Radiative width of the first T = 2 state in 8Be

The lowest T = 2 state (J^π = 0⁺) in ⁸Be was observed as a resonance at E_d = 6962.8 ± 3.0 keV (E_X = 27495.8 ± 2.4 keV, λ_c.m. = 5.5 ± 2.0 keV) in the ⁶Li(d, γ)⁸Be reaction. The resonant capture yield to the 17.6 MeV J^π = 1⁺, T = 1 state gives λ_γ = 23 ± 4 eV (1.14 ± 0.20 W.u.), in good agreement with the intermediate coupling model.     

Formation of short-period multilayer W/B4C compositions

The quantitative characteristics of the interlayer interaction in multilayer W/B₄C periodic compositions produced by magnetron sputtering are studied by small-angle X-ray diffraction using CuK _?? radiation and by electron microscopy of transverse cuts. It is found that approximately 0.85 nm of the tungsten layer thickness is consumed for the formation of mixed zones at layer boundaries. The mixed layers have a density of 13.4 ± 0.7 g/cm³ and contain tungsten in a bound chemical state. The effect of these mixed zones on the X-ray reflectivity of multilayer W/B₄C compositions is estimated. A method is proposed to determine the layer thickness at a small number of peaks in an X-ray diffraction pattern.     

Microwave determination of the conformation and dipole moment of 1,3-difluoroacetone

The microwave spectra of the ground state and several low-lying vibrational modes of 1,3-difluoroacetone have been assigned and analyzed. The assigned form has a molecular conformation in which one fluorine atom lies cis and the other trans to the oxygen atom. The rotational constants of the ground state species were determined using a centrifugal distortion analysis: A = 6024.843 ± 0.006 MHz, B = 2454.414 ± 0.001 MHz, C = 1783.897 ± 0.001 MHz. The molecular dipole moment components of the ground state species lie along the a and b principal axes with μ_a = 2.38 ± 0.03 D, μ_b = 0.89 ± 0.03 D, and μ_T = 2.54 ± 0.03 D. Comparative intensity measurements with OCS microwave lines indicate that the assigned form constitutes only 20% to 30% of the total gas mixture, the remainder presumably consisting of one or more other conformers, perhaps the gauche-gauche form. The lowest vibrational frequency (82 ± 12 cm^?1) is attributed to the trans-CH₂F torsion, while the next-higher vibrational frequency (127 ± 15 cm^?1) is believed to be the cis-torsion. A low-frequency in-plane bending motion is found at 285 ± 25 cm^?1.     

Investigation of the reaction 2H(n,np) at θn = 0°

The differential cross section of the ²H(n, np) reaction was measured at θ_n = 0°. Because of the applied special geometry the experimental data extend over a large fraction of the phase space, including several final state interaction regions as well as regions far from the dominance of quasi-two-body processes. The experiment was analysed with an exact three-body calculation using s-wave separable potentials (CEE). The analysis of the n-n and n-p final state interaction peaks gave a_nn = ?16.3 ± 1.6 fm for the n-n ¹S₀ scattering length and r_nn = 3.15 ± 0.7 fm for the effective range. Remarkable deviations from the calculated cross sections-were found in regions where no strong final state interaction was present.     

Measurement of the population of the4 P 5/2-state in Ar15+ by cascading processes

The population of the⁴ P _5/2-state in Ar¹⁵⁺-ions by cascading processes was measured. The corrected lifetime is (0.55±0.04) ns and is in very good agreement with the theoretical value of 0.56 ns. At a specific beam energy of 1.4 MeV/u the lifetime of the³ P ₂-state of Ar¹⁶⁺ is not influenced by cascading processes and is (1.44±0.08) ns. The energies of the³ P ₂ →¹ S ₀- and⁴ P _5/2 →² S _1/2-transitions are (3127.2±0.5) and (3090.0±0.7) eV, respectively.     

