Untersuchung gestörter Winkelverteilungen an F19 in ferromagnetischen Gittern

The perturbation of the 197 keV transition angular distribution in F¹⁹ was investigated by time-dependent spin rotation measurements following excitation with a pulsed beam. The recoil implantation technique was used to determine the internal magnetic fields for F¹⁹ in Fe, Co and Ni lattices. The results are:H _HF(F¹⁹ in Fe)=+(95700±500) Oe,H _HF(F¹⁹ in Co)=+(59500±1500) Oe,H _HF(F¹⁹ in Ni)=?(21830±350)Oe. The temperature and field dependence of the effective fields was studied. Strong satellite fields due to lattice perturbations were detected. The half life and the gyromagnetic ratio of the 197 keV 5/2⁺ state in F¹⁹ were redetermined asT _1/2=(80.2±0.5) nsec andg=+1.436±0.007.     

Electronic-excitation transfer collisions in flames—II temperature dependence of the quenching of Na(32P)-doublet by H2 and O2

Effective cross sections for quenching of the Na(3²P)-doublet by H₂ and O₂ molecules have been measured in flames in the temperature range 1500–2500 K. The H₂-cross section decreases from (9.3±1.0) Ų at 1500 K to (6.8±1.0) Ų at 2500 K. The O₂-cross section decreases from (39±2) Ų at 1720 K to (31±2) Ų at 2500 K. A critical comparison of the flame values with previous literature data on the H₂-cross section at lower temperatures shows that it decreases systematically when the temperature rises from about 400 to 2500 K.     

Structures,thermochemistry, and electron affinities of the disilicon fluorides,Si2F n /Si2F− n (n = 1–6)

A systematic investigation of Si₂F_n/Si₂F^? _n systems is carried out with five density functional (DFT) methods in conjunction with DZP++ basis sets. For each system, various structures, including minima, transition states, and energetically low lying saddle points, are optimized. The geometries and the relative energies are discussed and compared. Three kinds of electron affinity and dissociation energy pertaining to the global minimum for each compound are reported. The theoretical predictions are in good agreement with the limited experimental results. The zero-point vibrational energy (ZPVE) corrected adiabatic electron affinities (EA_ad) are predicted as 1.97 (Si₂F), 1.92 (Si₂F₂), 2.39 (Si₂F₃), 2.02 (Si₂F₄), 2.68 (Si₂F₅), and 0.73 (Si₂F₆)eV by the BHLYP method, which is considered to be the most reliable method in the present study for predicting the EAs. These theoretical predictions are quite different from those for the analogous silicon hydrides and fluorocarbons. For example, both Si₂F₂ and its anions have vinylidene-like (Si-SiF₂) global minima. The anion SiSi bond distance is about 0.1 Å shorter than that for the Si—SiF₂ neutral. Both Si₂F₃ and its anion have carbyne-like (Si-SiF₃) global minima, with the anion SiSi distance about 0.05 Å shorter. Both Si₂F₄ and its anion have carbene-like (FSi-SiF₃) global minima, again with the negative ion SiSi distance ～0.05 Å shorter. Surprisingly, doubly bridged structures of Si₂F₄ are energetically competitive. For the ethyl-radical-like Si₂F₅, the expected longer SiSi distance (by 0.13 Å) for the anion is predicted. Whereas Si₂H₄, C₂F₄, Si₂H₆, and C₂F₆ do not have significant electron affinities, Si₂F₄ and Si₂F₆ do bind an electron. However, the unexpected Si₂F^? ₆ species has a significantly longer SiSi distance (by 0.15 Å) than that of neutral Si₂F₆.     

The microwave spectrum of C-fluorophosphaethyne FCP: Structure determination,dipole moment,and vibration-rotation data

The microwave spectrum of the new linear triatomic molecule C-fluorophosphaethyne FCP which is produced when CF₃PH₂ vapor passes over solid KOH at room temperature and ca. 20 μmHg pressure has been studied. Transitions belonging to the two isotopic variants ¹⁹F¹²C³¹P and ¹⁹F¹³C³¹P have been analyzed and the resulting structural data are $\text{r(}\text{FC}\text{) = 1.285 ± 0.005}\text{A}\text{?}$ and $\text{r(}\text{CP}\text{) = 1.541 ± 0.005}\text{A}\text{?}$. The study has yielded the following spectroscopic parameters for ¹⁹F¹²C³¹P: B₀ = 5257.80 ± 0.03 MHz, α₂ = ?11.95 ± 0.05 MHz, q₂ = 4.478 ± 0.002 MHz, and μ = 0.279 ± 0.001 Debye.     

