E2 Band Research Articles

Electric-quadrupole and magnetic-dipole contributions to the ν2+ν3 band of carbon dioxide near 3.3 µm

The recent detections of electric-quadrupole (E2) transitions in water vapor and magnetic-dipole (M1) transitions in carbon dioxide have opened a new field in molecular spectroscopy. While in their present status, the spectroscopic databases provide only electric-dipole (E1) transitions for polyatomic molecules (H2O, CO2, N2O, CH4, O3…), the possible impact of weak E2 and M1 bands to the modeling of the Earth and planetary atmospheres has to be addressed. This is especially important in the case of carbon dioxide for which E2 and M1 bands may be located in spectral windows of weak E1 absorption. In the present work, a high sensitivity absorption spectrum of CO2 is recorded by Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OFCEAS) in the 3.3 µm transparency window of carbon dioxide. The studied spectral interval corresponds to the region where M1 transitions of the ν2+ν3 band of carbon dioxide were recently identified in the spectrum of the Martian atmosphere. Here, both M1 and E2 transitions of the ν2+ν3 band are detected by OFCEAS. Using recent ab initio calculations of the E2 spectrum of 12C16O2, intensity measurements of five M1 lines and three E2 lines allow us to disentangle the M1 and E2 contributions. Indeed, E2 intensity values (on the order of a few 10–29 cm/molecule) are found in reasonable agreement with ab initio calculations while the intensity of the M1 lines (including an E2 contribution) agree very well with recent very long path measurements by Fourier Transform spectroscopy. We thus conclude that both E2 and M1 transitions should be systematically incorporated in the CO2 line list provided by spectroscopic databases.

Electronic and vibrational structure in the S0 and S1 states of corannulene.

Corannulene is a nonplanar aromatic hydrocarbon also known as a buckybowl. Its electronic and vibrational structure has been investigated by analyzing its fluorescence excitation spectrum and dispersed fluorescence spectrum in a supersonic jet. Its spectral features are in keeping with the expectation, confirmed by some previous results, that it has fivefold or C5v symmetry. The observed prominent vibronic bands in the S1 ← S0 transition have been assigned to e1 and e2 bands on the basis of theoretical calculations so that the S1 state was assigned to 1E2. The symmetry adapted cluster configuration interaction calculation supports this assignment of the S1 electronic state, although the time-dependent density functional theory calculation suggests that the S1 state is 1A2. It has also been shown that the normal coordinates for strong vibronic bands mainly include out-of-plane vibrational motion. The rotational envelopes are well explained by taking account of the Coriolis interaction between the degenerate vibrational and rotational levels. The mechanism of bowl-to-bowl inversion is also discussed with the results of theoretical calculations regarding the barrier to inversion and metastable conformation.

On the stress relaxation mechanism of GaN thin films grown on Si(111) substrates

Gallium nitride (GaN) thin films grown on Si(111) substrates via plasma-assisted molecular beam epitaxy were investigated. The morphology of GaN films was studied by scanning electron microscopy. It was found that GaN films at nanoscale contain a large amount of cavities. The Raman measurements of GaN/Si(111) system were performed and showed that the position of the GaN E2 (TO) band is close to that of unstrained GaN. We proposed a stress relaxation mechanism to explain the low stress state of GaN films.

Optical Transitions in ZnSe and CdTe Crystals with Involvement of the Cation d Bands

The permittivity spectra e1(E) and e2(E) of ZnSe and CdTe crystals are calculated in the range of 10–25 eV using their experimental reflectance spectra and Kramers–Kronig integral relations. The spectra are decomposed into thirteen and twelve separate transition bands for ZnSe and CdTe, respectively, using the improved nonparametric combined Argand diagram technique. The main spectral parameters, including the maximum energies and halfwidths and oscillator strengths, are determined. The oscillator strengths are found to be within 0.1–1.4 for ZnSe and 0.2–0.7 for CdTe. The obtained e2(E) bands are due to interband and exciton transitions with the involvement of cation core d bands of both crystals under consideration.

