Tetravalent vanadium in CaF2 and SrF2 crystals: An EPR study

An EPR study of tetravalent vanadium centers created by room temperature X-irradiation in CaF₂ and SrF₂ is presented. The production efficiency of these centers is enhanced by previous annealing of the samples at 1000 K in air. The symmetry of V⁴⁺ ions is tetragonal and its EPR spectrum can be described by an axial spin Hamiltonian including a Zeeman and hyperfine term with $\text{S =}\text{1}\text{2}$ and $\text{I =}\text{7}\text{2}$ (corresponding to ⁵¹V nuclei). The following values for the spin Hamiltonian parameters are obtained g_∥ = 1.947 ± 0.002, g_⊥ = 1.935 ± 0.005, A_∥ = 500 ± 5 MHz, A_⊥ = 150 ± 10 MHz in the case of SrF₂ and g_∥ = 1.945 ± 0.002, A_∥ = 505 ± 5 MHz and A_⊥ < 200 MHz, in the case of CaF₂. A model for the center including an interstitial O^2? ion is tentatively proposed.     

Valence band parameters of cubic zinc selenide derived from magnetoreflectance of the Γ6 − Γ8 exciton

Magnetoreflectance measurements on the Γ₆ ? Γ₈ free exciton ground state in cubic ZnSe in magnetic fields up to 18 Tesla are reported. The diamagnetic shift rate of the ground state components: $\text{|}\text{3}\text{2}\text{>β}$, $\text{|?}\text{3}\text{2}\text{>α}$, $\text{|}\text{1}\text{2}\text{>β}$ and $\text{|?}\text{1}\text{2}\text{>α}$ yield γ₂ = 0.53 ± 0.07 and an exciton reduced mass μ₀ = 0.117 ± 0.003, corresponding to γ₁ = 2.30 ± 0.45 for m_e¹ = 0.16 m₀. γ₁, γ₂ and an effective hole g-value $\text{κ}\text{tilde}\text{= -0.21}$ yield γ₃ = 0.82 ± 0.16 in the parabolic approximation and in agreement with the observed splitting of the $\text{|?}\text{3}\text{2}\text{>α}$, $\text{|?}\text{1}\text{2}\text{>β}$ states for B ∥ [110]. Taking into account polaron effects we derive bare valence band parameters γ₁^L = 2.71 ± 0.60, γ₂^L = 0.63 ± 0.09 and γ₃^L = 0.97 ± 0.21 from the renormalized parameters γ_i. The present results are considerably smaller than earlier theoretical calculations suggest, however they are in good agreement with a recent detailed analysis of two-photon absorption data for 2P exciton states.     

Determination of A0 for CH335Cl and CH337Cl from the ν4 infrared and Raman bands

The ν₄ infrared and Raman bands of CH₃Cl were analyzed simultaneously. A direct fit yielded a complete set of constants for CH₃³⁵Cl, including A₀ = 5.20530 ± 0.00010 cm^?1 and D_K = (8.85 ± 0.13) × 10^?5cm^?1. For CH₃³⁷Cl an incomplete set of constants was obtained from the infrared band, and A₀ = 5.2182 ± 0.0010 cm^?1 was estimated by curve fitting of the Raman spectrum. The resulting equilibrium structure is $\text{r(}\text{CH) = 1.0854 ± 0.0005}\text{A}\text{?}$, $\text{r(}\text{CCl) = 1.7760 ± 0.0003}\text{A}\text{?}$, and <(HCH) = 110°.35 ± 0°.05.     

Hyperon production in pp interactions at √s = 53 and 62 GeV

Inclusive measurements of Λ⁰, $\text{Λ}$⁰, Ξ^?, Σ(1385)^±) production in the forward direction at the CERN intersecting storage rings are presented. A signal for simulataneous Λ⁰$\text{Λ}$⁰ production is also observed with total $\text{x > 0.6, 2.3 < M}{}_{\mathrm{<mtext>\Lambda </mtext><mtext>\Lambda </mtext>}}\text{< 2.5}\text{GeV}$ and with a cross section of (1.7 ± 0.2) μb.     