Perturbed angular distribution of recoil implanted F19-nuclei in a nickel-environment

Magnetic hyperfine fields acting on F¹⁹ in a Nickel lattice have been investigated. Time-dependent spin rotation has been observed following the excitation and recoil implantation with a pulsed proton beam using the reaction F¹⁹(p,p′)F¹⁹?. Two hyperfine fields were detected at 290 °K:H _hf ⁽¹⁾ =+17.6 ± 0.5 kGH _hf ⁽²⁾ =+91 ± 3 kG. The variation of the effective fields with the external polarizing field was studied. The mean life of the 197 keV level has been remeasured as τ=128±2 nsec.     

A photoelectron spectroscopic study of the second ionisation of the CF(X2Π) radical

The CF(X²Π) radical has been re-investigated with vacuum ultraviolet photoelectron spectroscopy. Two bands were observed and assigned to the ionisations CF⁺(X¹Σ⁺)←CF(X²Π) and CF⁺(a³Π)← CF(X²Π). The first band, which has been observed previously, has an adiabatic ionisation energy of (9.11±0.02) eV and a vertical ionisation energy of (9.55±0.02) eV. For the second band, three vibrational components were observed with the first, the most intense, at an ionisation energy of (13.94±0.02) eV. Analysis of the vibrational structure in the two observed bands allowed ω_e and r_e to be determined as 1810±30 cm⁻¹ and 1.154±0.005 Å, respectively for the first ionic state, CF⁺(X¹Σ⁺), and 1614±30 cm⁻¹ and 1.213±0.005 Å, respectively for the second ionic state, CF⁺(a³Π). Comparison of the ionisation energies and spectroscopic constants obtained has been made with values obtained from recent multi-reference configuration interaction calculations.     

Direct measurement of bonded film thickness of A20H lubricant

Currently the bonded lubricant thickness is measured either by Fourier transform infrared spectroscopy (FTIR) or electron spectroscopy for chemical analysis (ESCA) on the remaining lubricant after using fluorocarbon solvent like Vertrel to rinse off the mobile lubricant from magnetic disk surfaces. As the thickness of the lubricant applied on a disk approaches to its molecular dimension (～10 Å), the current measurement methods face tremendous challenges in achieving the desired levels of accuracy and sensitivity. We propose a new method that makes use of a time-of-flight mass spectrometry (TOF-SIMS) to directly measure the bonded film thickness of A20H lubricant by quantifying the ratio of either the hydroxyl end-group or the phenoxy portion of the cyclotriphosphazene end-group with respect to their respective neighboring backbone fragments. The quantified ratios include C₂F₃/CF₂CH₂OH and C₆F₃O/CF₃C₆H₄ measured in the positive polarity and C₂F₃O/OCF₂CH₂OH, and C₇F₅/CF₃C₆H₄O₂H₂ measured in the negative polarity. The transfer function from the quantified ratios to the bonded lubricant thickness (t) is given in the form of t=α×ln?(100×R _T )?β, where α,β are constants for a selected ratio and R _T represents the quantity of the specific ratio. The results correlate very well with the FTIR method currently used in the measurement of the magnetic media during production (R ²>90). The new method can complete the measurement of the bonded lubricant thickness in a one-step process and it has a much higher spatial resolution at sub-micrometers than that of the FTIR or ESCA with order of a few tens of micrometers in resolution. The quantified ratio obtained from this TOF-SIMS technique makes the imaging of the localized bonded lubricant possible, which can be applied in the magnetic media failure analysis.     

