Spectra Of HF Research Articles

A DFT study of (La2O3)n clusters and effect of Ba, Y and Hf doping for their optoelectronic applications

( La 2 O 3 ) n (n=1-5) clusters have been computationally studied using DFT and TDDFT with B3LYP functional under hybrid GGA approximation and LANL2DZ basis set. The doping effect of various elements like Ba, Y and Hf on the structural, electronic and non-linear optical (NLO) properties of ( La 2 O 3 ) n clusters has been studied for finding their optoelectronic applications. Different optimised geometries of ( La 2 O 3 ) n and Ba, Y and Hf doped ( La 2 O 3 ) n clusters have been obtained. HOMO-LUMO gap ( Δ E ) and chemical hardness (τ) of ( La 2 O 3 ) n clusters decreases significantly with doping of Ba, Y and Hf atoms making these clusters very reactive. Refractive index and the absorption in UV–VIS region of electromagnetic spectra of Ba, Y and Hf doped ( La 2 O 3 ) n clusters increases as compared to ( La 2 O 3 ) n clusters making these clusters suitable to be used as additives in the manufacturing of various types of glasses. Also, dielectric constant (ϵ) of Ba, Y and Hf doped ( La 2 O 3 ) n clusters increases finding their applications to be used in the oxide layer of MOSFETs.

HF, DF, TF: approximating potential curves, calculating rovibrational states

A simple analytical expression for the potential energy curve for the ground state X 1Σ+ of the hydrogen fluoride molecule HF obtained in the framework of the Born–Oppenheimer approximation is proposed. This analytical expression for the potential energy curve is based in the two point Padé approximation, which correctly reproduces the asymptotic behavior at small R → 0 and large R → ∞ internuclear distances, and position and depth of potential well, leading to the accuracy of 4–5 decimal digits when compared with experimental data. The rovibrational spectra of the diatomic molecule HF is calculated by solving the Schrödinger equation for nuclear motion using the Lagrange-mesh method. The ground state X 1Σ+ contains 21 vibrational states (ν, 0) and 724 rovibrational states (ν, L) with maximal angular momentum equal to 55. The change of reduced mass in the Schrödinger equation for nuclear motion allows us to obtain the rovibrational spectrum of the ground state potential curve of the deuterium fluoride DF (contains 29 vibrational states (ν, 0) and 1377 rovibrational states (ν, L)) and tritium fluoride TF (contains 35 vibrational states (ν, 0) and 1967 rovibrational states (ν, L)) with maximal angular momenta 76 and 92, respectively. Entire rovibrational spectra is presented for the HF molecule and its two isotopologues DF and TF.

Theoretical and matrix isolation studies of infrared spectra of the H2CO∙∙∙HF hydrogen-bonded complex

The equilibrium geometry, the binding energy, and harmonic and anharmonic spectral parameters of H2CO and HF monomers and the H2CO∙∙∙HF complex are calculated in the MP2/6-311++G(3df,3pd) approximation with the basis set superposition error taken into account. Anharmonic calculations are carried out using the second-order vibrational perturbation theory. The changes in transition frequencies and intensities of monomeric IR bands upon formation of the 1:1 complex are analyzed. A high intensity value (53 km mol–1) is predicted for the overtone band of the out-of-plane HF libration. The variational method was used to solve anharmonic vibrational problems in 1D–4D subspaces involving the H–F stretch. The influence of anharmonicity on spectral and structural parameters was studied. The variational calculation confirmed the high intensity value for the overtone of the HF librational mode from the perturbative calculation. Matrix-isolation experiments were performed in N2 at T = 8 K to record the absorption spectra of pure H2CO and HF and H2CO/HF mixtures in the IR region. The spectral features related to the H–F, C=O, and C–H stretches and the in-plane HF librational motion were reliably identified. The predictions of our perturbative calculations for isolated compounds, especially for the band shifts upon complexation, are in satisfactory agreement with the experimental matrix-isolation findings. The only exception is the H–F stretching mode in the complex because of the high anharmonicity of HF and strong interaction of free HF molecules with a matrix environment. Of particular interest is the observation of a rather strong band at 1069 cm–1, which is close to 1072 cm–1 predicted for the overtone of HF out-of-plane librational mode.

