Spectra Of Mg Research Articles

Photodissociation of Mg+–XCH3 (X=F, Cl, Br, and I) complexes. I. Electronic spectra and dissociation pathways

Photodissociation spectra of Mg+-XCH3 (X=F, Cl, Br, and I) complexes have been measured in the ultraviolet region (225-415 nm). Several fragment ions with and without charge transfer (CT), Mg+, XCH3+, MgX+, MgCH3+, CH3+, and X+, were formed by evaporation (intermolecular bond dissociation) and intracluster reaction (intramolecular bond dissociation) via excited electronic states. Branching ratios of these ions were found to depend both on absorption bands and on halogen atoms. The ground states of the complexes were calculated to have geometries in which the Mg atom lies next to X atom of methyl halide molecules. Positive charges of the complexes are confirmed to be almost localized on Mg. Observed absorption bands were assigned to the transitions of the Mg+2P-2S atomic line perturbed by interactions with methyl halide molecules. Branching ratios of fragment ions can be partly explained by the stability of fragment ions and neutral counterparts. From the excited state potential energy curves along the Mg-X bond distance, dissociation reaction after CT was concluded to proceed predissociatively; potential curve crossings between the initially excited states and repulsive CT states may have a crucial role in the formation of CH3+, XCH3+, and X+. In particular, XCH3+ ions were formed via repulsive CT states having a character of electron excitation from Xnp to Mg+3s.

Surface states at close-packed surfaces of simple metals

Angle-resolved photoemission spectra from close-packed surfaces of thin epitaxial films of the earth-alkali metals Mg, Ca, and Sr on W(110) are reported. While normal emission spectra of Mg are dominated by huge emissions from a Shockley surface state, respective emissions are lacking for Ca and Sr. It is shown by means of LDA band-structure calculations that the band gap responsible for the surface state of Mg is Shockley inverted, while admixtures of $d$ states to the valence bands lead in case of Ca and Sr to the formation of ordinary gaps that are not suited for Shockley surface states. Consequences of this finding for the surface related electron structure of noble metals, Zn and Al group elements and rare-earth metals are discussed.

Study of A-site doping of SrBi4Ti4O15 Bi-layered compounds using micro-Raman spectroscopy

The temperature-dependent Raman spectra of Mg- and La-doped SrBi4Ti4O15 (SBT) were studied in the range 40–590 °C. A quantum chemistry calculation was employed to estimate these two substitution states. It was found that A-site doping in this study not only caused multiplicative substitution states, but also the Raman spectra changed with the substitution amount. In a La-doped perovskite-like layer, La would occupy the Bi site when x>0.10 and the 314 and 550 cm-1 modes related to the rotating and tilting of the TiO6 octahedron firstly became wide and then became sharp. With the increase of the substitution amount, both substitution states of Mg-doped SBT lead to the widening of 270 and 520 cm-1 peaks.

Structure of Mg2.56V1.12W0.88O8 and Vibrational Raman Spectra of Mg2.5VWO8 and Mg2.5VMoO8.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

An X-ray photoemission study of interfacial reaction during annealing of Mg/GaAs(100) interface

In this paper, we present an in situ annealing study on Mg(15 A)/GaAs(100) interface using X-ray photoelectron spectroscopy (XPS). The core level results indicate that an interfacial reaction starts between Mg and Ga atoms at room temperature and enhances with annealing. However, at a higher temperature of annealing, a mixed layer of ternary Mg–Ga–As phase is formed at the interface. Corresponding Auger spectra of Mg, Ga and As also show considerable modifications in their nature and therefore support the above reaction. The observed results are correlated and interpreted in terms of continuous changes in electronic and chemical environment at the Mg/GaAs interface. Copyright © 2005 John Wiley & Sons, Ltd.

Fine-Structure Spectra of Metal Complexes of Porphin in Tetrahydrofuran at Low Temperatures: Manifestation of Nonplanarity Effects

The fine-structure fluorescence spectra of Mg and Zn porphins in solid tetrahydrofuran matrices at the liquid helium temperature are recorded for the first time. The fluorescence spectra of Mg porphin molecules deposited from the gas phase on a sapphire substrate simultaneously with tetrahydrofuran molecules are measured. Based on the data obtained from the fluorescence and fluorescence excitation spectra, it is ascertained that there are two noninteracting spectrally different long-and short-wavelength forms of metal complexes of porphins in the ground state. In the case of Mg porphin, the spectral gap for these two forms at 4.2 K amounts to 330 cm−1. The short-wavelength form is attributed to the nonplanar saddle conformation of a porphin molecule, while the long-wavelength form is associated with the nonplanar domed conformation, in which the central metal ion is displaced out of the plane of the porphyrin ligand. The fine-structure fluorescence spectra of both forms of Mg and Zn porphins are measured in tetrahydrofuran at 4.2 K upon selective laser excitation. The frequencies of the normal vibrations in the ground electronic state are determined and the reasons for the differences in the vibrational frequencies of the forms are discussed.