Optical detection of cyclotron resonance of electron and holes in CdTe

Cyclotron resonance of electron and holes have been optically detected at 70 GHz and at 1.8 K in n-type CdTe. The bare effective masses, in unit of the free electron mass, are found to be: $\text{m}{}^1\text{= 0.088 ± 0.004}$, $\text{m}{}^1{}_{\mathrm{lh}}\text{= 0.12 ± 0.01}$, $\text{m}{}^1\text{= 0.60 ± for H // <100>}$, and $\text{m}{}^1{}_{\mathrm{e}}\text{= 0.089 0.004}$, $\text{m}{}^1{}_{\mathrm{lh}}\text{= 0.11 ± 0.01}$, $\text{m}{}^1{}_{\mathrm{hh}}\text{= 0.69 ± 0.02}$ for H // <111>. The Luttinger valence band parameters deduced from these measurements are: γ₁ = 5.3 ± 0.5, γ₂ = 1.7 ± 0.3 and γ₃ = 2.0 ± 0.3, in fair agreement with the calculations of Lawaetz.     

Non-cubic Mn2+-centers in BaF2

The EPR spectra of thermally treated BaF₂: Mn samples is reported. After thermal annealing at 900 K a trigonal Mn²⁺ center with g=2.000±0.005, |D|=2725±40MHz, |A|=265±10MHz, $\text{D}\text{A}\text{>0}$, is observed. Annealing at 1200 K produces an orthorhombic Mn²⁺ center with g=2.00±0.01, |D|=2430±40MHz, |E|=570±20MHz, |A|=265±10MHz, $\text{D}\text{A}\text{<0}$. The superhyperfine (SHF) structures due to interactions with the neighbouring fluorines indicates that the trigonal manganese interacts with four fluorines, three of them equivalent. The orthorhombic Mn²⁺ shows interaction with four equivalent fluorine nuclei.     

X and K band ESR study of the Pb Interface centres in thermally oxidized p-type (001)Si wafers at low temperatures and influence of medium-dose As+ ion implantation

Electron spin resonance (ESR) experiments have been carried out at cryogenic temperatures (4.2 ? T ? 35 K) and room temperatures at 9.0 and 20.9 GHz on the P_b0 and P_b1 (commonly referred to as P_b) spin-active defects residing at the Si/SiO₂ interface. The ESR lineshapes were shown to display gaussian characteristics with inhomogeneous line broadenings amounting to 0.7 ± 0.1 and 0.2 ± 0.1 mT at K band for P_b0, and P_b1 respectively, whereas the oscillator strength of both signals followed the paramagnetic law (~ T^?1) down to 4.2 K within experimental error. In general the observed P_b spectrum appeared to have fewer peaks than in other observations, at most displaying two distinguishable lines. Mostly however, only one somewhat broad signal (of measured peak-to-peak linewidth >B_ptp ? 1.5 ± 0.15 mT and g = 2.0058 ± 0.0002 for $\text{\$}\text{?}$B 6 [001] was observed. By fully incorporating ΔB_ptp data for the first time in these observations and using computer simulations, it has been shown that the pervailing experimental spectrum always contains the signals from both kind of centers although mostly these are not separately discernable. Further, it emerged that the actual appearance of the experimental spectra is dirigated by the presence of a distribution of the SiIII unsaturated bond orientations around the ones normally prescribed by the Si crystallinity at the interface. It is found that for both centers this “angle” distribution predominantly occurs vertically with respect to the (001) interface plane. Ion implantation of 10¹⁴ As⁺ cm^?2 at 60 or 80 keV into the oxide layer of the Si/SiO₂ structure is shown to randomize the P_b dangling bond (DB) orientations (resulting in an isotropic g value behavior) but the effect of this is totally eliminated by subsequent annealing at 1000°C in N₂ ambient. It is argued that ESR has become a very sensitive means to study the “purity” of interfacial DB positions with respect to the Si single-crystal prescribed positions and to enable the display of collective fingerprints of the interface defects.     

