Value For D0 Research Articles

What is the Bond Dissociation Energy of the Vanadium Hydride Cation?

Recent electronic state-selected measurements of the reactions of atomic vanadium cations with D2 and CO2 are reanalyzed to properly account for the kinetic energy distribution of the reactant neutrals. The need for this is demonstrated in the present work by comparing the D2 data to that obtained previously in earlier experiments but unpublished. It is shown that the earlier data, which utilized a surface ionization source of V+, and the state-selected data for V+(a5D2) are essentially identical in the threshold regions where they overlap. Differences in the electronic state energies and kinetic energy distributions of V+ in the two experiments are very small and much smaller than the kinetic energy distribution of the neutral reactant, which is identical in both experiments. It is shown that properly accounting for the latter distribution alters the conclusions regarding the threshold energy for the endothermic formation of VD+ such that recent conclusions regarding the bond energy of VD+ are substantially altered and found to reproduce the original bond energy determination. Accounting for all experiments, a revised best value for D0(VH+) is 2.07 ± 0.09 eV [or D0(VD+) = 2.10 ± 0.09 eV]. This conclusion is validated by high-level ab initio calculations. Differences in the new and older data sets for the V+ + D2 reaction at higher energies (above the onset for dissociation of the product ion) are also discussed. The same methodology is then applied to recent studies on the state-selected V+ + CO2 reaction.

Statistical parameter inference of bacterial swimming strategies

We provide a detailed stochastic description of the swimming motion of an E.coli bacterium in two dimension, where we resolve tumble events in time. For this purpose, we set up two Langevin equations for the orientation angle and speed dynamics. Calculating moments, distribution and autocorrelation functions from both Langevin equations and matching them to the same quantities determined from data recorded in experiments, we infer the swimming parameters of E.coli. They are the tumble rate λ, the tumble time r−1, the swimming speed v0, the strength of speed fluctuations σ, the relative height of speed jumps η, the thermal value for the rotational diffusion coefficient D0, and the enhanced rotational diffusivity during tumbling DT. Conditioning the observables on the swimming direction relative to the gradient of a chemoattractant, we infer the chemotaxis strategies of E.coli. We confirm the classical strategy of a lower tumble rate for swimming up the gradient but also a smaller mean tumble angle (angle bias). The latter is realized by shorter tumbles as well as a slower diffusive reorientation. We also find that speed fluctuations are increased by about 30% when swimming up the gradient compared to the reversed direction.

Rheological properties of EP742-ID alloy in the context of Integrated Computational Materials Engineering (ICME). Part 1. Results of experimental research

The article covers rheological properties of the EP742-ID alloy in high-temperature compression tests of cylindrical samples with different ratios of similar initial diameters and heights (d0 /h0). The results of experimental research in the temperature range t = 1000÷1150 °C and initial deformation rates e · 0 = 3·10–2÷3·10–4 s–1 have shown that an increase in compression flow stress with the growth of the d0 /h0 ratio is observed at all temperatures and deformation rates with a linear dependence on the e · 0 value and the d0 /h0 ratio. The method is proposed to recalculate deformation resistance indicators to the set ratio of similar sizes. Higher compression flow stress is connected with an increase in the coefficient of rigidity of samples and their specific contact surfaces. The dependence of apparent activation energy of alloy plastic deformation (Qdef), its relationship with the phase structure and conditions of the process of γ solid solution dynamic recrystallization is established. In the temperature conditions of the beginning of γ solid solution dynamic recrystallization process (1000–1050 °C) the Qdef value for d0 /h0 = 0,75 samples is 959 kJ/mol. The highest Qdef values for d0 /h0 = 0,75 samples of 1248 and 1790 kJ/mol are observed in the range of temperatures of intensive grain boundary γ ′-phase dissolution and coagulation (1050–1100 °C). Samples with d0 /h0 = 3,0 in this temperature range have Qdef up to 2277 kJ/mol. The apparent activation energy of plastic deformation decreases to 869 kJ/mol in the range of temperatures of homogeneous γ solid solution with grain-boundary primary and secondary carbides (1100–1150 °C). The paper provides the results of alloy sample compression at single and repeated consecutive loading with various times of pauses between deformations. It is shown that meta dynamic recrystallization under experimental conditions does not occur in the γ + γ ′-range, and occurs inertly in the γ-range.

A photoelectron imaging and quantum chemistry study of the deprotonated indole anion.

