measurements of the K x-ray resonant Raman scattering (RRS) in Si. The measured x-ray RRS spectra, interpreted using the Kramers-Heisenberg approach, revealed spectral features corresponding to electronic excitations to the conduction and valence bands in silicon. The total cross sections for the x-ray RRS at the 1s absorption edge and the 1s-3p excitation were derived. The Kramers-Heisenberg formalism was found to reproduce quite well the x-ray RRS spectra, which is of prime importance for applications of the total-reflection x-ray fluorescence technique.