Subject index for volume 100

The ν₂ fundamental band of HNCO has been observed for the first time under a resolution of 0.015 cm^?1. The band origin for this NCO antisymmetric stretching vibration is found to be at 2268.893 cm^?1, rather distant from the previously reported value of 2274 cm^?1. Nineteen subbands have been analyzed and term values for both ground and ν₂ states with K up to 4 have been obtained. Effective rotational constants B and centrifugal distortion constants D and H have also been determined. Interactions are observed with 2ν₄ + ν₅ and ν₃ + ν₄. Large perturbations are observed for K = 0 and K = 1 levels of ν₂. Transitions are also seen for three other vibrations, ν₄ + ν₅ + ν₆, ν₃ + ν₆, and 2ν₄ + ν₆.     

Reductive-annealing-induced changes in Mo valence states on the surfaces of MoO3 single crystals and their high temperature transport

Reduction of MoO₃ in extreme reducing condition is a way to achieve Mo metal. However, effect of less extreme reductive-annealing, where it allows to keep the crystal structure, on physical and chemical properties of MoO₃ has not been well-studied. In this work, we studied the evolution of Mo valence state during reductive annealing and its effect on high temperature transport. We found the formation of oxygen vacancies on surface of MoO₃ single crystals at the low temperature, which is evidenced by increase of Mo⁵⁺ and color change. In addition, formation of Mo⁴⁺ was at the elevated temperature. For understanding the relation between bulk conductivity and Mo valence state, real-time impedance spectroscopy is employed. Use of two different gases makes it possible to distinguish impedance responses of MoO₃ from those of reduced MoO_3-x. Also, from time-dependent impedance measurements, we observed the evolution of transport behaviour by evolution of Mo valence state.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.     

Reaction of molecular hydrogen with the 100 face of MoO3: I. Kinetics in the low pressure range (10−8–10−6 Torr) in the presence of platinum particles

Three successive processes are observed when the 100 face of a MoO₃ single crystal covered with a specific density of platinum particles of known diameter is exposed to molecular hydrogen in a pressure (P) domain between 10^?8 and 10^?6 Torr. During the first step, called the activation step, the rate process is a function of the surface area of the Pt particles and it is slightly thermally activated. During this activation step, H₂ dissociatively chemisorbed on the platinum surface and the hydrogen atoms are inserted into the MoO₃ surface layers. The inserted atom is partially ionized, the electrons given to the lattice reducing Mo⁶⁺ into Mo⁵⁺ and Mo⁴⁺. The rate of hydrogen insertion (V_a) in the activation step increases about linearly with time. The activation step is followed by a stationary step where V is independent of the extent of the Pt surface, V = 0.7Z(1?X), where Z is the number of collisions between H₂ and the MoO₃ surface and X the electronically reduced fraction of the surface area. $\text{X =}\text{a}\text{P}\text{(1 + a}\text{P}\text{)}$, where a is a function of the temperature only. In the stationary step, the platinum particles do not play any role and molecular hydrogen is dissociatively chemisorbed on the MoO₃ surface. The stationary step is followed by a deceleration step. The slowing down of the reaction rate is due to the formation of fractures within the crystal. During all these three steps, the surface is self-cleaning, since protons diffuse into the bulk. The final product of the insertion process would be H_1.6MoO₃, the properties of which have been studied in detail elsewhere. The model which is summarized above is very different from that which would result from the classical views on the so-called hydrogen spillover process since the Pt surface producing the H atoms spilling over the surface would operate only during the activation step.     

The IR and Raman spectra of Tb0.2Dy0.9Gd0.9(MoO4)3

The IR and Raman spectra of the ternary molybdate Tb_0.2Dy_0.9Gd_0.9(MoO₄)₃ have been recorded and analysed on the basis of the vibrations of MoO²⁻₄ ions. The splitting of the non-degenerate Mo—O symmetric stretching mode due to the vibrational interaction between neighbouring ions is observed. The large splitting observed for the v₃(F₂) mode is probably due to the large number of MoO²⁻₄ ions and strong interlayer coupling present in the unit cell.     

Structure of excited states in100Mo and102Mo from spectroscopy using18O induced reactions

The lifetimes have been determined for the 2⁺, 0^+～ and 4⁺ states in¹⁰⁰Mo and¹⁰²Mo using the recoil-distance Doppler-shift method. The states have been excited in¹⁰⁰Mo by Coulomb excitation and in¹⁰²Mo by the two-neutron transfer reaction induced by¹⁸O ions on a¹⁰⁰Mo target. The study of the excitation function for the elastic and inelastic scattering on the ground and first excited 2⁺ state in¹⁰⁰Mo at beam energies between 20 and 61 MeV shows that 40 MeV is the highest incident energy for pure Coulomb excitation. Above this energy nuclear absorption sets in and nuclear scattering contributes to the excitation of the 2⁺ state of¹⁰⁰Mo. From the lifetimes of the 2⁺ and 4⁺ states deformation parameters of ¦β¦= 0.21 and ¦β¦=0.31 for¹⁰⁰Mo and¹⁰²Mo respectively were deduced. The 0^+′ levels are not shape isomeric states, as suggested earlier, but they decay by enhancedE2 transitions to the first 2⁺ states. From a comparison with similar states in other transitional nuclei it is suggested that they are band heads forβ vibrational bands.     

