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1.
Michael P. Schwartz 《Surface science》2007,601(4):945-953
The adsorption of acetonitrile on the Si(0 0 1) surface has been investigated using X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). XPS and FTIR spectra indicate that adsorbed acetonitrile forms two correlated binding configurations, a CN species with a strong FTIR absorption at 1540 cm−1 and a CCN (ketenimine) species that has a very strong FTIR absorption at 1952 cm−1. The CCN FTIR peak at 1952 cm−1 shows a striking polarization dependence, with the infrared transition dipole almost entirely in the plane of the sample and parallel to the SiSi dimer axis. Our data suggests that the primary CCN structure results from cleavage of two C-H bonds, forming a structure in which the N and terminal C atom are both linked to the surface. Temperature-dependent experiments help to elucidate the complicated reaction mechanism for acetonitrile adsorbing onto the Si(0 0 1) surface. Dosing at higher temperature increases the amount of CCN relative to CN species while heating leads to direct transformation of the CN to the CCN species. Our results indicate that previous studies, which considered only products formed by cleavage of a single C-H bond, have misidentified the primary ketenimine product. A reinterpretation of the earlier results, combined with data presented here, sheds new light onto the products and mechanism of interaction of acetonitrile with Si(0 0 1). 相似文献
2.
Chemisorption of 1,1-dichloroethene (Cl2CCH2) to a Si(1 1 1)-7 × 7 surface was studied by means of X-ray photoelectron spectroscopy using synchrotron radiation, recording chlorine 2p and carbon 1s spectra. For carbon 1s, spectral assignment of the chemisorbed species is based on quantum chemical calculations of chemical shifts in model compounds.The results confirm the identity of covalently bonded 1-chlorovinyl (-CClCH2) and vinylidene (CCH2) adspecies. Upon chemisorption at room temperature it was found that about one-third of the molecules break one C-Cl bond while about two-thirds of the adsorbates break two C-Cl bonds. We do not, however, find evidence for isomerization of CCH2 to di-bonded vinylene (-CHCH-). 相似文献
3.
High-resolution Fourier transform infrared spectra of natural trans-ClHCCHF and of its isotopologue trans-ClHCCDF have been recorded in the region between 700 and 1150 cm−1 with the purpose to analyze the ν11 fundamental of the main species and the ν10 of its deuterated compound. Both bands, of symmetry species A″, present c-type envelope absorptions. Beside the expected features, the K structure of the P(J), Q(J), and R(J) manifolds was resolved and identified; the assignment of the rovibrational transitions was extended up to J = 92 and Ka = 13 for the trans-35ClHCCHF and up to J = 86 and Ka = 10 for trans-35ClHCCDF. More than 2900 and 2700 lines for the main and deuterated species, respectively, were analyzed by a least-squares procedure and reliable spectroscopic molecular parameters were determined for both isotopologues. 相似文献
4.
Hai Hua Tang 《Surface science》2007,601(16):3293-3302
The interaction of ethyl vinyl ketone (EVK) with Si(1 1 1)-7 × 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The disappearance of both stretching vibrations of CH2 (3099 cm−1) and CO (1684 cm−1) coupled with the appearance of new CC stretching mode (1660 cm−1) in the HREELS spectra of chemisorbed EVK clearly demonstrates the direct involvement of conjugated CC and CO bonds to form a SiC1H2C2HC3(C4H2C5H3)OSi surface species via [4 + 2]-like cycloaddition in a highly selective manner. In addition, XPS studies show that the C1s binding energies of C1/C2 and C3 upon chemisorption display chemical downshifts of 0.8 eV and 2.2 eV, respectively, further confirming the proposed [4 + 2]-like cycloaddition reaction for the EVK/Si(1 1 1)-7 × 7 system. DFT theoretical calculations suggest that the proposed [4 + 2]-like cycloadduct is thermodynamically most favorable. 相似文献
5.