Photodissociation and ab initio studies of Mg+(NH3)n, n=1–4: Electronic structure and photoinduced reaction

Photodissociation spectra of Mg+(NH3)n (n=1–4) cluster ions are examined in the wavelength region of 240–1200 nm. From the comparison with the results of ab initio calculations for the structure and the excitation energies of these clusters, the observed absorption bands are assigned to the transitions derived from the P2–2S transition of Mg+ ion. The extensive redshift of the observed spectra is ascribed to the formation of a one-center ion-pair state. In the photolysis of Mg+NH3, NH3+ and Mg+NH2 ions are produced via photoinduced charge transfer and intracluster reaction processes, respectively, in addition to the Mg+ ion generated by the evaporation of ammonia molecules. For n=2, both the intracluster reaction and evaporation are dominant decay processes, while the evaporation is the sole photodissociation channel for larger clusters. The branching fractions of these processes are found to depend strongly on the solvation number n and also on the photolysis wavelength. The energetics and the dynamics of the dissociation processes are discussed in relation to the redox reaction of metal ions.

X-RAY ABSORPTION STUDY OF Mg1-xAlxB2 AT B K-EDGE

We have measured B K-edge X-ray absorption spectra of Mg 1-x Al x B 2 (x=0.0 ~ 0.4) using bulk-sensitive total fluorescence yield (TFY) at room temperature and 30 K. In contrast to previous reports no peaks near 192 eV and 194 eV could be observed after repeated scraping, indicating their origin being due to surface contamination. These clean spectra show a peak right above the absorption threshold, anticipated from transition to the unoccupied B 2p states. Except in the intermediate Al doping range of x ~ 0.1 to 0.28 the threshold peak intensity decreases, consistent with pσ-hole filling. The increase of peak intensity in the intermediate range is correlated with structural phase transition.

Effect of the Al content on the optical phonon spectrum inMg1−xAlxB2

Raman and infrared absorption spectra of Mg(1-x)Al(x)B(2) have been collected for 0<x<0.5 in the spectral range of optical phonons. The x-dependence of the peak frequency, the width and the intensity of the observed Raman lines has been carefully analized. A peculiar x-dependence of the optical modes is pointed out for two different Al doping ranges. In particular the onset of the high-doping structural phase previously observed in diffraction measurements is marked by the appearence of new spectral components at high frequencies. A connection between the whole of our results and the observed suppression of superconductivity in the high doping region is established.

Infrared and Raman studies of the solids in the Mg(CH 3COO) 2–Zn(CH 3COO) 2–H 2O system

The infrared and Raman spectra of Mg(CH 3COO) 2·4H 2O, Zn(CH 3COO) 2·2H 2O and the double salt MgZn(CH 3COO) 4·4H 2O have been recorded and discussed with respect to the internal modes of the acetate ions and the water molecules. MgZn(CH 3COO) 4·4H 2O crystallizes in the triclinic system with lattice parameters: a=10.441(3) A ̊ , b=10.353(3) A ̊ , c=8.949(3) A ̊ , α=105.67(2)°, β=114.77(2)°, γ=77.52(2)°, V=839.8(3) A ̊ 3. The analysis of the spectra of MgZn(CH 3COO) 4·4H 2O reveals the existence of probably at least three crystallographically non-equivalent acetate ions in the lattice. The strength of the hydrogen bonds in the three salts is studied by the method of IR matrix spectroscopy (matrix-isolated HDO molecules). The frequencies of the OD modes reveal that the acetate oxygens are stronger hydrogen bond acceptors than the water oxygens and the non-coordinated acetate oxygens show stronger acceptor abilities as compared to that of the coordinated ones. Comparatively strong hydrogen bonds are formed in Zn(CH 3COO) 2·2H 2O. The number of the bands corresponding to the uncoupled OD vibrations in MgZn(CH 3COO) 4·4H 2O evidences that at least four crystallographically different water molecules are expected to exist in the lattice. The water librations in the salts under study are also discussed.