The ratio of the quadrupole moments of the isotopes95Mo and97Mo

The spin-lattice relaxation timesT ₁ of the NMR signals of⁹⁵Mo and⁹⁷Mo in aqueous K₂MoO₄ solutions were determined by the inversion recovery technique. To separate the relaxation rates due to electric quadrupole interaction and due to magnetic dipole interaction, pure H₂O and mixtures of H₂O and D₂O were used as solvent. No dependence of the ratio of the relaxation ratesT ₁(⁹⁵Mo)/T ₁(⁹⁷Mo) on the composition of the solvent was to be detected, i.e. the relaxation due to magnetic dipole interaction may be neglected. From the ratio of the relaxation rates the absolute value of the ratio of the quadrupole moments of the molybdenum isotopes was evaluated: ¦Q(⁹⁷Mo)/Q(⁹⁵Mo)¦ = 11.4 ±0.3.     

Laser Stark spectroscopy of methyl cyanide in the 10-μm region: Analysis of the ν4 and ν7 bands,and the ν7, 3ν81 interaction

About 550 Stark tuned resonances of the ν₄ and ν₇ vibration-rotation bands of CH₃CN were measured using ¹²CO₂, ¹³CO₂, and N₂O lasers. These data are combined with 26 microwave measurements and fitted to a model which includes l-type doubling in ν₇, ν₄-ν₇ Coriolis coupling, and ν₇-³ν₈¹ Coriolis and Fermi couplings. The infrared and microwave data can be reproduced with standard deviations of 7 MHz and 40 kHz, respectively. The many vibration-rotation parameters and the dipole moments are determined with great accuracy. A complete list of derived parameters is given in Table I.     

Measurements of spatially resolved electron number densities and modes temperatures using optical emission spectroscopy of atmospheric pressure microplasma jet

The electrical gas discharge parameters of direct-current non-thermal microplasma jet in Ar-2%H₂ flow at open atmospheric air was investigated by using spatially resolved optical emission spectroscopy (OES). The jet was confined from microhollow of tungsten-carbide (～500 μm inner diameter) to a molybdenum foil. Despite its small volume, the atmospheric pressure microplasma jet provides a range of power densities, from low to ～10¹² W m^?3 generated either in rare gases or in molecular gases. A high resolution spectrometer (Jobin-Yvon, Czerny-Turner model THR1000, resolution of 0.001 nm, with focal length of 1.0 m and numerical aperture of 0.13 ? f/7.5) was used to allow registration of OH (A ²Σ⁺, ν = 0 → X ²Π, ν′ = 0) rotational bands at 306.357 nm, Ar I 603.213 nm line and N₂ (C ³Π _u , ν = 0 → B ³Π _g , ν′ = 0) second positive system with the band head at 337.13 nm in order to estimate the rotational temperature from the cathode sheath of the plasma jet to the anode. For currents ranging from 20 to 100 mA and for a particular excited levels, the excitation temperature was measured in the negative glow region either from a Boltzmann plot of Ar I 4p–4s and 5p–4s transitions of excited argon or using the Mo I (from 440 to 450 nm) two-lines method of excited Mo atoms sputtered from the cathode surface, giving 24 000 K (100 mA at 100 μm) and 7000 K (20 mA at 500 μm from the cathode). From the N₂ (C ³Π _u , ν = 0 → B ³Π _g , ν′ = 0) rotational transition the rotational temperature along the positive column was estimated. The vibrational temperature of the bulk plasma (1400 to 4500 K) was estimated for a current varying from 20 to 120 mA using the N₂ second positive system with Δν = ?2. Using the broadening of H _β Balmer line it was possible to estimate the electron number density of the negative glow (10¹⁴ to 10¹⁵ cm^?3) as a function of the current.     

