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Spectra reflecting the formation of single-site double-core-hole pre-edge states involving the N 1s and C 1s core levels of acetonitrile have been recorded by means of high-resolution single-channel photoelectron spectroscopy using hard X-ray excitation. The data are interpreted with the aid of ab initio quantum chemical calculations, which take into account the direct or conjugate nature of this type of electronic states. Furthermore, the photoelectron spectra of N 1s and C 1s singly core-ionized states have been measured. From these spectra, the chemical shift between the two C 1s−1 states is estimated. Finally, by utilizing C 1s single and double core-ionization potentials, initial and final state effects for the two inequivalent carbon atoms have been investigated. [ABSTRACT FROM AUTHOR]

Angle-resolved electron energy-loss spectra have been measured for the methyl methacrylate (MMA) and styrene molecules in the 0 - 50 eV energy range. The spectra have been obtained at 1 keV incident energy, with an energy resolution of 0.8 eV and covering an angular range of 2.0 to 7.0 degrees. Within our knowledge, this is the first gas-phase excitation spectrum for MMA and styrene in this energy range. The spectra of MMA at small scattering angles are dominated by an intense peak at 6.7 eV followed by a broad band centered at about 16 eV. In the case of styrene, six bands can be observed in the spectra. Based on the angular behaviour of the excitation spectra of these molecules, the low-lying peaks observed are considered to be associated predominantly with dipole-allowed processes. In both cases, new bands can be observed for excitation energies greater than 20 eV. This could be associated with dipole-forbidden transitions to shake-up and doubly-excited states.

Molecularly imprinted polymers (MIP) are materials capable of recognizing specific molecules, usually through non-covalent bonds. In this work, gallic acid (GA) was selected as the imprinting molecule, and MIP for GA (MIP-GA) was synthesized by bulk polymerization. X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) confirmed the MIP-GA recognition property. Poly(caprolactone) mat containing MIP-GA particles (MIM-GA) was produced by electrospinning, which was morphologically characterized by Scanning electron microscopy (SEM). Functionalized MIM-GA was obtained by washes sequence in methanol for the GA removal from MIM-GA. The GA removal was confirmed by High-performance liquid chromatography (HPLC) with UV-Vis detection at 214 and 268 nm. The functionalized MIM-GA immersed in GA methanolic solution with a concentration of 1.0 mM extracted 96±1.5% of GA at t = 150 minutes. The vibrational modes obtained from FT-IR spectra confirmed the chemical composition of MIM-GA and its functionalization through of band at 770 cm-1. The contact angle measurements were 134.0±1.0° for electrospun MIM-GA and 125.0±1.2° for functionalized MIM-GA. The decrease was due to the absence of GA after the functionalization process. The produced MIM-GA by electrospinning acquired the recognition property of the GA imprinted polymer synthesized, which can be used for the specific detection, extraction, and purification of this important natural polyphenol. [ABSTRACT FROM AUTHOR]

By combining experimental and theoretical approaches, the electronic structure, molecular orientation, charge transfer dynamics and solar cell performance in donor/acceptor copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) films and blended with 6,6.-phenyl-C 61-butyric acid methyl ester (PSiF-DBT:PCBM) were investigated. Good agreement between experimental and theoretical PSiF-DBT UV-Vis absorption spectrum is observed and the main molecular orbitals contributing to the spectrum were determined using DFT single point calculations. Non-coplanar configuration was determined by geometric optimization calculation in isolated PSiF-DBT pentamer and corroborated by angular variation of the sulphur 1s near-edge X-ray absorption fine structure (NEXAFS) spectra. Edge-on and plane-on molecular orientations were obtained for thiophene and benzothiadiazole units, respectively. A power conversion efficiency up to 1.58%, open circuit voltage of 0.51 V, short circuit current of 8.71 mA/cm2 and a fill factor of 35% was obtained using blended PSiF-DBT:PCBM as active layer in a bulk heterojunction solar cell. Ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core-hole clock methodology around sulphur 1s absorption edge. Electron delocalization times for PSiF-DBT and PSiF-DBT:PCBM polymeric films were derived for selected excitation energies corresponding to the main transitions in the sulphur 1s NEXAFS spectra. The mixture of PSiF-DBT with PCBM improves the charge transfer process involving the π* molecular orbital of the thiophene units. [ABSTRACT FROM AUTHOR]

We present a high-resolution photoelectron spectroscopy investigation of condensed films of benzene, naphthalene, anthracene, tetracene, and pentacene. High spectroscopic resolution and a systematic variation of the molecular size allow a detailed analysis of the fine structures. The line shapes of the C 1s main lines are analyzed with respect to the different contributions of inhomogeneous broadening, vibronic coupling, and chemical shifts. The shake-up satellite spectra reveal trends, which give insight into the charge redistribution within the molecule upon photoexcitation. In particular, the shake-up between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) increases in intensity and moves closer toward the C 1s main line if the size of the aromatic system is increased. An explanation is given on the basis of the delocalization of the aromatic system and its capability in screening the photogenerated core hole. A comparison of the HOMO-LUMO shake-up position to the optical band gap gives additional insight into the reorganization of the electronic system upon photoexcitation. [ABSTRACT FROM AUTHOR]