Excitation and dissociation of polyatomic molecules under the action of femtosecond infrared laser pulses

The effect of high-intensity femtosecond laser pulses (100–200 fs) in the near (0.8–1.8 μm) and medium (4.6–5.8 μm) IR ranges on the CF₂HCl, CF₃H, (CF₃)₂C=C=O, and C₄F₉COI molecules is examined. Irradiation of CF₂HCl and CF₃H molecules by 0.8-to 1.8-μm laser pulses with intensities of >40 TW/cm² (>4 × 10¹³ W/cm²) makes them dissociate to yield CF₃H and CF₄, respectively. The key mechanism of the dissociation of these molecules is field ionization and fragmentation. The excitation of the stretching vibrations of the C=O bond in the (CF₃)₂C=C=O and C₄F₉COI molecules by 4.5-to 5.8-μm femtosecond pulses produced no detectable dissociation up to a fluence of ∼0.5 J/cm² (or a intensity of ∼2.5 TW/cm²). Probable explanations of this observation are discussed. Original Russian Text ? V.M. Apatin, V.O. Kompanets, V.B. Laptev, Yu.A. Matveets, E.A. Ryabov, S.V. Chekalin, V.S. Letokhov, 2007, published in Khimicheskaya Fizika, 2007, Vol. 26, No. 4, pp. 18–25.     

克里奇中间体CH2OO与CF3CF=CF2反应的动力学研究

本文使用OH激光诱导荧光方法研究了结构最简单的克里奇中间体CH₂OO和CF₃CF=CF₂的反应动力学. 在压强为10 Torr条件下，测量了温度在283，298，308和318 K的反应速率常数，分别为(1.45±0.14)×10^-13，(1.18±0.11)×10^-13，(1.11±0.08)×10^-13和(1.04±0.08)×10^-13 cm³·molecule^-1·s^-1. 根据阿伦尼乌斯方程，获得该反应的活化能为(-1.66±0.21) kcal/mol. 在6.3∽70 torr压力范围内，未观察到该反应的速率常数存在压力相关.     

The mechanism of formation of the hydroperoxyl radical in the CF<Subscript>3</Subscript>COOH + <Superscript>3</Superscript>O<Subscript>2</Subscript> system: a quantum-chemical study

Ab initio quantum-chemical calculations of the (CF₃CO₂H₂⁺…³O₂) and (CF₃CO₂⁻…³O₂) complexes were performed by the MP2 method. It was found that these complexes were characterized by low complex formation energies, of 2.97 and 1.72 kcal/mol, respectively. According to the MP2(full)/6-311++G(d, p) calculation data, the bridge stabilization of oxygen by linking with both the CF₃CO₂H₂⁺ cation and CF₃CO₂⁻ anion is much more favorable energetically. A study of the potential energy surface of the joint molecular system (CF₃CO₂H₂⁺…³O₂…CF₃CO₂⁻) shows that proton experiences activationless transfer from the cation to the ³O₂ molecule accompanied by electron transfer from the CF₃COO⁻ anion. An analysis of spin density distribution shows that two radicals are stabilized in the (CF₃CO₂….OOH….O=C(OH)CF₃) complex in the triplet state observed on the potential energy surface.     

High pressure tuning of optical transitions in Mg[Pt(CN)4]·7H2O

Mg[Pt(CN)₄]·7H₂O belongs to the class of tetracyanoplatinates(II) which crystallize in columnar structures. In different M_x[Pt(CN)₄]·yH₂O (MCP) single crystals the in-chain Pt-Pt-distance R varies between 3.67 Å (NaCP) and 3.15 Å (MgCP). Two optical transitions can be observed in polarized emission with the electric field vector E either parallel or perpendicular to the columnar (c)-axis. Polarized emission spectra of MgCP are recorded under hydrostatic pressure up to p ≈ 18 kbar (at 295 K). The transition energy v?₆ can be tuned from 17,600 cm^-1 to about 12,000 cm^-1 (2.18-1.48 eV). The pressure induced red shift for the two transitions is: E 6 c: dv?₆/dp = -320±20 cm^-1/kbar, E ⊥ c: dv?_⊥/dp = -270±20 cm^-1/kbar. These values are discussed in the context of the known functional relationship (for ambient conditions) between v? and R.     