Spectroscopic analysis of the d1Σ+→a1Σ+ and d1Σ+→b1Π green band systems of XeO

A comprehensive high resolution spectroscopic analysis has been made on the XeO green bands photographed in emission from an RF discharge source. Rotation-vibration constants derived from the analysis of the spectrum of the isotopically enriched species ¹²⁹Xe¹⁶O and ¹²⁹Xe¹⁸O were used to give RKR potential curves for the d¹Σ⁺ and b¹Π states. The bond distances and dissociation energies of the d¹Σ⁺ and b¹Π states were respectively found to be $\text{r}{}_{\mathrm{e}}\text{= 2.852 ± 0.002}\text{A}\text{?}$, D_e = 693 ± 10 cm^?1 and $\text{r}{}_{\mathrm{e}}\text{= 2.548 ± 0.002}\text{A}\text{?}$, D_e = 461 ± 10 cm^?1. For the a¹Σ⁺ state it was not possible to establish a unique vibrational numbering or to construct an RKR potential curve, since observed bands of the d¹Σ⁺→a¹Σ⁺ system involve only high vibrational levels of the a¹Σ⁺ state, which are severely predissociated. The observations are consistent with a fairly deep well, in agreement with the latest ab initio calculations which give a well depth of 0.7 eV.     

The accommodation of trivalent gold in Silver Chloride

Gold-doped silver chloride annealed in a chlorine atmosphere at 300°C is shown to contain precipitates of AgAuCl₄, a compound not previously reported. The substance melts at 265 ± 2°C and has a monoclinic unit cell with $\text{a = 11.124 ± 0.008}\text{A}\text{?}$, $\text{b = 4.105 ± 0.002}\text{A}\text{?}$, $\text{c = 6.539 ± 0.006}\text{A}\text{?}$ and β = 93.11 ± 0.05°. Its optical absorption spectrum is discussed and the method of precipitate formation in silver chloride is described in terms of an internal oxidation type of process.     

New evaluation of muon (g − 2) hadronic anomaly

The hadronic part a_H of the muon g-factor anomaly $\text{a ≡}\text{(g ? 2)}\text{2}$ is evaluated from latest data on σ(e⁺e^? → hadrons). For a p-wave ππ scattering length of a₁ = 0.04±0.005 we calculate a_H = (66±10) × 10^?9, compared to a(experiment) ? a(QED) = (60±29) × 10^?9. Half of the uncertainty on a_H is associated with the energy interval $\text{0.92 <}\text{s}\text{< 2}\text{GeV}$.     

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.     

Isomers in the N = 83 nucleus 149Dy

Energy levels in the N = 83 nucleus ¹⁴⁹Dy were studied by the reaction ¹⁵²Gd(α, 7n) at 106 MeV bombarding energy using in-beam γ-ray spectroscopy methods. The measurements identified three isomers in this nucleus, at 1073 keV (13 ± 3 ns), at 2700±150keV (5 μs < T_{$\text{1}\text{2}$} < 0.5 s), and above 3.5 MeV (50 ± 15 ns). The low-lying isomer is interpreted as i_{$\text{13}\text{2}$}. The configuration $\text{27}\text{2}$^?(πh_{$\text{11}\text{2}$}²)₁₀₊ ×vf_{$\text{7}\text{2}$} is suggested for the state at 2.7 MeV.     

Measurements of elastic scattering in alpha-alpha and alpha-proton collisions at the CERN intersecting storage rings

We measured the elastic scattering of $\text{αα}\text{at}\text{s}\text{= 126}\text{GeV}$ and of αp at $\text{s}\text{= 89}\text{GeV}$. For αα, the differential cross section dσ/dt has a diffractive pattern minima at |t| = 0.10 and 0.38 GeV². At small |t| = 0.05?0.07 GeV², this cross section behaves like exp[(100 ± 10) t]. Extrapolating a fit to the data to the optical point, we obtained for the total cross section α_tot(αα) = 250 ± 50 mb and an integrated elastic cross section σ_e1(αα) = 45 ± mb. Another method of estimating σ_tot(αα), based on measuring the interaction rate, yielded 295 ± 40 mb. For αp, dσ/dt has aminimum at |t| = 0.20 GeV², and for 0.05 < |t| < 0.18 GeV² behaves like exp[(41 ± 2) t]. Extrapolating this slope to |t| = 0, we found σ_tot(αp) = 130 ± 20 and σ_e1(αp) = 20 ± 4mb. Results on pp elastic scattering at $\text{s}\text{= 63}\text{GeV}$ agree with previous ISR experiments.     