Molecular binding states on clean and oxidized surfaces: SiO(g) + W(clean) and SiO(g) + W(oxidized)

The interactions between a molecular beam of SiO(g) and a clean and an oxidized tungsten surface were examined in the surface temperature range 600 to 1700 K by mass spectrometrically determined sticking probabilities, by flash desorption mass spectrometry (FDMS) and by Auger electron spectroscopy (AES). The sticking probability, S, of SiO has been determined as a function of coverage and of surface temperature for the clean and the oxidized tungsten surface. Over the temperature range studied and at zero coverage S = 1.0 and 0.88 for the clean and oxidized tungsten surfaces respectively. The results are consistent with both FDMS and AES. For coverage up to one monolayer there is one major adsorption state of SiO on the clean tungsten surface. FDMS shows that T_m = constant (T_m is the surface temperature at which the desorption rate is maximum) and that desorption from this state is described by a simple first order desorption process with activation energy, E_d = 85.3 kcal mole^?1 and pre-exponential factor, ν = 2.1 × 10¹⁴ sec^?1. AES shows that the 92 eV peak characteristic of silicon dominates. In contrast on the oxidized tungsten surface, T_m shifts to higher temperatures with increasing coverage. The data indicate a first order desorption process with a coverage dependent activation energy. At low coverage (θ ? 0.14) there is an adsorption state with E_d = 120 kcal mole^?1 and ν = 7.6 × 10¹⁹, while at θ = 1.0, E_d = 141 kcal mole^?1. This variation is interpreted as due to complex formation on the surface. AES shows that on oxidized tungsten, in contrast to clean tungsten, the dominant peaks occur at 64 and 78 eV, and these peaks are characteristic of higher oxidation states of silicon. Thus, it is concluded that SiO exists in different binding states on clean and oxidized tungsten surfaces.     

High field microscopy of nickel on tungsten

Field emission and field ion microscopy have been used to study the properties of nickel layers adsorbed on tungsten, and the growth of nickel crystallites. The first monolayer of nickel has a maximum density of 0.97 ± 0.05 × 10¹⁹ atoms m^?2 and results in an increase in the work function which can be attributed to the formation of dipoles of moment μ₀ = 1.70 ± 0.08 × 10^?30Cm at zero coverage and polarizability $\text{α = 7.3 ± 0.05}\text{A}\text{?}{}^3$. Nickel desorbs from the tungsten surface with activation energy 4.22 ± 0.01 eV and second layer atoms desorb with activation energy 3.2 ± 0.02 eV. Surface diffusion of second and higher layers over clean tungsten layer is believed to proceed by the “unrolling carpet” mechanism, with activation energy 0.93 ± 0.03 eV in close agreement with measurements of surface self-diffusion of nickel. Nickel does not dissolve appreciably in single-crystal tungsten and we confirm that atomic disordering at the nickel-tungsten interface is confined within a few angstroms of the interface. Well-ordered crystallites can be grown from a central nuclear structure which develops on (110)W. Combination of field ion and field emission techniques indicate that the crystallites adopt the expected growth form, having surfaces comprising large low-index faces, and also serve to confirm that field emission images alone cannot be relied upon to give an indication of crystallite shape. Crystallites invariably form upon an adsorbed layer which is at least one atom thick but may be thicker depending upon conditions of growth. The growth of crystals in situ offers the possibility of generating well-ordered low-index planes of large area which are suitable for further study, but it has yet to be confirmed that they behave as surface planes of bulk nickel.     

Heat capacity and magnetic susceptibility of ReO3

The specific heat and magnetic susceptibility of the transition metal oxide ReO₃ have been measured. The specific heat results give a Debye temperature Θ_D = 460 ± 10 K and an electronic specific heat coefficient γ = 6.45 ± 0.07 cal/mole K² which are in good agreement with similar measurements on the cubic sodium tungsten bronzes. The magnetic susceptibility and the electronic contribution to the specific heat are within a few percent of the corresponding parameters calculated from the free electron model with one electron per unit cell. Our results show that ReO₃ behaves much like a simple metal. No experimental evidence for narrow d-band effects was observed.     

Microwave spectrum and rotational isomerism of 3,3-difluoropropene CHF2CHCH2

The analysis of the microwave spectrum of 3,3-difluoropropene has confirmed the existence of two rotational isomers, cis and gauche. The rotational constants in the ground vibrational state are A = 9126.08 MHz, B = 3722.120 MHz, and C = 2946.598 MHz for the cis form and A = 8901.64 MHz, B = 4192.759 MHz, and C = 3107.718 MHz for the gauche form. The dipole moment and its components along the principal axes of intertia are μ_a = 2.369 ± 0.015 D, μ_c = 0.70 ± 0.03 D, and μ_t = 2.47 ± 0.03 D for the cis form and μ_a = 1.535 ± 0.015 D, μ_b = 0.53 ± 0.04 D, μ_c = 1.36 ± 0.03 D, and μ_t = 2.12 ± 0.05 D for the gauche form. The relative intensity measurement indicates that the cis form is more stable than the gauche form by 260 ± 80 cm^?1. The energy of the first excited state with respect to the ground state was found to be 63 ± 8 cm^?1 for the cis form and 85 ± 10 cm^?1 for the gauche form. Two Fourier coefficients of the potential function restricting the torsion around the CC bond were determined to be V₁ = 266 ± 40 cm^?1 and V₃ = 508 ± 200 cm^?1, using the available data. The potential function thus obtained is compared to a prediction model which is derived assuming additivity of the potential as a function of substitution.     