The quadratic, cubic and semi-diagonal quartic force field of nitric acid has been calculated at the CCSD(T) level of theory employing a basis set of triple-ζ quality. A semi-experimental equilibrium structure has been derived from experimental ground state rotational constants and rovibrational interaction parameters calculated from the ab initio force field. It is found that the A and B semi-experimental equilibrium rotational constants of the 18O isotopologues (for which the rotation of principal axes is large) cannot be accurately reproduced. This problem is discussed and a remedy is proposed. Finally, the semi-experimental structure is in agreement with the ab initio structure calculated at the CCSD(T) level of theory using a basis set of at least quadruple-ζ quality and a core correlation correction, except for the long NO single bond for which the CCSD(T) value is too short due to inadequate treatment of electron correlation. The empirical structures are also determined and their accuracy is discussed. The best equilibrium structure is: re(NOsyn) = 1.209(1) Å, re(NOanti) = 1.194(1) Å, re(NO) = 1.397(1) Å, re(OH) = 0.968(1) Å, ∠(ONOsyn) = 115.8(1)°, ∠(ONOanti) = 114.2(1)° and ∠(NOH) = 102.2(1)°. 相似文献
6.
G.S. Grubbs II A. King W.C. Bailey S.A. Cooke 《Journal of Molecular Spectroscopy》2010,263(2):127-134
A potential energy scan of chlorodifluoroacetyl chloride, CF2ClC(O)Cl, at the MP2/6-311+G(d) level of theory predicts stable gauche and trans conformers, with Egauche<Etrans. Ab initio calculations were made of approximate equilibrium structures of these and, on these structures, calculations were made of 35Cl and 37Cl nuclear quadrupole coupling constant tensors. Coupling constants here predicted, as well as rotational constants and molecular dipole moments, are applied to aid analyses of experimental microwave spectra. Chirped pulse Fourier transform microwave spectroscopy has been used to rapidly record the rotational spectra of four isotopologues of the title molecule, CClF2C(O)Cl, namely 35Cl35Cl, 35Cl37Cl, 37Cl35Cl, and 37Cl37Cl. Only the gauche conformer was observed under the experimental conditions. For the four isotopologues a total of 464, 219, 197, and 77 transitions have been recorded, respectively. With the exception of the 37Cl37Cl isotopologue sufficient data was available to determine all Cl quadrupole coupling tensors. Comparisons between the theoretical and experimental results are made. 相似文献
7.
Maryam Ebrahimi 《Surface science》2009,603(9):1203-5808
Competition between the CC functional group with the OH group in allyl alcohol and with the CO group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2×1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] CO cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] CC cycloaddition products. Temperature-dependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2×1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] CC cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2×1 surface in selective reactions of the Si dimers with the O−H group in allyl alcohol and with the CO group in allyl aldehyde over the CC functional group common to both molecules. 相似文献
8.
9.
N. Mireault 《Applied Surface Science》2008,254(21):6908-6914
Plasma source ion implantation (PSII), a hybrid implantation technique between ion beams and immersion plasmas has been used to modify CR39 surfaces for improved wettability providing both advancing (θa) and receding (θr) contact angles below 5°. The modifications brought to the polymer surface structure have been characterized by X-ray photoelectron spectroscopy (XPS) and its combination with chemical derivatization (CD-XPS). Oxygen desorption has been observed in spite of the very hydrophilic surfaces. C1s XPS peak has been displaced toward greater energies, while the opposite has been found for O1s, both involving new components and strong modifications after ion implantation treatment. Strong evidences about the formation of new chemical functions, like OOH, COOH and CC, have been found and have provided an explanation for the increased wettability. 相似文献
10.
An electronic structural study of the ground electronic states for the chemically similar bicyclic norbornadiene (NBD, C7H8, X1A1), norbornene (NBN, C7H10, X1A′) and norbornane (NBA, C7H12, X1A1) molecules is provided quantum mechanically. Initially, the unique orbital imaging capability of electron momentum spectroscopy is used to validate which of the quantum mechanical models available to us for these calculations best represents these species. Thereafter, individual molecular point group symmetry is incorporated in the calculations with energy minimization in the search for equilibrium geometries of the species using MP2/TZVP and B3LYP/TZVP models. The optimized geometries compare favourably with available crystallographic results and also build confidence in cases where the crystallographic results are ambiguous. The present study aims to reveal the particular subtle structural deviation of the species, which results in significant molecular property differences among these organic compounds. This work intends to probe bonding information of the species and the impact, on the seven member carbon skeleton, as the CC double bonds of NBD are progressively saturated by hydrogen atoms to give NBN and NBA. Significant changes observed through the present work include: (i) the seven member carbon skeleton tends to relax the strain whenever possible and (ii) the ethano ring experiences greater structural changes than the methano bridge. The methano bridge (C(1)-C(7)-C(4)) of the less symmetric NBN molecule (Cs) tilts to the single C-C bond side of the ethano ring of the molecule (rather than the CC side), producing a dihedral angle of 8.7° between plane H-C(1)-C(4) (the yz-plane) and plane C(1)-C(7)-C(4). Our work suggests that it is this unique dihedral angle in NBN which causes the molecules exo-reactivity and is also responsible for the extra activity of its CC bond. 相似文献
11.