Pulsed magnetic field study of Fe2+ in some fluosilicates

Pulsed field experiments up to 450 kOe have been performed on FeSiF_6.6H₂O. We interpret the data: (i) in terms of spin hamiltonian constants: D = 12.3± 0.2 cm^-1 (E = 0.54cm^-1 being known from EPR data); (ii) in terms of axial-crystal-field parameters: $\text{δ}\text{λ}\text{=}\text{orbital trigonal splitting/spin-orbit coupling}\text{= 15 ± 2; λ = -100 ± 7cm}{}^{\mathrm{?1}}$. The magnetic axis is found to deviate from the cristallographie c axis by an angle 1° < θ < 2°. The adiabatic cooling obtained during the pulse is discussed.Similar experiments on Fe_0.15Zn_0.85SiF_6.6H₂O and Fe_0.30Zn_0.70SiF_6.6H₂O single crystals are reported; in both cases we measure $\text{D}\text{g}{}_{\mathrm{\parallel }}\text{= 6.0 ± 0.1cm}{}^{-1}$. Using EPR data, we obtain D = 14.3cm^-1, λ ～ ?75cm^-1, δ ～ 195cm^-1; using Mössbauer data, we obtain D = 15.3cm^-1, λ ～ ?88cm^-1, δ ～ 185cm^-1.     

Measurement of elastic scattering in antiproton-proton collisions at 52.8 GeV centre-of-mass energy

We measured the differential cross section for p?p and pp elastic scattering in the momentum-transfer range 0.01 <|t| < 1.0 GeV² at the CERN Intersecting Storage Rings with center-of-mass energy $\text{s}\text{= 52.8}\text{GeV}$. Fitting the differential cross section with an exponential [Aexp (bt)], we found $\text{b}\text{p}\text{p = 13.92 ± 0.59}\text{GeV}{}^{\mathrm{?2}}$ for |t| < 0.05 GeV², whilst for |t| > 0.09 GeV², $\text{b}\text{p}\text{p = 10.68 ± 0.26}\text{GeV}{}^{\mathrm{?2}}$. Using the optical theorem, we obtained for the total cross section $\text{σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p)= 44.86 ± 0.78}\text{mb}$ and, by integrating the differential cross section, we obtained for the total elastic cross section $\text{σ}{}_{\mathrm{<mtext>el</mtext>}}\text{(}\text{p}\text{p) = 7.89 ± 0.28}\text{mb}$. Calculations of σ_tot combining elastic-rate and total-rate measurements are also given. All of these measurements were also performed for pp scattering at the same energy, and the results for both reactions are compared.     

The microwave spectrum of 14NH3 in the v = 000011 state

The frequencies and assignments of 50 lines in the pure inversion spectrum of ¹⁴NH₃ in the 0001¹ vibrational state are reported in the microwave frequency region 18–53 GHz and in selected regions up to 58 GHz.The J = 0 inversion frequency, K-type doubling constant K, l = 2, ?1 and molecular dipole moment in this state are 32 904.7 ± 2.0 MHz, 1.958 ± 0.040 MHz and 1.459 ± 0.002 D, respectively, where model inadequacies are included in the uncertainties of the first two parameters. The dipole moment measurements for this and the ground state are in excellent agreement with Stark laser measurements. An expression containing the effective l-type doubling constant is obtained from the combination of frequencies $\text{[ν(1, 1, 1) ? ν(1, 1, ?1) ? ν(2, 1, 1) + ν(2, 1, ?1)]}\text{8}\text{= 10 361.894 ± 0.004}\text{MHz}$. A preliminary value for the l-type doubling constant is 10 655 ± 20 MHz.     