Measured collisional radiative coefficients of the 4p groups of the argon I and argon II systems

We determine the r¹ (p) coefficients of the argon I 4p ¹P₁ state (2p₂ with Paschen notation) with the λ = 696.5 nm line and of the argon II 4p ²D_{$\text{5}\text{2}$} state with the λ = 488.0 nm line in a highly ionized, low temperature (T_{e = 3?4 eV}), magnetically confined (0.2 T) plasma of a hollow cathode arc with electron densities n_e between 10¹⁹ and 10²⁰ m^?3. The neutral density n₀ is 10¹⁹ m^?3 or less. The r¹ (4p) values are (6 ± 2) × 10^?5 for argon I and (5 ± 2) × 10^?4 for argon II.     

The B(E2↑) and Rtr of 21+ states in90Zr and60Ni

The ground state transition probabilities for the 2₁⁺ states in⁹⁰Zr and⁶⁰Ni as determined by resonance fluorescence and reorientation effect methods are used as constraints to deduce transition densities from inelastic electron scattering data. The (e, e') cross sections for the ⁹⁰Zr, 2₁⁺ state at 2.186 MeV were measured at the Kelvin Laboratory, while for the 2₁⁺ state at 1.333 MeV in⁶⁰Ni, the existing (e, e') data of Yale and Sendai were used. The discrepancy between the model independent (e, e') result of Yale for⁹⁰Zr and the (γ, γ') measurement is explained. The importance of an accurate knowledge of the ground state charge distribution for analysis of (e, e') data is emphasized. For⁹⁰Zr, the B(E2↑) is 674 ± 60 e²· fm⁴ and ^R_tr is 5.74 ± 0.11 fm. For the 1.333 MeV state in⁶⁰Ni, these values are 918 ± 26 e²· fm⁴ and 5.33 ± 0.03 fm respectively.     

Infrared diode-laser spectrum of the CH3CN ν2 band: Analysis of local resonances with ν6±1 + 2ν8±2, ν4 + ν7±1 + ν8±1, ν4 + ν6±1, ν4 + ν7±1, and 2ν70 + ν8±1 states

Fifty-one sections of infrared diode-laser spectra of acetonitrile have been measured in the region from 2283.5 to 2235.7 cm^?1. About 450 transitions belonging to the ν₂ band have been assigned for K ≦ 7 and J ≦ 44. Anomalies found in the rotational structure have been proven to be due to five local resonances. Observed transition frequencies have been fitted by a least-squares method to a model which includes Fermi-type resonances (Δk = 0, Δ? = ± 3n) with ν₆^±1 + 2ν₈^±2 and ν₄ + ν₇^±1 + ν₈^±1 states, x, y-type Coriolis resonances (Δk = ±1, Δ? = ?3n ± 1) with ν₄ + ν₆^±1 and ν₄ + ν₇^±1 + ν₈^±1 states, and a centrifugal-distortion-type resonance (Δk = ±2, Δ? = ?3n ± 2) with a 2ν₇⁰ + ν₈^±1 state. The 11 × 11 dimensional energy matrix has been diagonalized in order to obtain the perturbed energy levels. The standard deviation for the fit is 1.075 × 10^?3 cm^?1. The molecular constants determined are also listed.     

Vibrational satellites in the microwave spectrum of cyclopropylidene methanone: Extension of rigid and semirigid bender calculations to larger molecules

The microwave spectrum of cyclopropylidene methanone (CPM) at room temperature includes a large number of vibrational satellites. It has been possible to assign the spectrum of the ground state and nine additional series of satellites. Assignment to vibrational states with up to four quanta of the low-lying out-of-plane (ν₁₅) and two quanta of the in-plane (ν₂₁) bending modes was made by use of several lines of argument:

• 1.(i) relative intensities of lines of the same vibrational state for determination of the parity;
• 2.(ii) variation of A and B-C with vibrational quantum number in comparison with model calculations for in-plane and out-of-plane bending of the heavy atoms;
• 3.(iii) identification of members of the same vibrational sequence by inspection of quotients of differences of their rotational constants.