Indole is an important molecular motif in many biological molecules and exists in its deprotonated anionic form in the cyan fluorescent protein, an analogue of green fluorescent protein. However, the electronic structure of the deprotonated indole anion has been relatively unexplored. Here, we use a combination of anion photoelectron velocity-map imaging measurements and quantum chemistry calculations to probe the electronic structure of the deprotonated indole anion. We report vertical detachment energies (VDEs) of 2.45 ± 0.05 eV and 3.20 ± 0.05 eV, respectively. The value for D0 is in agreement with recent high-resolution measurements whereas the value for D1 is a new measurement. We find that the first electronically excited singlet state of the anion, S1(ππ*), lies above the VDE and has shape resonance character with respect to the D0 detachment continuum and Feshbach resonance character with respect to the D1 continuum.

Calculation of rotation-vibration energy levels of the ammonia molecule based on an ab initio potential energy surface

An ab initio potential energy surface (PES) for gas-phase ammonia NH3 has been computed using the methodology pioneered for water (Polyansky et al., 2013). Multireference configuration interaction calculations are performed at about 50000 points using the aug-cc-pCVQZ and aug-cc-pCV5Z basis sets and basis set extrapolation. Relativistic and adiabatic surfaces are also computed. The points are fitted to a suitable analytical form, producing the most accurate ab initio PES for this molecule available. The rotation-vibration energy levels are computed using nuclear motion program TROVE in both linearised and curvilinear coordinates. Better convergence is obtained using curvilinear coordinates. Our results are used to assign the visible spectrum of 14NH3 recorded by Coy and Lehmann (1986). Rotation-vibration energy levels for the isotopologues NH2D, NHD2, ND3 and 15NH3 are also given. An ab initio value for the dissociation energy D0 of 14NH3 is also presented.

CPOL Radar-Derived Drop Size Distribution Statistics of Stratiform and Convective Rain for Two Regimes in Darwin, Australia

Abstract This note builds on prior technique development related to the classification of rain types utilizing C-band polarimetric (CPOL) radar measurements. While the prior work was preliminary and limited in scope, the authors elaborate here on the basis of the drop size distribution (DSD)-based indexing technique for rain-type classification (convective/stratiform/mixed), and place it on firmer footing by testing the methodology against texture- and disdrometer-based methods as applied to Darwin datasets. A microphysical-based methodology is attractive as it links more directly to the underlying rainfall physical processes. Statistics of the DSD parameters, namely, histograms of log10(Nw) and D0, for convective and stratiform rain types across the premonsoon buildup and monsoon regimes were derived and further separated for over land and over ocean regions. The maximum value for mean D0 (1.64 mm) and the largest histogram standard deviation (0.32 mm) occurred for convective rain over land during the buildup regime. The largest differences in D0 and NW histograms were found to be for convective rain between the buildup and monsoon regimes (independent of land or ocean areas). Stratiform rain histograms were found to be very similar during the buildup regime with little land–ocean differences. However, somewhat larger land–ocean differences were found for the monsoon stratiform rain. The main histogram characteristics of the “mixed” or “uncertain” rain type were closer to the convective rain type than to stratiform, across both regimes and land–ocean areas. Additionally, the Nw versus D0 cluster of points (mean ±1σ) for convective rain agrees very well with the previously published range of values for maritime convective (equilibrium-like) DSDs.

Precise branching ratio measurements of the decaysD0→π−π+π0andD0→K−K+π0relative to theD0→K−π+π0decay

Using 232 fb-1 of e+e- collision data recorded by the BaBar experiment, we measure the ratios of three-body Cabibbo-suppressed decay rates of the D^0 meson relative to that of the Cabibbo-favored decay: B(D0 --> pi- pi+ pi0)/ B(D0 --> K- pi+ pi0) = (10.59 +/- 0.06 +/- 0.13).10^{-2} and B(D0 --> K- K+ pi0)/ B(D0 --> K- pi+ pi0) = (2.37 +/- 0.03 +/- 0.04). 10^{-2}, where the errors are statistical and systematic respectively. The precisions of these measurements are significantly better than those of the current world average values.We note that the second result differs significantly from the current world average value. Using the PDG-2006 value for D0 --> K- pi+ pi0 branching fraction, we obtain, B(D0 --> pi- pi+ pi0) = (1.493 +/- 0.008 +/- 0.018 +/- 0.053). 10^{-2}, B(D0 --> K- K+ pi0) = (0.334 +/- 0.004 +/- 0.006 +/- 0.012). 10^{-2}, where the errors are statistical, systematic, and due to the uncertainty of B(D0 --> K- pi+ pi0). The average squared matrix elements for both of the singly Cabibbo-suppressed decays are roughly a factor of sin^2 \theta_C smaller than that for the Cabibbo-favored decay and are therefore, in contrast to the corresponding two-body modes, consistent with the naive expectations.