Excited states of100Tc from100Mo(p,nγ)100Tc reaction and the parabolic rule

γ-spectra and excitation functions of the¹⁰⁰Mo(p, nγ)¹⁰⁰Tc reaction were measured in the 1.2–3.6 MeV proton energy range by using thick, enriched targets, Ge(Li) and low energy photon (hyperpure Ge) spectrometers. These detectors were used inγγ-coincidence experiments, too. Conversion electron spectrum measurements were performed by means of a superconducting magnet transporter Si(Li) spectrometer (SMS) atE _p =4 MeV and multipolarities of some transitions have been determined. Based on the experimental results a level scheme of¹⁰⁰Tc has been constructed. Level energies of¹⁰⁰Tc were calculated on the basis of the parabolic rule, derived from the cluster-vibration model.     

Extended line assignments for the ν3 + ν4 band of 12CH4

The ν₃ + ν₄ absorption band of ¹²CH₄ at 2.3 μm has been re-examined at 0.01-cm^?1 resolution with a Fourier transform spectrometer in order to extend and review the line assignments of Bobin and Guelachvili. More than 300 new or revised excited-state energy levels have been determined by means of combination differences in ν₃ + ν₄ and corroborating lines in the spectrum of ν₃ + ν₄ ? ν₄ at 3.3 μm.     

Epitaxial MoOx nanostructures on TiO2(1 1 0) obtained using thermal decomposition of Mo(CO)6

Stoichiometric and highly-defective TiO₂(1 1 0) surfaces (called as yellow and blue, respectively) were exposed to Mo(CO)₆ vapours in UHV and in a reactive O₂ atmosphere. In the case of yellow-TiO₂, an O₂ reactive atmosphere was necessary to obtain the Mo(CO)₆ decomposition at 450 °C with deposition of MoO_x nanostructures where, according to core level photoemission data, the Mo⁺⁴ state is predominant. In the case of blue-TiO₂ it was possible to obtain Mo deposition both in UHV and in an O₂ atmosphere. A high dose of Mo(CO)₆ in UHV on blue-TiO₂ allowed the deposition of a thick metallic Mo layer. An air treatment of this sample at 580 °C led to the elimination of Mo as MoO₃ and to the formation of a transformed layer of stoichiometry of Ti_(1−x)Mo_xO₂ (where x is close to 0.1) which, according to photoelectron diffraction data, can be described as a substitutional near-surface alloy, where Mo⁺⁴ ions are embedded into the titania lattice. This embedding procedure results in a stabilization of the Mo⁺⁴ ions, which are capable to survive to air exposure for a rather long period of time. After exposure of the blue-TiO₂(1 1 0) substrate to Mo(CO)₆ vapours at 450 °C in an O₂ atmosphere it was possible to obtain a MoO₂ epitaxial ultrathin layer, whose photoelectron diffraction data demonstrate that is pseudomorphic to the substrate.     

Results on two-, three-, and four-body events from the100Mo+100Mo and120Sn+120Sn collisions aroundE/A=20 MeV

Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions¹⁰⁰Mo+¹⁰⁰Mo atE/A =18.7, 23.7 MeV and¹²⁰Sn+¹²⁰Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP ₃ andP ₄ of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP ₃ andP ₄ curves at high energy losses. Small deviations of theP ₃ andP ₄ curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.     

Laser Stark and laser microwave double-resonance spectroscopy of deuterated fluoroacetylene with the CO2 laser

The CO₂ laser Stark spectrum of deuterated fluoroacetylene was identified with the aid of the double-resonance technique for the ν₃, ν₃ + ν₅ ? ν₅, ν₃ + ν₄ ? ν₄, ν₃ + 2ν₅ ? 2ν₅, and ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅ vibrational bands. Laser microwave double-resonance signals were observed in the presence of the Stark field. From the analysis of the double-resonance signals precise values of the dipole moment were obtained for 10 vibrational states, in Debye, with the uncertainties in parentheses: ground, 0.73292(22); ν₅, 0.75656(17); ν₄, 0.68412(24); 2ν₅(Σ⁺), 0.78063(21); ν₄ + ν₅(Σ⁺ or Σ^?), 0.70698(19); ν₃, 0.75772(30); ν₃ + ν₅, 0.78270(18); ν₃ + ν₄, 0.70822(17); ν₃ + 2ν₅(Σ⁺), 0.80808(25); ν₃ + ν₄ + ν₅(Σ⁺ or Σ^?), 0.73329(17). The band origins were determined (in cm^?1); ν₃, 1045.9242(8); ν₃ + ν₅ ? ν₅, 1049.6441(8); ν₃ + ν₄ ? ν₄, 1047.8700(8); ν₃ + 2ν₅ ? 2ν₅(Σ⁺-Σ⁺), 1053.0374(8); ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅(Σ⁺?Σ⁺ or Σ^??Σ^?), 1051.5040(8).     

