Fine and hyperfine structure in 14N2+

The fine and hyperfine structure of ¹⁴N₂⁺ has been observed in 31 rotational lines of the (0, 1) band of the B²Σ_u⁺-X²Σ_g⁺ system using the method of Doppler-tuned laser-induced fluorescence on a molecular ion beam. The spin-rotation constants (γ′, γ″, γ′_J) are in good agreement with other experiments in which the hyperfine structure was not resolved. The Fermi-contact (b′_F, b″_F) and dipolar (t′, t″) hyperfine coupling constants are in reasonably good agreement with values calculated from ab initio wavefunctions. The least-squares experimental values in MHz are γ″ = 279.1(6), γ′ = 726.4(6), γ′_J = ?0.0460(2), b″_F = 105(4), b′_F = 708(3), t″ = 49(6), and t′ = 26(5).     

Combined use of small-angle neutron scattering and atom probe tomography for the analysis of precipitates in a Fe-15 m% Co-25 m% Mo alloy

Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy. Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed.     

Vacancy induced changes in the electronic structure of titanium carbide—I. Band structure and density of states

Results of a self-consistent “Augmented Plane Wave” (APW) band-structure calculation are presented for substoichiometric titanium carbide with 25% vacancies on the carbon sublattice sites (TiC_{0 75}) assuming a model structure with ordered vacancies Comparison with an earlier APW study on stoichiometric TiC reveals that the carbon vacancies induce two pronounced peaks in the density of states (DOS), 0.4 eV below and 0.8 eV above the Fermi energy E_γ, thus forming electronic states in a region where the DOS for stoichiometric TiC exhibits a minimum So-called “vacancy states” with an important amount of charge on the vacancy site are found to be derived from Ti 3d states extending into the vacancy muffin tin sphere An angular momentum decomposition with respect to the center of the vacancy muffin tin sphere shows that the s character predominates for the occupied and the p character for the unoccupied “vacancy states” The theoretical findings explain features near E_γ, observed in recently published X-ray emission spectra Furthermore, we find a slight increase of electronic charge in the carbon muffin tin spheres as compared with stoichiometnc TiC.     

A critical consideration of magnetism and composition of (bcc) Cu precipitates in (bcc) Fe

Atom probe and small-angle neutron scattering (SANS) measurements were carried out in order to investigate the chemical composition of (bcc) Cu precipitates in a (bcc) Fe matrix. The ratio of nuclear and magnetic integrated intensities (R-value) found by SANS is compared to a theoretical model which is based on the chemical composition obtained from the atom probe data. Furthermore, density functional theory calculations were performed to derive the magnetic moment per atom and the lattice parameters of the Cu alloys modeled in terms of supercells. The calculated and measured R-values agree rather well suggesting that Fe atoms are incorporated in the Cu precipitates up to concentrations of about 50 at.%.     

Rotational analysis of the B2Σ+ → X2Σ+ system of the aluminum monoxide radical,AlO

Twenty-five bands of the B²Σ → X²Σ system of AlO with 0 ≤ v′ ≤ 9 and 0 ≤ v″ ≤ 6 have been photographed at high resolution. The measured positions of the assigned lines of each band have been fitted by least-squares to obtain estimates of the constants (B′, D′, B″, D″), the band origin, and Δγ_v′,v″, which is the difference of the upper and lower state spin-doubling constants (γ′_v and γ″_v). The parameters from individual bands have been merged to single-valued estimates, as well as to polynomial representations in ($\text{v +}\text{1}\text{2}$). Although the spin-doubling constants are not found absolutely for either state, their vibrational dependences are well determined. The data are employed in the computation of RKR potential energy curves and an array of Franck-Condon factors and r-centroids.     