The heat of formation of chlorine-isocyanate and the relative stability of isoelectronic molecules: An experimental and theoretical study

Accurate thermochemical data of small molecules are invaluable to the progress of every aspect of chemistry, especially in the atmosphere, combustion and industry. In this work, photofragmentation translational spectroscopy and 1st principles electronic structure theory reveal the literature value of the heat of formation of chlorine-isocyanate to be in error by more than 40 kcalmol. We report a revised experimental value for D0(Cl-NCO) = 51+/-3 kcal/mol which leads to a Delta Hf (ClNCO) = 8.5+/-3 kcal/mol. High level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit give D0(Cl-NCO) = 6.3 kcal/mol, in good agreement with experiment. In light of the present results, the destabilization of azides relative to isoelectronic isocyanates has been evaluated empirically for three pairs of related molecules. It is found to be 90-110 kcal/mol, and has been attributed mainly to the weakening of the N-NN bond relative to the N-CO bond. Electronic structure calculations employing decomposition analysis suggest that, compared to homopolar N2, the (+delta)CO(-delta) pi polarity provides better orbital interaction (charge transfer) and electrostatic attraction and results in a closer encounter and larger stabilization between the fragments and that this is the origin of isoelectronic destabilization of azides relative to the isocyanates.

Zinc oxide and its anion: A negative ion photoelectron spectroscopic study

We have recorded, assigned, and analyzed the photoelectron spectrum of ZnO−. The adiabatic electron affinity (E.A.a) of ZnO and the vibrational frequencies of both ZnO and ZnO− were determined directly from the spectrum, with a Franck–Condon analysis of its vibrational profile providing additional refinements to these parameters along with structural information. As a result, we found that E.A.a(ZnO)=2.088±0.010 eV, ωe(ZnO)=805±40 cm−1, ωe(ZnO−)=625±40 cm−1, and that re(ZnO−)>re(ZnO) by 0.07 Å. Since our measured value of E.A.a(ZnO) is 0.63 eV larger than the literature value of E.A.(O), it was also evident, through a thermochemical cycle, that D0(ZnO−)>D0(ZnO) by 0.63 eV. This, together with the literature value of D0(ZnO), gives a value for D0(ZnO−) of 2.24 eV. Since the extra electron in ZnO− is expected to occupy an antibonding orbital, the combination of D0(ZnO−)>D0(ZnO), ωe(ZnO−)<ωe(ZnO), and re(ZnO−)>re(ZnO) was initially puzzling. An explanation was provided by the calculations of Bauschlicher and Partridge, which are presented in the accompanying paper. Their work showed that our experimental findings can be understood in terms of the a 3Π state of ZnO dissociating to its ground-state atoms, while the X 1Σ+ state of ZnO formally dissociates to a higher energy atomic asymptote.

Muonic isotope effects and non-adiabatic natural orbitals for the isotopically substituted hydrogen molecular ion

The meaning of the Born–Oppenheimer approximation with respect to muonic species is discussed. The value for D0, the dissociation energy from the lowest rovibrational level, is calculated to be 255.758 kJ mol–1 for H+2, in comparison with an observed value for D0 of ⩽ 255.765 kJ mol–1; for Mu+2 the value for D0 is calculated to be 229.82 kJ mol–1. Expectation values of 〈R〉 are given for non-adiabatic wavefunctions.Nuclear and electronic natural orbitals are illustrated for the molecules T+2, H+2, Mu+2, MuT+ and MuH+.

Radiotoxicity of intranuclear 125I atoms not bound to DNA.

The radiotoxicity of 125I covalently bound to DNA is unusually high. This has been attributed both to the Auger electrons which result from the electron capture process accompanying 125I decay and to local transmutation effects which cause extensive damage to nearby structures. We introduced 125I into cell nuclei in the form of iodoantipyrine, a molecule which diffuses freely through cells, and we have compared the survival of these cells to those exposed to radiation from extracellular 125I-labelled albumin or 55Fe-labelled transferrin. We found a value for D0 of 34 rad for 125I decays occurring within the cell nucleus compared to 362 rad for extracellular 125I and 277 rad for extracellular 55Fe. Since transmutation effects are very short range and 125I was distributed uniformly throughout the nucleus rather than bound to DNA, most of the radiotoxicity of intranuclear 125I-labelled iodoantipyrine must be due to Auger electrons.