Effect of [Li]/[Nb] ratios on UV-VIS-NIR spectroscopy and up-conversion luminescence in Hf:Dy:LiNbO3 crystals

A series of Hf:Dy:LiNbO3 crystals with various [Li]/[Nb] ratios ([Li]/[Nb]=0.946, 1.05, 1.20 and 1.38) in the melt were grown by the Czochralski method. The UV-VIS-NIR absorption spectra of Hf:Dy:LiNbO3 crystals were measured, and Judd-Ofelt (J-O) theory is used to evaluate the transition intensity parameters Ω2, 4, 6 and spectroscopic quality factor (X). The X of Hf:Dy:LiNbO3 crystals with the [Li]/[Nb] ratio of 1.38 was found to be 2.11. The up-conversion luminescence at around 475 nm, 582 nm, 653 nm and 749 nm of Dy3+ ions were observed under 800 nm excitation. The energy transfer mechanisms of up-conversion process were analyzed in detail, and luminescence lifetime was measured. The results show that Hf:Dy:LiNbO3 crystal is an excellent candidate for laser medium.

On the structural features of iron-phosphate glasses by Raman and EPR: Observation of superparamagnetic behavior differences in HfO2 or CeO2 containing glasses

Structural features of hafnium or cerium doped iron borophosphate glasses have been studied by Raman and EPR spectroscopies. Hf and Ce are introduced into the composition as surrogates for Pu. Raman spectrum of Hf and Ce free base iron phosphate glass indicate that the glass network consisted mainly of Q1 units with contributions from Q2 units. The general features observed for base glass are maintained in the Raman spectra of Hf/Ce containing glasses with some modifications with increasing Ce/Hf content in the composition. The EPR spectra of Hf and Ce containing glasses show different features. Superparamagnetic domains were highlighted through EPR for all CeO2 containing glasses.

Effect of Hf4+ doping on structure and enhancement of upconversion luminescence in Yb:Tm:LiNbO3 crystals**Project supported by Special Funds of Harbin Innovation Talents in Science and Technology Research, China (Grant No. 2015RQQXJ045) and Science Funds for the Young Innovative Talents of HUST, China.

A series of Yb:Tm:LiNbO3 crystals doped with x mol% Hf4+ ions (x = 2, 4, and 6) were grown by the Czochralski method. The dopant occupancy and defect structure of Hf:Yb:Tm:LiNbO3 crystals were investigated by x-ray diffraction and infrared transmission spectra. The influence of Hf4+ ions concentration on UV–VIS–NIR absorption spectra of Hf:Yb:Tm:LiNbO3 crystals was discussed. The upconversion luminescence of Hf:Yb:Tm:LiNbO3 crystals was obtained under 980 nm excitation. Strong emissions were observed at 475 nm in the blue wavelength range and 651 nm in the red wavelength range. Remarkably, enhancement of the red and blue upconversion luminescence was achieved by tridoping Hf4+ ions.