Layers prepared by pulsed TEA CO2 pulsed laser ablation (PLA) of SiO and SiO2 targets in helium were exposed to hydrogen and deuterium atmosphere up to several kPa. The deposited layers were investigated by FTIR, EPR and XP spectroscopy. Among various Si species silyl radical Si(·)H (Si(·)D) at 2166 (1568) cm−1—H(I) center—and silyl hydroperoxide SiOOH (SiOOD) at 3587 (2648) cm−1 were identified in FTIR spectra. Chemical pathways for production of these species are discussed. Experimental results are supported by quantum chemical calculations. 相似文献
12.
X-ray photoelectron spectroscopy (XPS) was used to characterise the effects of low energy (<2 eV) argon ion plasma surface modification of TiO2 thin films deposited by radio frequency (RF) magnetron sputter system. The low energy argon ion plasma surface modification of TiO2 in a two-stage hybrid system had increased the proportion of surface states of TiO2 as Ti3+. The proportion of carbon atoms as alcohol/ether (COX) was decreased with increase the RF power and carbon atoms as carbonyl (CO) functionality had increased for low RF power treatment. The proportion of C(O)OX functionality at the surface was decreased at low power and further increase in power has showed an increase in its relive proportion at the surface. The growth of S180 cells was observed and it seems that cells are uniformly spreads on tissue culture polystyrene surface and untreated TiO2 surfaces whereas small-localised cell free area can be seen on plasma treated TiO2 surfaces which may be due to decrease in C(O)OX, increase in CO and active sites at the surface. A relatively large variation in the surface functionalities with no change in the surface roughness was achieved by different RF plasma treatments of TiO2 surface whereas no significant change in S180 cell growth with different plasma treatments. This may be because cell growth on TiO2 was mainly influenced by nano-surface characteristics of oxide films rather than surface chemistry. 相似文献
13.
NEXAFS data [S. Rangan et al., Phys. Rev. B 71 (2005) 165319] and FTIR data [M.P. Schwartz, R.J. Hamers, Surf. Sci. 601 (2007) 945] apparently do not converge in the identification of the reaction products of acetonitrile (CH3CN) with Si(0 0 1)-2 × 1 at room temperature. Using DFT calculations of core-excited/core-ionized spectra and of IR vibrational frequencies and intensities, we show the consistency of the body of experimental data. Three species are present on the surface in equivalent amounts, a CN moiety, a pendent CN and a CCN ketenimine submitted to a strong twist imposed by the Si bond directionality. More generally, the paper shows the usefulness of spectroscopic data simulations in the elucidation of complex surface chemistry problems. 相似文献
14.
Improvement and mechanism of interfacial adhesion in PBO fiber/bismaleimide composite by oxygen plasma treatment 总被引:2,自引:0,他引:2
The improved interfacial adhesion of PBO fiber-reinforced bismaleimide composite by oxygen plasma processing was investigated in this paper. After treatment, the maximum value of interlaminar shear strength was 57.5 MPa, with an increase of 28.9%. The oxygen concentration of the fiber surface increased, as did the surface roughness, resulting in improvement of the surface wettability. The cleavage and rearrangement of surface bonds created new functional groups OCO, NCO and NO, thereby activating the fiber surface. And long-time treatment increased the reaction degree of surface groups while destroyed the newly-created physical structures. The enhancement of adhesion relied primarily on the strengthening of chemical bonding and mechanical interlocking between the fiber and the matrix. The composite rupture planes indicated that the fracture failure shifted from the interface to the matrix or the fiber. 相似文献
15.
16.