Survival characteristics of stem cells of gastric mucosa in C 3 H mice subjected to localized gamma irradiation.

SummaryThe dose-survival characteristics of gastric stem cells has been assayed in the mouse using an in situ cell cloning technique. The value for D0 is 137 rads. The repair capacity as measured in split-dose experiments, is great. Of the total sublethal injury repaired, about two-thirds is completed within the first hour. Regeneration begins promptly after an initial radiation injury, the surviving clonogenic cells doubling every 43 hours. The influence of these dose-survival and regeneration characteristics on the response of mouse stomach to a variety of dose-fractionation regimens was investigated and their relevance to radiotherapy is discussed briefly.

Kinetic Energy of Ions Produced by Photoionization of HF and F2

Kinetic energies were measured for the positive ions produced in the ion-pair formation processes HF+hΛ→H++F−, F2+hΛ→F++F− at a number of wavelengths in the region of the thresholds for these processes. The measurements prove that D0(HF) is either 5.91 ± 0.02 or 5.87 ± 0.02 eV, depending on the value of the electron affinity of the F atom. Since the latter value for D0(HF) is in good agreement with other more precise determinations, these results support the value E.A.(F) = 3.400 eV. The kinetic energy measurements also prove that D0(F2) = 1.58 ± 0.03 eV. The measurements strongly suggest that the F+ ions from F2 are produced not only in the P23 ground state but also in P13 and/or P03 states as well. At higher photon energies, the F+ ions from F2 are also produced in the D1 state. Dissociation and predissociation processes of the molecular ions are discussed.

Dissociation Energy of Diatomic Cerium and Predicted Stability of Gaseous Intermetallic Cerium Compounds

The Knudsen-cell mass spectrometric method has been used to study gaseous equilibria over the Au–Ce–CeS–BN–C system. The third-law enthalpies, ΔH0°, in kcal mole−1, of the reactions: (1) 0.5 Ce2(g)+0.5Au2(g)=CeAu(g) (2) Ce2(g)+Au(g)=CeAu(g)+Ce(g) and (3) Ce2(g)=2 Ce(g), were found to be 24.7 ± 0.14, 23.0 ± 0.16 and 58.0 ± 1.5, respectively. The corresponding second-law value for Reaction (3) is 53.4 ± 10. The reaction enthalpies for Reactions (1) and (2) were combined with the literature value for D0°(Au2) and the value of D0°(CeAu) obtained in the present investigation to yield the dissociation energy of diatomic cerium. The selected value for the dissociation energy of Ce2 is D0° = 57 ± 4 or D298° = 58 ± 4 kcal mol−1. Using the latter value and the literature value for the standard heat of sublimation of cerium, ΔHυ,298° = 101 ± 1 kcal mol−1, the standard heat of formation, ΔHf,298°, of diatomic cerium has been calculated as 144 ± 6 kcal mol−1. The stability of selected gaseous intermetallic cerium compounds has been predicted on the basis of the Pauling model of a polar bond and the experimental value for the dissociation energy of diatomic cerium. A reassessment of the dissociation energies, D0°, of LaAu, CeAu, PrAu, and NdAu [J. Chem. Phys. 52, 2956, (1970)] resulted in the values of 79.5 ± 5, 77.0 ± 3.5, 72.0 ± 5 and 70.6 ± 5 kcal mol−1, respectively.

Competitive Unimolecular Decomposition of Alkyl Radicals. Tertiary Butyl Rupture

The competitive unimolecular decomposition of vibrationally excited 3,4,4-trimethylpentyl-2·* radical was investigated. Relative and absolute rate of decomposition by tert-butyl (tBu) and methyl (Me) radical rupture were measured. Results were interpreted in terms of the Rice–Ramsperger–Kassel–Marcus (RRKM) unimolecular rate theory and lead to a value for D0°(tBu–H) of 89.0 kcal mole−1. Activation energies at 0°K for tBu and Me radical addition to olefins are discussed; some disproportionation-recombination ratios involving tBu radical were obtained.