Transformation processes in deformed Al-30 wt.% Zn alloy containing metastable precipitates

The Al-30wt.%Zn alloy containing metastable α′_R or α′ precipitates was cold rolled to investigate the effect of plastic deformation on transformation processes during the subsequent ageing at 200 °C. Transmission electron microscopy and X-ray diffraction studies proved that the deformation leads to the rapid decomposition of deformed α′_R and α′ precipitates and enhances also the decomposition of α′ precipitates formed from α′_R to α′ transformation. The deformation does not, however, change the growth rate of α′ particles. It leads, therefore, to the decrease of critical sizes of α′ particles for the α′ to β transformation. The increasing degree of deformation enhances the density of nucleation sites for the β formation on α/α′ interfaces and leads to the decrease in sizes of stable β precipitates. The acceleration of transformation processes is associated with the partial relaxation of stresses introduced by the applied deformation.     

Calculation of spectroscopic constants and radiative parameters for the B 1Π-X 1Σ+ electronic transitions of NaK,NaRb, and NaCs molecules

The vibrational, rotational, and centrifugal spectroscopic constants and the radiative parameters (the Einstein coefficients, oscillator strengths, Frank-Condon factors, r _v′v″ centroids, and wavenumbers of rotational lines) of electronic-vibrational-rotational transitions in the systems of bands B ¹Π -X ¹Σ⁺ of NaK (0 ≤ v′ ? 14, 0 ≤ v″ ≤ 52, j = 0, 30, 50, 70, 80, and 100), NaRb (0 ≤ v′ ≤ 12, 0 ≤ v″ ≤ 51, j = 0, 20, 30, 50, 70, 90, 100, and 120), and NaCs (0 ≤ v′ ≤ 10, 0 ≤ v″ ≤ 44, j = 0, 30, 50, 70, 90, 100, and 120) molecules, as well as the radiative lifetimes of excited electronic states, are calculated. Calculations are performed based on semiempirical potential curves constructed in this work. The calculated spectroscopic constants and the radiative lifetimes are compared with experimental values.     

Atom-probe investigations of fine-scale features in intermetallics

Intermetallics have been studied by means of Atom Probe Field Ion Microscopy. Atom-Probe techniques have been used to determine the phase composition and to study the role and the influence of additional elements. The use of the Tomographic Atom Probe makes it possible to map out the distribution of chemical species in a small volume of the material at a near atomic scale. This has been particularly used in order to study segregation of additional elements at interfaces or planar and linear defects in TiAl base and FeAl base alloys.     

Ni/Ni3Al interface: A density functional theory study

The optimal geometries, mechanical and thermal properties, and electronic structures of the three low index (0 0 1), (1 1 0), (1 1 1) Ni/Ni₃Al thin film were studied using first principle calculations. Simulated results indicated that Ni and Al atoms in γ^′ phase preferred to place in the hollow site of Ni atoms in γ phase. In hollow site models, electronic states affected by interface localize within 2 atomic layers. While the top site model, electronic states localize within 3 atomic layers. It is also found that hollow site (1 1 0) interface has the best mechanical properties. Hollow site (0 0 1) interface is the most easily formed interface, which has the best thermodynamic properties.     

Stark spectroscopy with the CO laser: The ν2 fundamental bands of trans- and cis-nitrous acid,HNO2, in the 6-μm region

The ν₂ fundamental bands of trans- and cis-HNO₂ have been studied by the technique of intracavity CO laser Stark spectroscopy. Excited-state rotational constants were determined, and the ν₂-band origins were found to be 1699.760 cm^?1 for the trans isomer and 1640.517 cm^?1 for the cis isomer. The total dipole moments for the ground and excited (v₂ = 1) vibrational states were found to be μ″ = 1.930 D and μ″ = 1.852 D for trans-HNO₂, and μ″ = 1.428 D and μ″ = 1.441 D for cis-HNO₂.     