We have generalized the bender method of Bunker et al. for numerical application to larger molecules. Resulting formulae are given in the text. The rigid bender model was used to fit the changes in rotational constants of the vibrational satellites of the out-of-plane bending mode to a double minimum potential with a barrier of 38.1 ± 0.8 cm⁻¹ and minima at ±17.0 ± 0.1°. The ground state lies 5 cm⁻¹ below the barrier. The in-plane bend is almost harmonic. Its frequency of 197 cm⁻¹ was determined from an analysis of a Coriolis interaction of the v₁₅ = 3, v₂₁ = 0 state with the v₁₅ = 0, v₂₁ = 1 state. The vibrational-state dependence of the centrifugal distortion constants could be at least qualitatively reproduced in this model. The vibrational satellite shifts are equally well fitted when semirigidity is included as suggested by ab initio 4–31G MO calculations. In this case the barrier is slightly lower and the frequencies of ν₁₅ and ν₂₁ decrease by ca. 20%. On the basis of the experimental data presented here it cannot be decided whether the inclusion of semirigidity is necessary.Because the ground state out-of-plane vibrational wavefunction is practically constant over a wide range of the bending coordinate we term CPM quasisymmetric.     

Measurement of the lifetime of the3 P 2 and4 P 5/2 states in Ar16+ and Ar15+

Promptly decaying levels in Li- and Be-like Ar could be identified in the delayed x-ray and electron spectrum in addition to the four known metastable (1s2s)¹ S ₀, (1s2s)³ S ₁, (1s2p)³ P ₂, and (1s2s2p)⁴ P _5/2 states in He- and Li-like systems. The states having lifetimes of about 10^?14s still contribute to the spectrum observed 10^?9s after the ions have passed a foil. This observation is explained by cascading processes from states of high principal quantum numbern≧14. The measured lifetime of the⁴ P _5/2 state subtracting the contribution of cascades is (0.594±0.016) ns and slightly larger than the theoretically predicted value of 0.563 ns. The³ P ₂ state is depopulated at short distances behind the foil by cascading processes. Its measured lifetime of (1.44±0.08) ns compares to a theoretical value of 1.48 ns.     

The non-mesonic to π− mesonic decay ratio and Λ-neutron stimulation fraction for p-shell hypernuclei

Kinematic analysis of simple hypernuclear production reactions has produced a sample of hypernuclei of _ΛB, _ΛC and _ΛN with negligible background, and a much smaller sample of _ΛBe. The values of the non-mesonic to π^? mesonic ratio Q^? for the above samples are 5.5 ± 0.5 and 4.3 ± 1.1, respectively. A sub-sample of ¹¹_ΛB hypernuclei was separated on the basis of production via an excited state of _Λ¹²C, giving Q^? = 4.8 ± 1.1 for _Λ¹¹B. Assuming the Fermi gas model is applicable to nuclei of mass A ≈ 11, two independent means of analysis of the non-mesonic decays give values for the Λ-neutron stimulation fraction n of 0.41 ± 0.09 and 0.34 ± 0.07 for hypernuclei of charge 5 ≦ Z ≦ 7.     

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.     

Coulomb excitation of the Kπ=16+ rotational band in 178Hf

A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of ¹⁷⁸Hf in the K^πn = 16⁺ isomeric state has been performed at 4.77 MeV/u ²⁰⁸Pb beam energy. The first excited I^π = 17⁺ state has been observed at an excitation energy of 357.4 ± 0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment of Q ₀ = 8.2 ± 1.1 b has been derived from the experimental data within the rigid rotor model.     

Internal rotation and inversion doubling in the microwave spectrum of CH3NHCl

The microwave “a” and “c” type spectra of four isotopic species of CH₃NHCl in the ground state and of CH₃NHCl³⁵ and CH₃NDCl³⁵ in the first excited torsional state have been analyzed. From the A-E torsional splittings of the excited state the torsional barrier height has been determined to be V₃ = 3710 ± 46 cal/mole. The “c” type transitions show an inversion doubling of 4.60 ± 0.10 MHz in the ground state and of 5.25 ± 0.10 MHz in the first excited torsional state. Such doublings are independent on the rotational quantum numbers within the experimental errors. The height of the inversion barrier has been roughly evaluated by using the Dennison-Uhlenbeck potential.