Photodissociation studies of microsolvated metal cation complexes Mg+(NCCH3)n (n=1–4)

Acetonitrile-solvated Mg+ complexes Mg+(NCCH3)n were produced in a pick-up source. The Mg+(NCCH3)n clusters were subjected to photodissociation in a time-of-flight reflectron mass spectrometer. Except for a minor reactive product Mg+-NC at short wavelengths, only nonreactive (or evaporation) fragments were observed from photodissociation of Mg+(NCCH3)n (n=1–4). Action spectra of Mg+(NCCH3)n (n=1–4) were recorded in the spectral region of 230–560 nm, which provide insight into the structure and photodissociation dynamics of the complexes. For all the complexes we studied, the ligands are believed to be in the first solvation shell. Both the evaporation and reaction processes occur on the ground state surfaces of the complexes. By using the DFT/B3LYP and CIS methods, the most stable ground-state structures and the excitation spectra for Mg+(NCCH3)1–3 were obtained. The ab initio predictions appear to be consistent with the experimental results.

Electronic structure and luminescence properties of magnesium fluoroborates doped with Ce 3+ ions

The luminescence properties of Ce 3+ ions in magnesium fluoroborates, Mg 3BO 3F 3 and Mg 2BO 3F, upon X-ray and synchrotron radiation excitation are reported and discussed. VUV excitation spectra of Mg 3 BO 3 F 3 : Ce 3+ can be reasonably explained by taking into account several factors, such as the electronic structure of Mg 3BO 3F 3 and energy loss mechanisms. It is suggested that the luminescence behavior of Ce 3+ is influenced by the presence of F − vacancies in the lattice.

Room temperature UV emission of Mg xZn 1− xO films

II–VI wide band-gap semiconductor ternary Mg x Zn 1− x O nanocrystalline films have been successfully formed on conductive glass from ZnO powder by electrophoresis deposition (EDP). In comparison with ZnO powder, the Mg x Zn 1− x O films presented a more preferential crystalline orientation. Room temperature (RT) PL spectra of Mg x Zn 1− x O films revealed a stronger band-edge ultraviolet (UV) emission and a narrower FWMH of 13 nm than that of ZnO powder. The UV emission peak of Mg x Zn 1− x O film is located at the range of 375–381 nm with a small blue shift from that of ZnO powder. In addition, the ratio of PL peak intensity of band-edge emission to the deep-level emission in Mg x Zn 1− x O films reached as high as 135:1 while compared with 23:1 of ZnO powder under the same He–Cd laser excitation level. Consequently, these electrophoretic deposition (EPD) Mg x Zn 1− x O films exhibited a good quality for excitonic emission at RT.

Spectroscopy and reactivity of size-selected Mg+–methanol clusters

This work presents photodissociation spectra of Mg+(CH3OD)n (n=1–5). Mass spectrometry of the parent cluster ions shows that C–H bond cleavage occurs in the ground electronic state. The branching ratios for products of photodissociation show strong selectivity; methyl loss is the exclusive quenching channel in n=1, while a unique pathway that eliminates CH3D occurs in n=2. Methyl loss does not occur for clusters with more than three solvent molecules. The maximum of spectral intensity shifts to the red with increasing cluster size until halting at n=3. These data signal the formation of a solvent shell at a relatively small size. As the cluster size increases, ligand loss and D atom loss become overwhelmingly favored. We address the selectivity in the products in terms of the initial photoexcited state, nonadiabatic coupling to the ground state potential energy surface, and subsequent dissociation and product formation dictated by dynamics on the ground state surface.