Coloration of molybdenum oxide thin films synthesized by spray pyrolysis technique

Photochromiccoatings of molybdenum oxide films were deposited on glass substrates by spray pyrolysis technique. The samples were prepared at two substrate temperatures of 250°C and 400°C using spray time varying between 1 and 5 min while the other spray operating parameters are fixed at their optimum values. The crystalline nature and crystallite size of the films were investigated by grazing angle X-ray diffraction. The surface topography was characterized by atomic force microscopy roughness data and particle size histograms. The X-ray diffraction patterns prove that the films deposited at substrate temperature of 250 °C and different spray time are amorphous while the films deposited at 400°C and different spray time are crystalline with only α-phase. The particle size distribution for the prepared samples are found to be in the range from 70 to 100nm. The particle size distribution tends to be narrow as the spray time increases which indicates the improvement in homogeneity of the samples. The optical absorption spectra of selected colorless samples before and after UV light irradiation was recorded. Two distinct absorption bands were observed: a sharp one related to the energy gap and a broader one at lower energy of 1.03eV to which the blue color of the sample after UV irradiation is related. This latter band is fitted with three sub-bands E1, E2 and E4 using a Lorentzian model. The intensity and position of these sub-bands depended on UV light exposure time. The sub-bands E1 and E4 are related to the bulk and surface paramagnetic color centers while the E2 band is related to pairing diamagnetic color centers.

Synthesis of ZnO aerogels nanopowders in supercritical methanol: effect of sol concentration on structural, morphological and optical properties

Nanocrystallines zinc oxide (ZnO) aerogels with different zinc acetate concentrations (0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 mol/L) have been synthesized in supercritical methanol. The as-obtained products were analyzed without any additional heat or chemical treatments. The XRD study reveals that all the prepared nanopowders have good polycrystalline hexagonal wurtzite structure with the high crystalline quality obtained for aerogel prepared with a 0.20 M sol concentration. The lattice parameters are not dependent on the precursor concentration. The particle size has found to be related to the sol concentration. SEM micrographs have shown that the agglomeration state of the as-prepared ZnO nanoparticles is significantly affected by the sol concentration. FTIR measurements have indicated the displacement of the Zn–O vibration band to the higher wave numbers with increasing sol concentration. Raman results have confirmed that E2 bands intensity depends on precursor concentration. TGA measurements show that the aerogels contain only small quantities of volatiles. The optical absorption and room temperature photoluminescence emission are not affected considerably by Zn2+ concentration.

Surface modifications caused by a swift heavy ion irradiation on crystalline p-type gallium antimonide

Surface modifications caused by a swift heavy ion irradiation on crystalline p-type gallium antimonide crystal have been reported. Single crystal, 100〉 orientations and ∼500μm thick p-type GaSb samples with carrier concentration of 3.30×1017cm−3 were irradiated at 100MeV Fe7+ ions. We have used 15UD Pelletron facilities at IUAC with varying fluences of 5×1010–1×1014 ions cm−2. The effects of irradiation on these samples have been investigated using, spectroscopic ellipsometry, atomic force microscopy and ultraviolet–visible–NIR spectroscopy techniques. Ellipsometry parameters, psi (Ψ) and delta (Δ) for the unirradiated sample and samples irradiated with different fluences were recorded. The data were fit to a three phase model to determine the refractive index and extinction coefficient. The refractive index and extinction coefficient for various fluences in ultraviolet, visible, and infrared, regimes were evaluated. Atomic force microscopy has been used to study these surface modifications. In order to have more statistical information about the surface, we have plotted the height structure histogram for all the samples. For unirradiated sample, we observed the Gaussian fitting. This result indicates the more ordered height structure symmetry. Whereas for the sample irradiated with the fluence of 1×1013, 5×1013 and 1×1014 ions cm−2, we observed the scattered data. The width of the histogram for samples irradiated up to the fluence of 1×1013 ion cm−2 was found to be almost same however it decreased at higher fluence. UV reflectance spectra of the sample irradiated with increasing fluences exhibit three peaks at 292, 500 and 617nm represent the high energy GaSb; E1, E1+Δ and E2 band gaps in all irradiated samples.

Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films

Origin of the Raman mode in nanocrystalline zinc oxide in the vicinity of A1 (LO) phonon mode induced by energetic heavy ions is reported. The evolution of this mode in the irradiated films is ascribed to the effect of disorder and the high density of lattice defects induced by irradiation. The presence of such defects is confirmed by the reduction in the intensity of E2 (high) mode and band bending of the near band edge absorption. A softening of the evolved Raman mode with increasing in ion fluence is also observed. This softening cannot be attributed to spatial confinement of phonons, as the sizes of the crystallites are large. Therefore, it is explained in terms of the combined effects of phonon localization by lattice defects and the structural strain in the lattice induced by electronic energy loss transferred by energetic heavy ions.

Synthesis and characterization of GaN nanowires by a catalyst assisted chemical vapor deposition

GaN nanowires have been fabricated on Si(111) substrates by chemical vapor deposition (CVD) method with NiCl2 as catalyst and their compositions, microstructures, morphologies and light emitting properties were characterized by X-ray diffraction (XRD), FT-IR spectrophotometer (FTIR), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), Raman spectroscopy and photoluminescence (PL). The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high crystalline quality, having the size of 20–50nm in diameter and several tens of microns in length with some nano-droplets on their tips, which reveals that the growth mechanism of GaN nanowires agrees with vapor–liquid–solid (VLS) process. Five first-order Raman active phonon bands move to low shift and A1(TO), E1(TO), and E2 (high) bands are overlapped and broaden, which is caused by uncertainty in the phonon wave vector. Five non-first-order active Raman phonons also appear, which is caused by the small dimension and high surface disorder degree. A blue-shift of the band-gap emission occurs due to quantum confinement effect.

Hydrogenated nitrile butadiene rubber and hindered phenol composite. II. Characterization of hydrogen bonding

AbstractThis article reports on the relationship between the variation of hydrogen bonding and macroscopic properties of composites composed of hydrogenated nitrile butadiene rubber (HNBR) and 3,9‐bis {1,1‐dimethyl‐2 [β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl) propionyloxy] ethyl}‐2,4,8,10‐tetraoxaspiro [5,5]‐undecane (AO‐80). Hydrogen bonding of the composites was studied by Fourier‐transform infrared (FT‐IR) and ultraviolet (UV) spectroscopies. FT‐IR spectra at room temperature revealed that the stretching vibration peak of OH and CO of AO‐80 red shifted with increasing AO‐80 content, whereas that of C≡N of HNBR blue shifted only when the AO‐80 content exceeded 10 parts per 100 resin (phr). At elevated temperatures, the shift was the opposite for CO and C≡N bands resulting from hydrogen bonding dissociation. In the UV spectra, the E2 band of benzene ring of AO‐80 exhibited two peaks differing in shape. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

Compass-M1 Broadcast Codes in E2, E5b, and E6 Frequency Bands

With the launch of the compass-M1 satellite on 14 April 2007, China is set to become the latest entrant into global navigation satellite systems (GNSS). Understanding the interoperability and integration of the Chinese Compass with the current GNSS, namely the U.S. Global Positioning System (GPS), the European Galileo, and the Russian GLONASS, requires knowing and understanding its signal structures-specifically its pseudorandom noise (PRN) codes and code structures. Moreover, the knowledge of the code is a prerequisite for designing receivers capable of acquiring and tracking the satellite. More important is determining if the signal may degrade performance of the current GNSS in the form of interference. Finally, we are eager to learn from the code and signal design of our Chinese colleagues. For this research, we set up a 1.8-m dish antenna to collect the broadcast Compass-M1 signals. Even with the dish antenna, the received signal is still weak and buried in thermal noise. We then apply signal processing and are able to extract the PRN code chips out of the noise in all three frequency bands. The PRN codes are thousands of bits long. In addition, we find that the Compass-M1 PRN codes in all frequency bands are Gold codes. We also derive the Gold code generators to represents thousands of code chips with fewer than a hundred bits. Finally, we implement these codes in our software receiver to verify and validate our analysis.

Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epifilms

Crystal symmetry breaking of wurtzite C6V to orthorhombic C2V due to in-plane anisotropic strain was investigated for nonpolar (112¯0) ZnO epifilms grown on the R-sapphire. X-ray diffraction results reveal the epilayer is subjected to a compressive strain along the polar c-axis and tensile strains along both a-[112¯0] surface normal and in-plane p-[11¯00] axis. The polarized Raman spectra of E2 modes reveal violation of the C6V selection rules. Oppositely, the C2V configuration satisfies the selection rules for the Raman modes. The observed E1 and E2 bands in polarized optical reflection and photoluminescence spectra confirm the anisotropic strain causes the structure change to the orthorhombic one.

Lifetimes in E2 bands of 142Gd measured with DSAM at EUROBALL

Lifetimes have been measured for four quadrupole bands in 142Gd with EUROBALL using the Doppler-shift attenuation method. The deduced B(E2) values have been compared with results of Interacting Boson Model calculations.

Lipoprotein metabolism of pregnant women is associated with both their genetic polymorphisms and those of their newborn children

To explore whether the placenta contributes to the lipoprotein metabolism of pregnant women, we took advantage of the fact that placental proteins are encoded from the fetal genome and examined the associations between lipids of 525 pregnant women and the presence, in their newborns, of genetic polymorphisms of LPL and apolipoprotein E (APOE), two genes expressed in placenta. After adjustment for maternal polymorphisms, newborn LPL*S447X was associated with lower triglycerides (-21 +/- 9 mg/dl), lower LDL-cholesterol (LDL-C; -12 +/- 5 mg/dl), lower apoB (-14 +/- 4 mg/dl), higher HDL-C (5 +/- 2 mg/dl), and higher apoA-I (9 +/- 4 mg/dl) in their mothers; newborn LPL*N291S was associated with higher maternal triglycerides (114 +/- 31 mg/dl); and newborn APOE*E2 (compared to E3E3) was associated with higher maternal LDL-C (14 +/- 6 mg/dl) and higher maternal apoB (14 +/- 5 mg/dl). These associations (all P < 0.05) were independent of polymorphisms carried by the mothers and of lipid concentrations in newborns and were similar in amplitude to the associations between maternal polymorphisms and maternal lipids. Such findings support the active role of placental LPL and APOE in the metabolism of maternal lipoproteins and suggest that fetal genes may modulate the risk for problems related to maternal dyslipidemia (preeclampsia, pancreatitis, and future cardiovascular disease).

Effects of periodic delta-doping on the properties of GaN:Si films grown on Si (111) substrates

In this study, the effects of periodic Si delta-doping on the morphological and optical properties of GaN films grown on Si (111) substrate have been investigated. It is found that the flow rate of Si dopant during growth significantly affects the surface morphology, structural and optical quality of GaN. Compared to undoped GaN on Si(111), films grown using periodic delta-doping show a significant reduction of the in plane tensile stress, which is confirmed by the blueshift of the E2(TO) phonon and band edge photoluminescence peaks. The crack density in GaN films also reduces due to delta-doping.