Microwave spectrum and structure of cyanamide: Semirigid bender treatment

An extensive study of the microwave spectrum of cyanamide has been undertaken, the analysis being based in part on semirigidbender calculations by the methods of Bunker and Szalay. Inversion lines of NH₂CN, $\text{K}{}_{\mathrm{?1}}\text{= 2}{}^{\mathrm{a}}\text{Q}$ branches and a number of vibrational satellites of the J = 2?1 transition were observed. A two-vibrational-state Hamiltonian was used to fit simultaneously the 0⁺ and 0^? microwave data and yielded rotational constants X, Y, Z, D_J, D_JK, d₁, H_JK as well as the inversion splitting and the μ_yz-connecting matrix element. Vibrational satellite data of seven isotopic species and infrared frequencies of NH₂CN were included in the semirigid bender calculations: The NCN spine is nonlinear by ca. 5° in the equilibrium structure of the molecule. Also, $\text{r}{}_{\mathrm{<mtext>NH</mtext>}}\text{A}\text{?}\text{= 0.9994 + 0.0144?}{}^2$; <HNH/2 = 60.39° ? 0.1134?²; $\text{r}{}_{\mathrm{<mtext>NC</mtext>}}\text{A}\text{?}\text{= 1.3301 + 0.0327?}{}^2$ (? is the inversion angle in rad); $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.1645}\text{A}\text{?}$ fixed. The inclusion of the NC bond flexing was necessary in order to reproduce the observed vibrational satellite patterns of NH₂CN, NHDCN, and ND₂CN. The barrier to inversion of the amino group is 510 ± 6 cm^?1 with minima at ±45.0 ±0.2°. The inversion dipole moment is 0.91 ± 0.02 Debye.     

Microwave spectral study of 2-fluorophenol: cis conformer

The microwave spectra of 2-fluorophenol and its deuterated species have been observed and analyzed in the frequency ranges 12.5–18.0 GHz (KU band) and 21.5–26.0 GHz (K band) in the ground vibrational state at room temperature. For the normal species, the radio frequency-microwave double resonance spectrum has been recorded in the frequency range 30.0–38.0 GHz. Three rotational and five quartic centrifugal distortion constants for the normal species, $\text{A}\text{?}\text{= 3337.86 ± 0.02}$, $\text{B}\text{?}\text{= 2231.92 ± 0.01}$, $\text{C}\text{?}\text{= 1337.52 ± 0.01}$, d_J = (3.5 ± 2.9) × 10^?4, d_JK = (?4.9 ± 1.5) × 10^?3, d_K = (?3.2 ± 1.0) × 10^?3, d_WJ = (?2.0 ± 1.0) × 10^?7, d_WK = (2.6 ± 0.8) × 10^?6 (in MHz), and three rotational constants for the deuterated species, $\text{A}\text{?}\text{= 3324.70 ± 0.03}$, $\text{B}\text{?}\text{= 2177.95 ± 0.03}$, $\text{C}\text{?}\text{= 1315.96 ± 0.03}$ (in MHz), have been obtained. Consideration of the r_s coordinate of the hydroxyl hydrogen atom leads to the assignment of the spectra to the cis conformer of the molecule. An r₀ structure for the cis conformer has been proposed. The nonbonded OH ? F distance is lower by about 0.3 Å than the sum of the van der Waals radii.     

Microwave spectrum of 35ClO in the excited vibrational state and a comment on the centrifugal distortion constant

The $\text{J =}\text{3}\text{2}\text{←}\text{1}\text{2}$ transitions of ³⁵ClO in v = 1 of the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ state were measured and analyzed to obtain the following constants (in megahertz: B = 18 444.86 ± 0.18, p_eff = 669.32 ± 1.08, $\text{a ? (b + c)}\text{2}\text{= 157.05 ± 0.97}$, d = 169.77 ± 0.99, and eqQ = ? 84.78 ± 0.30. The equilibrium bond length is calculated to be 1.56954 ± 0.00005 Å. The transitions in the ground vibrational state, which were reported previously, were reanalyzed by taking into account the matrix elements off diagonal in J of the hyperfine interactions, and led to a refined centrifugal distortion constant, 0.0476 ± 0.0154 MHz. The vibrational frequency increased accordingly to 782 ± 126 cm^?1, which agreed with the value 870 ± 90 cm^?1 obtained from a relative-intensity measurement, and also with other optical spectroscopic data.