IR study of solid phases formed in the Mg(HCOO)2–Cu(HCOO)2–H2O system

The infrared (IR) spectra of Mg(HCOO)2·2H2O and Mg1−xCux(HCOO)2·2H2O mixed crystals (0<x≤0.5) have been recorded and the internal modes of the formate groups and the water molecules are reported. The number of the bands corresponding to the fundamental vibrations of the HCOO groups and the H2O molecules in the Mg(HCOO)2·2H2O spectrum reflects the existence of two crystallographically different formate groups and water molecules in coincidence with the structural data. The red-shift of the OD vibrations (matrix-isolated HDO molecules) at liquid nitrogen temperature as compared to ambient temperature (dv/dT>0) evidences for the formation of linear hydrogen bonds. The IR spectra of Mg1−xCux(HCOO)2·2H2O mixed crystals show that the regions of 3200–3400cm−1 (νOH), 2300–2500cm−1 (νOD of matrix-isolated HDO), 500–950cm−1 (water librations) are mostly sensitive to the coordination environment of the metal ions. So the analysis of the IR spectra reveals that the copper ions are localized predominatingly at Me(1) sites in the mixed crystals, i.e. at sites with a six-fold coordination through six oxygen atoms from the formate groups only. Mg0.26Cu0.74(HCOO)2·2H2O (new crystal phase) forms monoclinic crystals with lattice parameters: a=12.347(4); b=7.240(4); c=8.736(6)Åβ=103.08(5)°; SG P21/c. The internal modes of the formate groups and the water molecules in the new crystal phase are discussed by analogy to Mg(HCOO)2·2H2O and Cu(HCOO)2·2H2O, since the structutal data are not available. The analysis of the spectra in the region of the uncoupled OD vibrations shows that probably more than two water molecules are expected to exist in the structure. It is assumed that the water molecules bonded to the copper ions form stronger hydrogen bonds due to the stronger Cu–H2O interactions (synergetic effect) than those bonded to the magnesium ions. The librational modes of the water molecules in all the solid phases studied are also discussed.

The role of the Mg 2+ cation in ATPsynthase studied by electron paramagnetic resonance using VO 2+ and Mn 2+ paramagnetic probes

The electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectra of Mg 2+-depleted chloroplast F1-ATPase substituted with stoichiometric VO 2+ are reported. The ESEEM and HYSCORE spectra of the complex are dominated by the hyperfine and quadrupole interactions between the VO 2+ paramagnet and two different nitrogen ligands with isotropic hyperfine couplings | A 1|=4.11 MHz and | A 2|=6.46 MHz and nuclear quadrupole couplings e 2q Q 1≈3.89–4.49 MHz and e 2q Q 2≈1.91–2.20 MHz, respectively. Aminoacid functional groups compatible with these magnetic couplings include a histidine imidazole, the ε-NH 2 of a lysine residue, and the guanidinium group of an arginine. Consistent with this interpretation, very characteristic correlations are detected in the HYSCORE spectra between the 14N Δ M I=2 transitions in the negative quadrant, and also between some of the Δ M I=1 transitions in the positive quadrant. The interaction of the substrate and product ADP and ATP nucleotides with the enzyme has been studied in protein complexes where Mg 2+ is substituted for Mn 2+. Stoichiometric complexes of Mn·ADP and Mn·ATP with the whole enzyme show distinct and specific hyperfine couplings with the 31P atoms of the bonding phosphates in the HYSCORE (ADP, A( 31P β)=5.20 MHz; ATP, A( 31P β)=4.60 MHz and A( 31P γ)=5.90 MHz) demonstrating the role of the enzyme active site in positioning the di- or triphosphate chain of the nucleotide for efficient catalysis. When the complexes are formed with the isolated α or β subunits of the enzyme, the HYSCORE spectra are substantially modified, suggesting that in these cases the nucleotide binding site is only partially structured.

Photophysics of metal atoms in rare-gas complexes, clusters and matrices

Experimental studies of electronic spectra and dynamics of metal atoms M of groups I, II and III of the periodic system interacting with rare-gas atoms G in 1:1 MG complexes, MGn clusters and M/G centres in matrices are reviewed. It is shown that the necess n ary condition for a good understanding of the properties of M/G solids is a detailed knowledge of the M-G interactions in diatomic MG molecules. In spite of their apparent simplicity, the electronic spectra of MG and M/G systems are complex because of a drastic difference between the M-G potentials in ground and excited states of M atoms.

The doping of GaN with Mg diffusion

The characteristics of GaN films diffused with Mg were studied. The undoped GaN films were grown by metalorganic chemical vapor deposition (MOCVD). The photoluminescence (PL) spectra of Mg diffused GaN showed a broad violet emission. The Mg-diffused GaN was p-type conductivity with a mobility of 13 cm 2/V-s and a hole concentration of 3×10 15/cm 3 at a diffusion temperature of 1100°C. However, the samples, which were diffused at 1100°C, showed a red emission peak after the annealing process. From the diffusion depth profile observed by secondary ion mass spectrometry (SIMS), we obtained the activation energy of 1.3 eV for Mg diffusion in GaN.

Ultraviolet spectra of Mg in liquid helium

Emission and absorption spectra of Mg atoms implanted in liquid helium have been observed in the ultraviolet region. We have presented a model of exciplex formation of Mg-He10 and found that this model is more suitable for understanding the dynamics in the \(\) transition than the bubble model.

Ultraviolet spectra of Mg in liquid helium

Ultraviolet spectra of Mg in liquid helium