Photoabsorption cross sections for chlorinated methanes and ethanes between 46 and 100 Å

Photoabsorption cross sections for the methanes CCl₄, CCl₃F, CCl₂F₂, CClF₃, CF₄, CHClF₂, CHCl₂F and the ethanes C₂F₆, C₂ClF₅, C₂Cl₂F₄ were measured between 46 and 100 Å. In particular, the 0.2 Å resolution provides some insight into the Cl 2p absorption process. It is noted that the molecular cross section for all 8 Cl-containing gases display an L edge “discontinuity” of 3.55±0.15 Mb per Cl atom. The experimental molecular cross sections are compared with sums of atomic cross sections at 100 Å using both theoretical and empirical atomic values. The sums of theoretical atomic cross sections describe every experimental molecular value to better than 10%. The sums of empirical atomic cross sections describe molecular values to within 2%.     

Preparation of superhydrophobic films on titanium as effective corrosion barriers

Stable superhydrophobic films were prepared on the electrochemical oxidized titania/titanium substrate by a simple immersion technique into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltriethoxysilane [CF₃(CF₂)₅(CH₂)₂Si(OCH₂CH₃)₃, PTES] for 1 h at room temperature followed by a short annealing at 140 °C in air for 1 h. The surface morphologies and chemical composition of the film were characterized by means of water contact angle (CA), field emission scanning electron microscopy (FESEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The water contact angle on the surface of this film was measured to be as high as 160°. SEM images showed that the resulting surfaces exhibited special hierarchical structure. The special hierarchical structure along with the low surface energy leads to the high surface superhydrophobicity. The corrosion resistance ability and durance property of the superhydrophobic film in 3.5 wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). The anticorrosion properties of the superhydrophobic film are compared to those of unmodified pure titanium and titania/titanium substrates. The results showed that the superhydrophobic film provides an effective corrosion resistant coating for the titanium metal even with immersion periods up to 90 d in the 3.5 wt.% NaCl solution, pointing to promising future applications.     

Molekularstrahlmessungen von Stoßquerschnitten für Übergänge zwischen definierten Rotationszuständen zwei-atomiger Moleküle

Inelastic collision cross sections for transitions between specified rotational states designated by (J, M) have been measured in a molecular beam apparatus. With an electrostatic four pole field molecules in a specified rotational state are separated out of a molecular beam and focussed into a gas filled scattering chamber. Molecules which have been scattered by less than 1/2° are then collected in a second four pole field, located directly behind the scattering chamber, and are analyzed for their rotational state. From a comparison of the measured pressure dependence with calculated curves a determination of inelastic collision cross sections for specified quantum jumps is possible. Measured inelastic scattering cross sections for the transitions (2,0→3,0) are reported for the gases He, Ne, Ar, Kr, CH₄, SF₆, H₂, O₂, Air, N₂O, H₂O, CF₂Cl₂. The values range between about 5 and 100 Ų in the order indicated. The scattering gases NH₃ und ND₃ yielded larger cross sections of about 600 Ų and, in addition, the transitions (3,0)→(2,0),(1,0)→(2,0), (2,0)→(1,0) and (3,0)→(1,0) were observed. Total cross sections for the same gases were also measured with the apparatus.     

Synthesis,Crystal Structure,Hirshfeld Surface Analysis,and Physicochemical Study of an Anhydrous Organic Acidic Cyclohexaphosphate

The new organic–inorganic hybrid [5-Cl-2-(CH₃)C₆H₃NH₃]₄H₂P₆O₁₈ has been synthesized by the slow evaporation method. X-ray diffraction on a single crystal shows that this acidic cyclohexaphosphate crystallized in the monoclinic space group C _2/c with a?=?33.89(11) Å, b?=?9.16(16) Å, c?=?13.68(3) Å, β?=?91.35(2)°, V?=?4244.9(19) ų and Z?=?4. ³¹P MAS-NMR and ¹³C CP/MAS-NMR results are in accordance with X-ray findings. Fluorescent study shows the blue photoluminescence. Furthermore, FT-IR analysis was studied and the complete vibrational assignments were done. Intermolecular interactions were analyzed using Hirshfeld surface analysis and the associated 2D fingerprint plots.     