Line strengths of the ν3 - ν4 band of methane

Strengths of 413 lines of the ν₃ - ν₄ band of methane from 1568 to 1932 cm^?1 have been measured with 2 to 4% accuracies using spectra recorded at 0.011 cm^?1 (unapodized) resolution. Transition strengths up to J₃ = 14 have been fitted with a standard deviation of 4% using a four-term, first-order expansion of the dipole moment. A band strength of 0.050(2) cm^?2 atm^?1 at 296 K is reported for ν₃ - ν₄ of ¹²CH₄. Estimated band strengths of ν₁ - ν₄, ν₃ - ν₂, ν₃ + ν₄, ν₁ + ν₄, and ν₂ + ν₃ are also given.     

Influence of photoexcitation on the EPR spectra of Mo5+ in Li2Zn2(MoO4)3: Ce3+,Cu2+ crystals annealed in a CO2 atmosphere

The influence of recovery annealing in a CO₂ atmosphere at 700°C on the properties of Li₂Zn₂(MoO₄)₃ crystals doped with cerium and copper ions has been studied. The EPR investigation of Li₂Zn₂(MoO₄)₃ crystals annealed in a CO₂ atmosphere has revealed that the annealing leads to the formation of oxygen vacancies in positions adjacent to the oxygen octahedron of lithium, M3, and the oxygen tetrahedron of molybdenum, Mo1. In this case, the charge state of molybdenum becomes Mo⁵⁺ and appears in the EPR spectra in the form of one magnetically nonequivalent position. The analysis of the angular dependence of the EPR spectrum of Mo⁵⁺ made it possible to calculate the spectral parameters g _∥ = 1.862, g _⊥ = 1.933, A _∥ = 71.8 G, and A _⊥ = 34.1 G. The cross relaxation on the hyperfine structure from the molybdenum isotope ⁹⁷Mo is found in the EPR spectra. The photoexcitation of Li₂Zn₂(MoO₄)₃ crystal doped with cerium ions leads to the saturation of the EPR spectrum of Mo⁵⁺ and to the formation of the hyperfine structure from one lithium ion with a hyperfine structure constant of 14 G. For Li₂Zn₂(MoO₄)₃ crystals doped with copper ions, a very weak EPR spectrum of Mo⁵⁺ is observed in the initial crystals. As a result of the photoexcitation, an increase in the intensity of this spectrum by an order of magnitude and manifestation of the EPR spectrum of Cu²⁺ ions take place. It is assumed that such a behavior of the EPR spectra of molybdenum ions in Li₂Zn₂(MoO₄)₃ crystals doped with cerium and copper ions under photoexcitation is caused by different positions of the energy levels of cerium and copper ions with respect to the energy level of the molybdenum ion.     

X-Ray photoelectron and mössbauer spectroscopy studies on molybdenum-bearing ferrite

The X-ray photoelectron spectra of Mo 3d electrons (232.4–232.9 and 229.4–229.6 eV) for Mo-bearing ferrites have suggested that molybdenum ions are in the 4+ valence state on the lattice points in the spinel structure. The XPS data for Mo 3d and Fe 2p electrons combined with the Mössbauer data at room temperature suggest that Fe₂MoO₄ takes a valence state (Fe²⁺)_tet[Fe²⁺Mo⁴⁺]_octO₄.     

Analysis of the ν1 and ν2 + ν4 bands of 12CH4

Line assignments, positions, strengths, and experimentally determined upper states are reported for the ν₁ and ν₂ + ν₄ infrared bands of ¹²CH₄. The bands have been analyzed using infrared spectra recorded with different optical densities and temperatures at 0.02- and 0.01-cm^?1 resolution using a four-passed grating spectrometer at Florida State University and a Fourier transform spectrometer at Kitt Peak National Observatory. Both ν₁ and ν₂ + ν₄ lines are assigned through J′ = 14. For J′ ≥ 10, the upper state of the vibrationally infrared inactive ν₁ band interacts strongly with ν₂ + ν₄ and is observed in the infrared spectrum with line strengths on the order of 10^?3 cm^?2 atm^?1. The upper-state energies and transition intensities are calculated from the molecular constants and transition moment matrix elements obtained through a simultaneous analysis of ν₁, ν₃, ν₂ + ν₄, 2ν₄, and 2ν₂.     

Double beta decay of 100Mo

Two-neutrino double beta decay of ¹⁰⁰Mo with half-life T _1/2=[7.2±0.9(stat)± 1.8(syst)]×10¹⁸ yr was detected using a liquid argon ionization chamber. With a C.L. of 68% (90%), the bounds on neutrinoless decay and decay with majoron emission were found to be 8.4(4.9)×10²¹ and 4.1(3.2)×10²⁰ yr, respectively. An analysis of all available results provides the average “world” value T _1/2=(8.0±0.7)×10¹⁸ yr for the two-neutrino decay of ¹⁰⁰Mo, and the corresponding nuclear matrix element is M _GT=0.118±0.005.