A study of deep levels in vanadium-doped GaAs grown by OMVPE

Vanadium(V)-doped GaAs layers grown by metal organic vapour phase epitaxy using vanadium tetrachloride as a doping source were characterized by deep level transient spectroscopy. The only deep level detected in undoped GaAs is EL2. After V doping, the EL2 defect was not detected. This observation is explained by a reaction involving V and the EL2 arsenic antisite. V doping creates an electron trap (E1) at 0.14 eV below the conduction band, associated with the transition V3+/V2+, and a broad band (E2) of electron traps. The E1 concentration increases with increasing V doping to reach a maximum value of 1016 cm−3 for a total V concentration of about 1018 cm−3. The E2 band is characterized by a defect distribution similar to the so-called U band. We propose that it is associated with intrinsic defects introduced by the growth conditions.

M1 and E2 band structures in the Sn-Xe-Ba region

In the present talk I will discuss some ‘rare’ aspects of the E2 band structures and the novel features concerning the dipole bands in this mass region. Reliable and accurate lifetimes have been measured using coincidence recoil distance method. The results of 129,130Ba will be discussed. In contrast to the predictions of the tilted axis cranking model, the dipole bands in Sb-Xe-Ba nuclei can be nicely described as high-K prolate bands. New data from multi-detector arrays has established extended bands structure, their decay to low lying states have been established and the angular correlation supports the predominant, ΔI=1 character. Finally the sensitive measures, i.e. B(M1) rates of the tilted axis model are compared with the high-K formula based on 1-dim cranking model.

Superdeformed shapes and configurations in thallium nuclei

Superdeformation studies in 189,191,192Tl at Gammasphere are discussed. New results on 191Tl are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment ( Q 0 = 18±1 eb) for these superdeformed structures. These data enable us to derive absolute M1 strengths and confirm that the 81 st proton occupies the [642] 5 2 orbital. Tentative data for one superdeformed sequence in 189Tl are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.

Evidence of unique-parity band structure in neutron-rich odd-A Ru isotopes.

With prompt \ensuremath{\gamma}-ray and x-ray spectroscopy on fission fragments, several new transitions in $^{109,111}\mathrm{Ru}$ have been identified. Angular correlation analysis of several of the new transitions yield evidence of a stretched E2 band structure. Qualitative Nilsson model arguments, systematics, and triaxial rotor+particle calculations support our hypothesis that the observed band is built on the unique parity \ensuremath{\nu}${\mathit{h}}_{11/2}$ orbital.

Tissue-specific expression and preliminary functional analysis of the 5' flanking regions of the human mitochondrial aldehyde dehydrogenase (ALDH2) gene.

Mitochondrial aldehyde dehydrogenase (ALDH2) is a member of a large group of enzymes that catalyze the irreversible oxidation of aldehydes to carboxylic acids. The ALDH2 enzyme has a very low Km (<1 μM) for short aliphatic aldehydes such as acetaldehyde and propionaldehyde. In human beings, this isozyme appears to play a major role in the removal of acetaldehyde generated from the oxidation of ethanol. This conclusion is based on the study of individuals with a genetically determined deficiency in ALDH2 activity. Liver or hair root extracts from these individuals show the absence of the ALDH2 activity band on starch gels or isoelectric focusing gels (also known in the literature as the ALDH I or E2 band) (Harada et al., 1980). The deficiency results from a point mutation that substitutes a lysine for glutamate at position 487 (Yoshida et al., 1984; Crabb et al., 1989). Individuals with the deficient phenotype experience alcohol-induced flushing that is secondary to high levels of circulating acetaldehyde (Harada et al., 1981; Enomoto et al., 1991b). This is commonly referred to as the Oriental alcohol flush reaction. Assays of liver extracts from individuals carrying a deficient allele have about half the aldehyde dehydrogenase activity of extracts from subjects without the deficiency (S.-J. Yin, personal communication). Thus, ALDH2 activity makes a major contribution to the total aldehyde oxidizing capacity of the liver.KeywordsFlank RegionAldehyde DehydrogenaseALDH2 GeneAldehyde Dehydrogenase ActivityGuanidinium IsothiocyanateThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.