Far-infrared study of tracers of oxygen chemistry in diffuse clouds

Context. The chemistry of the diffuse interstellar medium rests upon three pillars: exothermic ion-neutral reactions (" cold chemistry "), endothermic neutral-neutral reactions with significant activation barriers (" warm chemistry "), and reactions on the surfaces of dust grains. While warm chemistry becomes important in the shocks associated with turbulent dissipation regions, the main path for the formation of interstellar OH and H2O is that of cold chemistry. Aims. The aim of this study is to observationally confirm the association of atomic oxygen with both atomic and molecular gas phases, and to understand the measured abundances of OH and OH + as a function of the available reservoir of H2. Methods. We obtained absorption spectra of the ground states of OH, OH+ and OI with high-velocity resolution, with GREAT on-board SOFIA, and with the THz receiver at the APEX. We analyzed them along with ancillary spectra of HF and CH from HIFI. To deconvolve them from the hyperfine structure and to separate the blend that is due to various velocity components on the sightline, we fit model spectra consisting of an appropriate number of Gaussian profiles using a method combining simulated annealing with downhill simplex minimization. Together with HF and/or CH as a surrogate for H2, and HI $\lambda$21 cm data, the molecular hydrogen fraction f^N\_H2 = N(H 2)/(N(H) + 2N(H 2)) can be determined. We then investigated abundance ratios as a function of f^N\_H2. Results. The column density of OI is correlated at a high significance with the amount of available molecular and atomic hydrogen, with an atomic oxygen abundance of $3 \times 10 ^{-4}$ relative to H nuclei. While the velocities of the absorption features of OH and OH+ are loosely correlated and reflect the spiral arm crossings on the sightline, upon closer inspection they display an anticorrespondence. The arm-to-interarm density contrast is found to be higher in OH than in OH+. While both species can coexist, with a higher abundance in OH than in OH+, the latter is found less frequently in absence of OH than the other way around, which is a direct consequence of the rapid destruction of OH+ by dissociative recombination when not enough H2 is available. This conjecture has been substantiated by a comparison between the OH/OH+ ratio with f^N\_H2, showing a clear correlation. The hydrogen abstraction reaction chain OH+ (H2,H) H2O+ (H2,H)H3O+ is confirmed as the pathway for the production of OH and H 2 O. Our estimate of the branching ratio of the dissociative recombination of H3O+ to OH and H2O is confined within the interval of 84 to 91%, which matches laboratory measurements (74 to 83%). -- A correlation between the linewidths and column densities of OH+ features is found to be significant with a false-alarm probability below 5%. Such a correlation is predicted by models of interstellar MHD turbulence. For OH the same correlation is found to be insignificant because there are more narrow absorption features. Conclusions. While it is difficult to assess the contributions of warm neutral-neutral chemistry to the observed abundances, it seems fair to conclude that the predictions of cold ion-neutral chemistry match the abundance patterns we observed.

Structure and properties of hafnium iron borophosphate glass-ceramics

Effects of hafnium addition on the structure and properties of iron borophosphate glasses with nominal composition of xHfO2–yB2O3–[40–(x+y)]Fe2O3–60P2O5 (x=0–8, mol%) and xHfO2–yB2O3–[40–(x+y)][40Fe2O3–60P2O5] (x=2–6, mol%) have been investigated by XRD, DTA, IR, SEM and Mössbauer spectroscopy. There were some surface crystallizations on some of the samples containing high amounts of Hf and B. XRD spectra revealed that HfP2O7 crystallized in the glass matrix when HfO2 content was above 2mol% even when there was no surface crystallization and samples looked glassy. SEM-EDAX image-analyses supported the formation of the HfP2O7 phase. Dissolution rates of Hf-containing iron borophosphate glasses were in the 10−9–10−10g/cm2min range which shows that the existence of the crystalline HfP2O7 phase in the glass matrix has not degraded the aqueous chemical durability of these glasses. The band observed at ~984cm−1 in the IR spectra of Hf containing samples was attributed to the Hf–O–P bonds in HfP2O7. Iron existed in two valence states, i.e. Fe2+ and Fe3+ and Mössbauer hyperfine parameters indicated that both ions have octahedral coordinations in the samples studied.

Study on Bearing Impedance Properties at Several Hundred Kilohertz for Different Electric Machine Operating Parameters

The possibility of bearing damage caused by inverter-induced bearing currents in modern variable-speed drive systems has been well recognized. However, the breakdown and current conduction mechanisms have still not been well understood today. We present results on the HF impedance properties of rolling element bearings at 300-kHz and 1.5-MHz signals-frequencies taken from the typical spectra of HF circulating bearing currents. Different motor speeds, bearing temperatures, voltages across the bearing, and two different motor sizes are investigated. Notably, we analyze the frequency of transitions between ohmic and capacitive behavior (or vice versa)-the “mode transitions”-as a function of these operating parameters: For some operating conditions, the bearing impedance alternates between capacitive and ohmic behavior without any modification of the macroscopic conditions it is subjected to.