The unoccupied molecular orbitals of metal-free phthalocyanine (H2PC), nickel-phthalocyanine (NiPC), and copper-phthalocyanine (CuPC) adsorbed on single crystal surfaces have been studied by inverse photoemission spectroscopy (IPES) and near-edge x-ray absorption spectroscopy (NEXAFS). The features observed in the experimental data are assigned by reference to molecular orbital calculations. Carbon and nitrogen 1s NEXAFS measurements of NiPC adsorbed on Cu(110) surface indicates that the phthalocyanine molecular planes are parallel to the surface. X-ray absorption data recorded at the Ni LIII and LII edges show that the unoccupied Ni 3d level is located in the plane of the phthalocyanine rings. [ABSTRACT FROM AUTHOR]

We have measured N 1s near edge absorption spectra and the kinetic energy distribution of electrons emitted in the decay of N 1s core-to-bound-state excitations in condensed pyridine, pyrazine, and s-triazine. The electron emission spectra generated in the electronic decay of the core to bound state resonances lead to singly charged, participator-type molecular final states, equivalent to the final states populated in photoemission, as well as to double hole (Auger) spectator-type final states screened by the presence of a π spectator electron. The deexcitation spectra, therefore, give insight into charge–transfer and screening processes in the initial core-electron excited state, as well as in the final spectator double-hole states. One of the most prominent participator features observed in the spectra of pyridine, pyrazine, and s-triazine is due to the emission of the most strongly bound π electrons, reflecting the dynamic screening of the core hole in the aromatic azabenzene molecules. The spectator states, on the other hand, exhibit a much reduced screening energy shift compared to linear molecules due to the delocalized nature of the π spectator electron. [ABSTRACT FROM AUTHOR]

The incidence of high-energy radiation onto icy surfaces constitutes an important route for leading new neutral or ionized molecular species back to the gas phase in interstellar and circumstellar environments, especially where thermal desorption is negligible. In order to simulate such processes, an acetonitrile ice (CH3CN) frozen at 120 K is bombarded by high energy electrons, and the desorbing positive ions are analyzed by time-of-flight mass spectrometry (TOF-MS). Several fragment and cluster ions were identified, including the Hn=1–3+, CHn=0–3+/NHn=0–1+; C2Hn=0–3+/CHn=0–3N+, C2Hn=0–6N+ ion series and the ion clusters (CH3CN)n=1–2+ and (CH3CN)n=1–2H+. The energy dependence on the positive ion desorption yield indicates that ion desorption is initiated by Coulomb explosion following Auger electronic decay. The results presented here suggest that non-thermal desorption processes, such as desorption induced by electronic transitions (DIET) may be responsible for delivering neutral and ionic fragments from simple nitrile-bearing ices to the gas-phase, contributing to the production of more complex molecules. The derived desorption yields per electron impact may contribute to chemical evolution models in different cold astrophysical objects, especially where the abundance of CH3CN is expected to be high. [ABSTRACT FROM AUTHOR]

Photon stimulated ion desorption and Auger decay spectra were measured for condensed thiophene around the S 1s-edge. Three kinds of ions, H+, S+, and S2+, were observed as main desorbed species. Partial ion yields (PIY) have been determined for these three fragment ions as a function of the photon energy. It was found that the indirect x-ray induced electron stimulated desorption mechanism plays an important role in H+ ion desorption. For S+ ion desorption, on the other hand, a pronounced enhancement at ∼3 eV away from the first core-to-valence resonance was observed in the PIY curve. On the basis of the results for the Auger decay spectra, the enhancement of S+ desorption at ∼3 eV away from the first resonance is interpreted in terms of the effective screening of positive holes due to the existence of Rydberg electrons. [ABSTRACT FROM AUTHOR]

Spectra reflecting the formation of single-site double-core-hole pre-edge states involving the N 1s and C 1s core levels of acetonitrile have been recorded by means of high-resolution single-channel photoelectron spectroscopy using hard X-ray excitation. The data are interpreted with the aid of ab initio quantum chemical calculations, which take into account the direct or conjugate nature of this type of electronic states. Furthermore, the photoelectron spectra of N 1s and C 1s singly core-ionized states have been measured. From these spectra, the chemical shift between the two C 1s -1 states is estimated. Finally, by utilizing C 1s single and double core-ionization potentials, initial and final state effects for the two inequivalent carbon atoms have been investigated.

DNA nucleotides are used as a molecular recognition system on electrodes modified to be applied in the detection of various diseases, but immobilization mechanisms, as well as, charge transfers are not satisfactorily described in the literature. An electrochemical and spectroscopic study was carried out to characterize the molecular groups involved in the direct immobilization of DNA structures on the surface of nanostructured TiO 2 with the aim of evaluating the influence of the geometrical aspects. X-ray photoelectron spectroscopy at O1s and P2p core levels indicate that immobilization of DNA samples occurs through covalent (POTi) bonds. X-ray absorption spectra at the Ti2p edge reinforce this conclusion. A new species at 138.5eV was reported from P2p XPS spectra analysis which plays an important role in DNA-TiO 2 immobilization. The POTi/OTi ratio showed that quantitatively the DNA immobilization mechanism is dependent on their geometry, becoming more efficient for plasmid ds-DNA structures than for PCR ds-DNA structures. The analysis of photoabsorption spectra at C1s edge revealed that the molecular groups that participate in the C1s→LUMO electronic transitions have different pathways in the charge transfer processes at the DNA-TiO 2 interface. Our results may contribute to additional studies of immobilization mechanisms understanding the influence of the geometry of different DNA molecules on nanostructured semiconductor and possible impact to the charge transfer processes with application in biosensors or aptamers., (Copyright © 2018 Elsevier B.V. All rights reserved.)