Polarized absorption spectra and spectroscopic parameters of Tm3+ in the TmAl3(BO3)4 single crystal

High-optical-quality single crystals of the TmAl₃(BO₃)₄ compound were synthesized from a solution in the melt. The absorption spectra in the σ and π polarizations for the ³ H ₆ → ³ F ₄, ³ H ₆ → ³ H ₅, ³ H ₆ → ³ H ₄, ³ H ₆ → ³ F ₃, ³ H ₆ → ³ F ₂, ³ H ₆ → ¹ G ₄, and ³ H ₆ → ¹ D ₂ transitions in the Tm³⁺ ion were recorded at room temperature. The transition intensities were analyzed in the framework of the Judd-Ofelt theory generalized to the case of anisotropic crystals, and the following parameters of the theory were obtained: Ω₂ = 6.14 × 10^?20 cm², Ω₄ = 3.09 × 10^?20 cm², and Ω₆ = 2.04 × 10^?20 cm². The lifetimes and the branching ratios were determined for all possible transitions.     

Spin inversion in trigonal centers of CaF2:Dy3+

Abstract

Magnetic circular dichroism in the 4431 Å absorption line of the oxygen compensated CaF₂:Dy³⁺ crystal has been used to measure transient phenomena in the Kramers doublet ground level ⁶H_15/2 of the Dy³⁺ ion during magnetic field reversal. After inverting the field with a rate 10 T·s^?1 <dB/dt < 400 T·s^?1 a considerable spin inversion with the final electron spin polarization P_F was achieved while P_F=-0.86±0.03 relaxed to less than 0.05 when dB/dT < 10^?2 T·s^?1.     

Manifestation of resonance dipole-dipole interaction in spectra of low-temperature molecular mixtures of C2F6 in CF4 and CF4 in C2F6

We have measured IR absorption spectra of solutions C₂F₆ in CF₄ (T = 178 K) and CF₄ in C₂F₆ (T = 173 K) in the overtone range of the spectrum. We have studied how the resonance dipole-dipole interaction affects the formation of contours of bands that correspond to transitions to states involving the vibrations ν₁₀(C₂F₆) and ν₃(CF₄), which are strong in the dipole absorption. For the system C₂F₆ in liquid CF₄, the state ν₂ + ν₁₀(C₂F₆) resonantly interacts with the state ν₂(C₂F₆) + ν₃(CF₄), and, for the system CF₄ in liquid C₂F₆, the state ν₁ + ν₃(CF₄) resonantly interacts with the state ν₁(CF₄) + ν₁₀(C₂F₆). The contours of the bands ν₂ + ν₁₀ (C₂F₆) in the spectrum of the mixture with CF₄ and of the bands ν₁ + ν₃(CF₄) in the spectrum of the mixture with C₂F₆ have been calculated.     

High-precision evaluation of the magnetic moment of the helion

NMR spectra of samples containing a mixture of hydrogen deuteride HD with pressure of about 80 atm and helium-3 with partial pressure of about 1 atm are analyzed. The ratio of the resonance frequencies of the nuclei, F(³He)/F(H₂), is determined to be 0.761786594(2), which is equal to the magnetic moment of the helion (bound in a helium atom) in the units of the magnetic moment of a proton (bound in molecular hydrogen). The uncertainty of two digits in the last place corresponds to a relative error of ??[F(³He)/F(H₂)] = 2.6 × 10^?9. The use of the known calculated data on the shielding of nuclei in the helium-3 atom (??(³He) = 59924(2) × 10^?9) and on the shielding of protons in hydrogen (??(H₂) = 26288(2) × 10^?9) yields a value of ??(³He)/?? _p = ?0.761812217(3) for the free magnetic moment of the helion in the units of the proton magnetic moment.     

Quenching of excited strontium atomic state measured in H2- and CO-flames

The efficiency of resonance fluorescence, Y, of the strontium resonance line (¹P₁→¹S₀ transition) at 4607.33 Å was measured in CO/N₂O, CO/O₂/Ar, and H₂/O₂/CO₂/N₂ flames at atmospheric pressure. From these data, the specific quenching cross sections, σ_qu, for CO₂ and CO were found to be (60 ± 10) Ų and  (300 ± 60) Ų, respectively. The experimental cross sections were confronted with the intermediate ionic-state curve-crossing model and chemical quenching model, respectively.