Strong intermolecular coupling between the HF stretching and H2O bending vibrations in HF:H2O binary amorphous solids: Breakdown of the electrostatic description of the hydrogen bond

The coupling mechanism between the HF stretching and H(2)O bending vibrations observed in the infrared spectra of HF:H(2)O binary amorphous solids is analyzed using a simple cluster model. The intermolecular vibrational coupling derived from electrostatic potentials is one order of magnitude smaller, and of the opposite sign, than that obtained from electronic structure-based potentials. This highlights the distinctively covalent character of strong H-bonds and unveils fundamental weaknesses of electrostatic descriptions of vibrational energy transfer in liquid water and aqueous solutions.

Simultaneous analysis of rotational and vibrational–rotational spectra of DF and HF to obtain irreducible molecular constants for HF

Analytic expressions of corrections for the breakdown of the Born–Oppenheimer approximation to Dunham’s Y ij with optimal parameters, i.e., determinable clusters of expansion coefficients, are applied to a data analysis of the rotational and vibrational–rotational transitions of HF reported in the literature. All the available spectral lines of the two isotopologues, DF and HF, are simultaneously fitted to a single set of molecular parameters of HF within experimental errors. Fitting of a data set of 595 spectral transitions for DF and HF has generated only 20 minimal independent parameter values, i.e., “irreducible” molecular constants of HF, that are sufficient to precisely generate 82 Y ij coefficients and 144 band constants in total: 41 Y ij and 72 band constants each for DF and HF.

Schumann Resonance Measurement Based on Nonlinear Interaction

Schumann Resonance relates with global temperature variations, new geophysics phenomena in the low ionosphere and short-term earthquake prediction etc. In this paper based on the nonlinear modulation model of high frequency and extreme-low frequency electromagnetic waves in low ionosphere, the Schumann Resonance observing is researched. Taking the fair weather electric field in account, the cross modulation index was 4.2×10-4. At the first Schumann Resonance observatory of China, the first 4 peaks of Schumann Resonance respectively at 7, 14, 20, 26Hz were obtained in demodulation spectra of the high frequency time service signals. The parameter characteristics of Schumann Resonance in the low ionosphere were analyzed under the geographical condition of middle latitude area. The feasibility of Schumann Resonance measurement by demodulating the spectra of HF has been verified. The non-linearity between Schumann Resonance and very low frequency signals also was discussed.

Radioluminescence and photoluminescence of hafnia-based Eu-doped phosphors

Crystal structures of hafnia are discussed and it is shown that addition of about 7 at.% of Lu to the HfO 2 host lattice enforces the mixed composition to crystallize in cubic structure even at room temperature. Without Lu HfO 2 crystallizes in monoclinic structure. Luminescence and luminescence excitation spectra of Hf 0.93Lu 0.07O 1.965 are presented and discussed for powders prepared at different temperatures (600–1000 °C) and with different content of Eu. It is shown that decay of the 595.4 nm luminescence is longer (2.5 ms) than the 610 nm (1.6 ms). Radioluminescence efficiency of the cubic Hf 0.93Lu 0.07O 1.965 is low and does not exceed 10% of the commercial Gd 2O 2S:Eu.