Microstructural studies of nanocrystalline α-alumina powder produced from Al13-cluster

Nanocrystalline alumina powder was produced from calcinations of Al₁₃-oxalate precipitates at 1100 °C. A nearly normal distribution of agglomerated alumina powder was obtained with an average particle size of about 1 μm. XRD measurement confirmed that the alumina produced was of high purity and crystalline α-phase. Microstructural features of both the precipitates and alumina obtained were studied using the small angle neutron scattering (SANS) technique. SANS examinations show the formation of microstructures in the alumina powder of mass fractals type with dimension of ∼2.8 indicative of low intra-granular porosity.     

Resolution of the discrepancies concerning the optical and microwave values for B0 and D0 of the X 3Σg− state of O2

The discrepancies concerning the optical and microwave values of B₀ and D₀ for the X${}^3\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ state of O₂ have been removed by a nonlinear least-squares fit to all of the lines of the O₂, $\text{b}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}\text{-X}{}^3\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ Red Atmospheric bands recorded by Babcock and Herzberg (Astrophys. J., 108, 167, 1948). The resulting values for B₀″ and D₀″ are in excellent agreement with the Raman and microwave values. Improved values are determined for B₁″, D₁″, γ₁″ (spin-rotation), and ?₁″ (spin-spin). Both γ_v″ and ?_v″ increase in magnitude from v″ = 0 to v″ = 1. Improved Dunham Y_i0 and Y_i1 expansion coefficients are determined for the $\text{b}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ state, from which the Rydberg-Klein-Rees potential is constructed.     

Quantitative analysis of fine nano-sized precipitates in low-carbon steels by small angle neutron scattering

The small angle neutron scattering (SANS) technique was used to determine the nano-sized precipitates in interstitial free (IF) and low-carbon (LC) steels with a hot-rolling temperature. The real-space direct model fitting method was applied to quantitatively analyze the SANS data. The magnetic and chemical properties of precipitates in the samples were also investigated by separation and comparison of nuclear and magnetic SANS scattering data. The size distribution of precipitates in the IF steel is in good agreement with the microstructure observation using transmission electron microscopy. The results revealed that the IF steel had two types of non-magnetic precipitates, Ti₄C₂S₂ and TiC, with the average size of about 30 nm in diameter and little difference in chemical composition. In case of commercial LC steel, the fine and large precipitates are identified as MnS and Fe₃C, respectively. The average size of spherical MnS precipitates was about 4.8 nm in radius and the distribution is isotropic. It is likely that the LC steels have almost the same composition and a similar size as precipitates such as MnS and Fe₃C with different finishing delivery temperatures. Interestingly, the average size and volume fraction of fine precipitates showed no significantly changes under the different finishing delivery temperatures.     

Temperature dependence of N2-broadened halfwidths of ozone

The temperature dependence of N₂-broadened halfwidths of ozone has been studied over a temperature range of 200–500 K. Assuming the form $\text{γ}\text{(T) =}\text{γ}\text{(T}{}_0\text{)(}\text{T}{}_0\text{T}\text{)}{}^{\mathrm{n}}$, the exponent n has been determined from QFT-ID calculations for 126 ro-vibrational transitions of ozone selected to consider a wide range of the rotational quantum number J″ (1 to 35), the full manifold of K″_a for particular J″, values and transitions important to stratospheric studies. The results give an average temperature exponent of n = 0.77 for nitrogen-broadening. The temperature exponents are transition dependent but the fluctuation about the average value is small (±6%). The value on n as a function of J″ and K″_a is investigated. Comparison of the present results with experiment and other theoretical calculations shows good agreement. Based on the results an average temperature exponent for air-broadening of n = 0.76 is suggested.     

Laser-induced fluorescence and microwave-optical double-resonance study of the B1Σ+-X1Σ+ system of magnesium monoxide

Doppler-limited, laser-induced fluorescence spectra on the B¹Σ⁺-X¹Σ⁺ (v′ = v″ = 0 and 1) system of MgO have been obtained. The results of the optical analysis were merged with our microwave-optical double-resonance measurements to produce the following set of spectroscopic parameters for the B and X states, where the units are in cm^?1, and the uncertainties represent 95% confidence limits: T′_0.0 = 20003.594(2); B′₀ = 0.58004(3); D′₀ = 1.13(2) × 10^?6; B″₀ = 0.57198(3); D″₀ = 1.20(2) × 10⁶; T′_1.1 = 20043.423(2); B′₁ = 0.57528(4); D′₁ = 1.14(11) × 10⁶; B″₁ = 0.56674(4); D″₁ = 1.22(10) × 10⁶.     