Metal antibacterial reagents are effective in the enhancement of the antimicrobial properties of medical polymers. However, incorporation of metal antibacterial reagents into polymers using conventional methods usually results in unstable antimicrobial effects. Our previous research demonstrates that plasma immersion ion implantation (PIII) can be used to effectively incorporate metal antibacterial reagents such as Cu into polyethylene (PE) in the near surface region up to several hundred nanometers without causing noticeable damage to the polymer matrix. In this work, various gases including NH3, O2, and N2 were plasma-implanted in concert with Cu plasma immersion ion implantation to study the effects of these gas species on the release rate of Cu from the substrate. Our experimental results reveal that the copper depth profiles are not affected significantly by NH3, O2, or N2 co-implantation and these gas elements have similar depth profiles as Cu. Chemical analyses demonstrate that polar functional CO, CO, CN, CN, and CN bonds formed in the substrate play an important role in regulating Cu out-diffusion. Among the three gas species, N2 shows the best effects in regulating Cu out-diffusion and produces the best long term antibacterial properties. The Cu retention and out-diffusion mechanism in the ion-implanted polyethylene is described. 相似文献
17.
Acetonitrile (CH3CN) adsorbs on Si(0 0 1)-2 × 1 at room temperature under two forms, a cycloaddition-like adduct (Si-CN-Si) and a pendent cyano (Si-CH2-CN) resulting from the decomposition of the molecule. Resonant Auger spectroscopy has been used to study the excited-state-dependent electron transfer from the N 1s core-excited molecular adsorbate to the silicon substrate, using the core-hole lifetime (∼6 fs) as an internal clock. It is shown that the πCN∗ NEXAFS state lies within the silicon bandgap because of a core-excitonic effect. Therefore no charge transfer of the excited electron to the substrate is observed. On the other hand the πCN∗ NEXAFS state is placed within the silicon conduction band. Excitation to this orbital leads to valence/Auger spectra in which both resonant and normal Auger contributions are observed. Therefore there is evidence for a charge transfer from the pendent CN to the silicon surface, on a timescale estimated to tens of femtoseconds. 相似文献
18.
Philipp Martin Schmidt Karsten Horn J. Hugo Dil Thorsten U. Kampen 《Surface science》2007,601(8):1775-1780
Stilbene (1,2-diphenylethylene) has shown an intriguing isomerisation behavior and may serve as a model system for “molecular switches” incorporating a CC double bond. To evaluate the possible use of such molecules as molecular switches on semiconductor surfaces, the adsorption of cis- and trans-stilbene on Si(1 0 0) has been investigated. Identification of both isomers is achieved by differences in adsorption geometry as revealed by NEXAFS, and differences in electronic structure in the occupied and unoccupied molecular orbitals. For both isomers, bonding takes place via the CC double bond to the Si dimer atoms allowing for free movement of the aromatic rings, a necessary prerequisite for photoinduced isomerisation on the surface. Our experimental results agree well with theoretical calculations. 相似文献
19.
Bianca Montanari Sidney J.L. Ribeiro Gaël Poirier Máximo S. Li 《Applied Surface Science》2008,254(17):5552-5556
Thin films were prepared using glass precursors obtained in the ternary system NaPO3BaF2WO3 and the binary system NaPO3WO3 with high concentrations of WO3 (above 40% molar). Vitreous samples have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. Several structural characterizations were performed by Raman spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES) at the tungsten LI and LIII absorption edges. XANES investigations showed that tungsten atoms are only sixfold coordinated (octahedral WO6) and that these films are free of tungstate tetrahedral units (WO4). In addition, Raman spectroscopy allowed identifying a break in the linear phosphate chains as the amount of WO3 increases and the formation of POW bonds in the films network indicating the intermediary behavior of WO6 octahedra in the film network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed identifying the presence of WO− and WO terminal bonds and a progressive apparition of WOW bridging bonds for the most WO3 concentrated samples (above 40% molar) attributed to the formation of WO6 clusters. 相似文献
20.
An accelerated quantum chemical molecular dynamical code “Colors-Excite” was used to investigate the photolysis of alkyl nitrites series, RONO (RCH3 and C(CH3)3) on copper surfaces. Our calculations showed that the photo-dissociated processes are associated with the alkyl substituents of RONO when adsorbed on copper surfaces. For RCH3, a two-step photolysis reaction occurred, yielding diverse intermediate products including RO radical, NO, and HNO, consistent with those reported in gas phase. While for RC(CH3)3, only one-step photolysis reaction occurred and gave intermediate products of RO radical and NO. Consequently, pure RO species were achieved to adsorb on metal surfaces by removing the NO species in photolysis reaction. The detailed photo-dissociated behaviors of RONO on copper surfaces with different alkyl substituents which are uncovered by the present simulation can be extended to explain the diverse dissociative mechanism experimentally observed. The quantum chemical molecular dynamical code “Colors-Excite” is proved to be highly applicable to the photo-dissociations on metal surfaces. 相似文献