XAFS of Pu and Hf LIII Edge in Lanthanide-Borosilicate Glass

AbstractLanthanide-Borosilicate (LaBS) glass capable to dissolve up to ∼10 wt.% PuO2 is designed for immobilization of plutonium-bearing wastes. The sample of LaBS glass with a target chemical composition (wt %): 9.0 Al2O3, 11.8 B2O3, 12.2 Gd2O3, 6.3 HfO2, 17.2 La2O3, 13.6 Nd2O3, 9.5 PuO2, 18.1 SiO2, 2.3 SrO was prepared from PuO2 powder and mechanically activated mixture of chemicals at 1500 °C. The obtained product was visually homogeneous. Xraydiffraction of the as-prepared glass showed that it mostly consists of a vitreous phase withsmall amounts of crystalline PuO2 (or PuO2-HfO2 solid solution with minor HfO2), britholite andan oxide with a fluorite structure and a composition close to GdHfO1.75. The crystalline fractionincreased after storage for ∼1 year. Magnitude of the FT of EXAFS spectrum at Pu LIII edgeshows that the peak due to first coordination sphere is much more intense than that of the secondshell. This indicates that though some Pu entered crystalline phases (mainly distorted PuO2), itsmajor fraction remained in the vitreous phase. Fit of the spectrum (R-factor = 0.02) gives thefollowing distances: R (Pu-O1)1 = 1.98 (σ = 0.04), R (Pu-O1)2 = 2.18 (σ = 0.04), R (Pu-O1)3= 2.35, R (Pu-Pu) = 3.72 (σ = 0.04), R (Pu-O2) = 4.4 (σ = 0.06). Oxygen environment ofthe Pu4+ ions in the vitreous phase resembles axially squeezed tetragonal pyramid with acoordination number ∼5. The distances ∼2.35 and ∼4.4 correspond to the pairs Pu-O in thefirst and the second shells in the crystalline PuO2. The distance ∼3.72 corresponds to the Pu-Pu and/or Pu-M (M = Ln, Hf) distances. EXAFS spectra of Hf show that Hf is present mostly in thevitreous phase with major neighbors at 2.17 and ∼3.2 A.

On the effects of basis-set in studying the hydration and dissociation of HF in cubic HF(H 2O) 7 clusters

We have carried out a systematic study on the performance of Pople-style basis functions on the structure, electronic energies, vibrational spectra of the cubic HF(H 2O) 7 clusters with B3LYP method. Molecular structure and relative energy among the orientational isomers converge quickly with respect to the basis set and we found that, for most of the purposes, 6-311+G(d,p) represents the most economic choice to yield reliable results. Studies on the potential energy surface for the HF dissociation reactions show that smaller basis set tends to favor fluoric acid dissociation and the barrier height is sensitive to the basis set.

Energetics and dynamics of threshold photoion-pair formation in HF∕DF

Threshold ion-pair production spectroscopy (TIPPS) has been applied to two isotopomers, HF and DF. From the high resolution (approximately 0.3 cm(-1)) TIPP spectra, the ion-pair thresholds of HFDF have been precisely measured. Combined with the ionization energy of H(D), the electron affinity of F, and the zero point energies of HFDF, the difference between their classical bond dissociation energies was obtained as D(e)(H-F)-D(e)(D-F) = 12.4 +/- 0.5 cm(-1). Our result provides an experimental estimate of the Born-Oppenheimer breakdown in the ground electronic state. The present work also measured the total ion-pair yield spectra of HF and DF in the threshold region, and the ion-pair formation mechanisms of these two molecules were discussed in light of the high resolution results.

Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy

Following the photodissociation of o-fluorotoluene [o-C(6)H(4)(CH(3))F] at 193 nm, rotationally resolved emission spectra of HF(1< or =v< or =4) in the spectral region of 2800-4000 cm(-1) are detected with a step-scan Fourier transform spectrometer. HF(v< or =4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature approximately 1080 K; a short extrapolation from data in the period of 0.5-4.5 mus leads to a nascent rotational temperature of 1130+/-100 K with an average rotational energy of 9+/-2 kJ mol(-1). The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330+/-270 K. An average vibrational energy of 25+/-(3) (12) kJ mol(-1) is derived based on the observed population of HF(1< or =v< or =3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C(6)H(4)(CH(3))F] yielded similar results with an average rotational energy of 9+/-2 kJ mol(-1) and vibrational energy of 26+/-(3) (12) kJ mol(-1) for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis.