3 S 1−3 D 1 mixing and E1 radiative transitions in charmonium

The radiative transitions ψ′→γ+χ _J and χ _J →γ+ψ are studied in the quark model with the ψ and ψ′ interpreted conventionally as³ S ₁ \(c\bar c\) states and the χ _J as³ P _J \(c\bar c\) states. In particular, the effect of³ S ₁?³ D ₁ mixing on the decay widths is calculated. The photon angular distributions in these decays are also studied and are found to be a more sensitive test of³ D ₁ admixtures in the Ψ states. The³ D ₁ content of the Ψ is found to be large but the estimate is very sensitive to the photon angular distributions. More precise measurements could help to explain the large ψ″ leptonic width.     

Studies of labile molecules with a tunable dye laser: Laser excitation spectrum of BrF (B3Π(0+)-X1Σ+)

The B³Π(0⁺) ← X¹Σ⁺ absorption spectrum of BrF (4850–5200 Å) has been observed by the technique of laser emission spectroscopy. Fluorescence was excited by a pulsed, scannable dye laser with a 0.1 Å bandwidth. Rotational analysis has been carried out for six bands of the v″ = 0 progression (8 ≥ v′ ≥ 3) of ⁷⁹BrF and ⁸¹BrF. Rotational constants for the B³Π(0⁺) state are reported for the first time. RKR potential energy curves for both states, and an array of Franck-Condon factors and r-centroids for the transition, have been calculated. Bands with v′ > 8 were not observed in fluorescence owing to the onset of predissociation near J′ = 28 of the v′ = 8 level. An upper limit for the ground state dissociation energy is D₀″ (BrF, X¹Σ⁺) ≤ 20 880 cm^?1.     

Laser Stark and laser-microwave double-resonance spectroscopy of the ν2 band of CD3I

The ν₂ fundamental band of CD₃I was investigated by means of the laser Stark spectroscopy using a 10.6 μm CO₂ laser and an N₂O laser as infrared radiation sources. The assignment was established for about 150 Stakr resonances. Laser-microwave double resonance was used to confirm the assignment. A least-squares analysis of the Stark spectrum gave the molecular constants: μ″ = 1.6504 ± 0.0004 D; μ′ = 1.6479 ± 0.0005 D; ν₀ = 28 461 093.8 ± 3.6 MHz; A′ - A″ = 234.0 ± 1.1 MHz; D_K′ - D_K″ = 0.121 ± 0.085 MHz. The uncertainties are 2.5 times the standard deviations. The single and the double primes refer to the ν₂ and the ground vibrational states, respectively.     

Rotational study and hyperfine effects of the (0,0) band of the B2Σ-X2Σ system of ScS

Rotational analysis of the (0,0) band of the B²Σ-X²Σ transition of ScS is reported. Spectrographic illustration of a hyperfine coupling transition in the ground state is demonstrated for the first time. This enables an order of magnitude to be obtained for γ″ (～0.003 cm^?1). The results for the other constants were: X state: B″ = 0.1971 cm^?1, D″ = 5 × 10^?8cm^?1, 4b = 0.23 cm^?1 (equal to that for ScO within the limits of measurement uncertainty); B state: B′ = 0.1853 cm^?1, D′ = 6 × 10^?8cm^?1, γ′ = ?0.0594 cm^?1, which can be compared with p_A²Π = 0.060 cm^?1. It was found that the two excited states A²Π and B²Σ constitute an excellent example of pure precession (p_pp = 0.058 cm^?1, and this enables the vibrational levels of A²Π to be numbered.