Photoionization Study of Ion–Molecule Reactions in Mixtures of Hydrogen and Rare Gases

The reactions producing HeH+, NeH+, and ArH+ in mixtures of hydrogen with rare gases were studied by photoionization mass spectrometry. The HeH+ and NeH+ ions are produced by vibrationally excited H2+ ions; the thresholds for reaction were found to be very near the υ = 3 and υ = 2 states of H2+, respectively. Above the vibrational threshold the reaction cross section increases with vibrational quantum number and there is no evidence for a kinetic-energy threshold for these states. When accelerated to sufficient kinetic energy, H2+ ions in vibrational states below threshold react with a cross section which increases as the deficit in vibrational energy decreases. The rate constant for reaction of those vibrational states that are near or about the reaction threshold and that contribute most to the observed reaction becomes nearly constant at low repeller voltages. The threshold for the reaction producing HeH+ can be made consistent with a theoretical value for the dissociation energy D0(HeH+) = 1.835 eV. The difference D0(NeH+)–D0(HeH+) is found to be 0.25 ± 0.03 eV. This yields D0(NeH+) = 2.085 eV. In argon–hydrogen mixtures, the ArH+ is formed by an exothermic reaction of H2+ in all vibrational states with Ar and also by reaction of Ar+ ions in the P3/22 ground state and (with ∼ 30% larger cross section) of Ar+ in the P1/22 excited state with H2. The cross section has little or no dependence on vibrational energy. Chemi-ionization processes leading to the formation of ArH+ by excited H* and Ar* atoms were observed. The dissociation energy of ArH+ was found to be certainly greater than 2.647 eV and, from a tentative interpretation of the chemi-ionization processes, probably greater than 3.397 eV.

The dose-survival relationship for irradiation of epithelial cells of mouse skin.

That skin will regenerate from a single epithelial cell surviving irradiation is probable. This provides a method for estimating the numbers of these cells surviving a dose of radiation. A technique is described whereby a dose-survival relationship for skin epithelial cells was established using 29 kVp X rays. Between doses of 900 and 2,300 rads the relationship may be described by a survival curve having a value for D0 of 135 rads. The effect of a dose of radiation on skin is expressed as the number of cells surviving per unit area and not as the usual surviving fraction because it is not possible to count accurately the numbers of clonogenic epithelial cells per square centimetre of unirradiated skin. For this reason also, the origin of the survival curve and the related extrapolation number cannot be determined. Gross responses of skin are discussed in the light of epithelial cell survival characteristics. It is unlikely that mouse skin will ulcerate if more than 10–20 cells per square centimetre survive irradiation. It is also unlikely that there are any anoxic cells in the epithelium of skin or hair follicles of anaesthetised air-breathing mice.

Absorption spectrum of bromine from 6200 to 5100 Å

The absorption spectrum of the 3Π0+u–1Σ+g system of bromine between 6200 and 5100 A has been photographed at high resolution using each of the separated isotopic species 79Br2 and 81Br2. A rotational analysis of ten bands of each isotopic species has been carried out. The accepted vibrational numbering was confirmed. The constants obtained (cm–1) for each species are:- [graphic omitted]. Revised constants for the most abundant isotopic species 79 81Br2 have been calculated. The last four bands immediately preceding the onset of the continuum have also been analyzed for each species. A limiting curve of dissociation has been plotted in each case leading to an average value for D0(79 81Br2) of 15,893.1 ± 1.0 cm–1.

Theoretical growth-rate curves for Vicia faba roots under continuous radiation exposure at low dose-rate: a comparison with experimental results.

SummaryUsing models for the meristem of Vici faba proposed previously, theoretical curves of growth-rate have been computed for conditions of continuous radiation exposure at low dose-rate (1–10 rads/hr). These have been compared with experimental results. The best agreement is obtained assuming cell death at the second division following radiation damage, allowing for some gradual increase in cell cycle time during irradiation and postulating that, at any rate at the lower dose-rates, sterilised cells differentiate and contribute to root elongation. The match between theoretical and experimental curves suggests a value for D0 of about 240 rads for the ‘single hit’ type of mechanism assumed to apply at these dose-rates. It is predicted that if the cell-cycle time is varied, similar growth-rate curves should be observed for the same dose received per cell cycle (rather than for the same dose-rate).

The Effect of Zirconium on Internal Friction in Columbium

The effect of zirconium on internal friction in columbium was investigated over the frequency range of 0.5 to 10 cps. An entirely new peak was observed which was attributed to the diffusion of oxygen in the vicinity of zirconium atoms. The normal columbium oxygen peak was not observed until approximately 0.14 wt% oxygen was added to the specimens. The normal columbium-nitrogen peak was readily observed, but a zirconium-nitrogen peak was not observed until oxygen concentration was reduced below 0.1 wt%. These observations are explained on the basis of a strong attraction between zirconium and oxygen atoms. As a preliminary to this investigation, the diffusivity of zirconium in columbium at 1930°C was determined. A value for D0 and the activation energy were calculated so that the diffusivity at any temperature could be obtained from the expressionD=0.57 exp 87 000/RT.