Density functional calculation of K-shell spectra of small molecules

Both Δ E KS and time-dependent density functional theory (TD-DFT) methods, with approximations for the singlet–triplet splitting and for the relativistic corrections, were tested for the calculation of K-shell spectra of Ne, HF, H 2O, NH 3, CH 4, and CO. Results from several exchange-correlation functionals as well as diffuse basis sets were compared with available experimental data. Excellent core excitation and core-electron ionization energies for Ne, HF, H 2O, NH 3, CH 4, and CO can be obtained from Δ E with Perdew–Wang 1986 exchange and Perdew–Wang 1991 correlation functionals; and reasonable intensities for singlet excitations, from TD-DFT with exchange-correlation potential known as statistical average of orbital potentials. The dependence of the quality of Δ E on basis set is as expected: excitations to higher Rydberg levels requiring more diffuse functions. However, the oscillator strength seems to be more sensitive to the quality of the basis set. Suggestions are made for extending the procedure to larger systems.

Molecular elimination in photolysis of fluorobenzene at 193 nm: Internal energy of HF determined with time-resolved Fourier-transform spectroscopy

Following photodissociation of fluorobenzene (C(6)H(5)F) at 193 nm, rotationally resolved emission spectra of HF(1<or= v <or= 4) in the spectral region 2800-4000 cm(-1) are detected with a step-scan Fourier-transform spectrometer. In the period 0.1-1.1 mus after photolysis, HF(v <or= 4) shows similar Boltzmann-type rotational distributions corresponding to a temperature approximately 1830 K; a short extrapolation from data in the period 0.1-4.1 mus leads to a nascent rotational temperature of 1920+/-140 K with an average rotational energy of 15+/-3 kJ mol(-1). The observed vibrational distribution of (v = 1):(v = 2):(v = 3):(v = 4) = (60+/-7):(24+/-3):(10.5+/-1.2):(5.3+/-0.5) corresponds to a vibrational temperature of 6400 +/- 180 K. An average vibrational energy of 33 +/- 9/3 kJ mol(-1) is derived based on the observed population of HF(1 <or= v <or= 4) and an estimate of the population of HF(v = 0) by extrapolation. The observed internal energy distribution of HF is consistent with that expected for the four-center (alpha,beta) elimination channel. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. We also compare internal energies of HF observed in this work with those from photolysis of vinyl fluoride (CH(2)CHF) and 2-chloro-1,1-difluoroethene (CF(2)CHCl) at 193 nm.

Three-center versus four-center elimination of haloethene: Internal energies of HCl and HF on photolysis of CF2CHCl at 193 nm determined with time-resolved Fourier-transform spectroscopy

Following photodissociation of 2-chloro-1,1-difluoroethene CF2CHCl) at 193 nm, vibration–rotationally resolved emission spectra of HCl(v⩽3) and HF(v⩽4) in spectral regions 2000–2900 and 3050–4410 cm−1, respectively, are detected with a step-scan time-resolved Fourier-transform spectrometer. All vibrational levels of HCl and HF show Boltzmann-type rotational distributions. HCl has an average rotational energy of 23±4 kJ mol−1 and a vibrational energy of 25±5 kJ mol−1, whereas HF has an average rotational energy of 20±4 kJ mol−1 and a vibrational energy of 48±6 kJ mol−1. The observed internal energy distribution indicates that HCl is produced via the three-center (α,α), but HF via the four-center (α,β) elimination. A modified separate statistical ensemble model predicts an internal energy distribution of HCl slightly greater than experimental observation. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF produced from four-center elimination. Ratios of rate coefficients (0.87:0.13) predicted for three-center or four-center elimination channels based on Rice–Ramsperger–Kassel–Marcus theory are consistent with a branching ratio of 0.88:0.12 determined based on observed populations of HCl and HF, respectively. We also compare these experimental and theoretical results with those of photolysis of vinyl halides (CH2CHX, X=F, Cl, or Br) at 193 nm.