bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of Mean Atomic Positions in Vibrating Polyatomic Molecules
Authors: Bartell L. S. 
Published: January 2005

A new method is described for calculating effects of anharmonic vibrations on bond lengths and angles in polyatomic molecules. It is shown that the quantum mechanical analog of Newton's second law of motion leads to simple equilibrium conditions from which it is possible to calculate mean displacements of atoms from positions of minimum potential energy. The method resembles the standard first-order perturbation method insofar as it relates mean displacements to mean-square displacements which can be computed from the zeroth-order harmonic problem. It gives a much more direct calculation, however, circumventing the laborious nonlinear transformations between internal and normal coordinates encountered in the perturbation method. Advantages and limitations are discussed.
Applications to several problems are outlined briefly, including isotope effects and effects of temperature on mean molecular structures. The approach, extended to crystal lattices, is shown to account for Grueneisen's relation which correlates thermal expansion and heat capacity. Numerical results of calculations are presented for H2O, D2O, NH3, and ND3, comparing the present method with other methods. Contrary to prevailing opinion, the mean apical angle of NH3 appears to be smaller than that of ND3.
NMR Studies of Hydrated Sodium Tetraborate Minerals. I. Boron—Oxygen Polyion in Borax and Tincalconite
Authors: Cuthbert J. D. , Petch H. E. 
Published: January 2005

The quadrupolar splittings of the B11 nuclear magnetic resonance (NMR) signals in single crystals of borax, Na2B4O7·10H2O, and tincalconite, Na2B4O7·5H2O, have been investigated. The electric quadrupole coupling constants, eqQ/h, and asymmetry parameters η of the electric field gradient tensors at the two unique B11 sites in the two crystals were determined to be BoraxTincalconiteeqQ/h487±1 kc/sec2544±4 kc/sec478±1 kc/sec2528±3 kc/secη0.714±0.0030.089±0.0150.473±0.0050.039±0.017.The orientations of the principal axes of the electric field gradient tensors for the above sites and their symmetry-related sites have also been determined.
The picture of the boron—oxygen polyion in borax as given by NMR is in complete agreement with the x-ray results as to numbers and coordinations of boron atoms, symmetry of the polyion and orientation of the planes of the triangularly coordinated boron atoms. The NMR results also indicate that the same boron—oxygen polyion occurs in tincalconite as in borax.
ESR Studies on Irradiated Frozen Aqueous Solutions of Sulfur Compounds
Authors: Henriksen Thormod 
Published: January 2005

Radiation-induced ESR centers in frozen aqueous solutions of sulfur compounds have been studied. Special attention has been focused on secondary radical reactions and the relative importance of direct and indirect effects. Solutions were rapidly frozen at 77°K and irradiated in vacuum at this temperature. All ESR spectra were recorded at 77°K. The irradiated samples were heat treated, either for increasing lengths of time at 110°K, or for the same period of time at successively increasing temperatures.
The ESR spectra of aqueous solutions irradiated at 77°K are composed of the ``water resonance'' and a resonance ascribed to radicals in the solute. The latter are found primarily to be induced by the direct action of radiation. This observation implies that H atoms which already have reacted at 77°K have no or very little effect in producing solute radicals.
The remaining ESR centers in water, including OH radicals, are released in the temperature range 100° to 130°K. The spectral changes in this temperature range indicate that recombination processes dominate and only a minor fraction of the ``water radicals'' interacts with the solute. Thus, in a 10% solution of glutathione, about 15% of the ``water radicals'' become effective in producing solute radicals.
The radicals induced in the solute and the subsequent secondary radical reactions seem to be more or less the same as those found when the solute was irradiated in the solid state. For solutions of some simple thiols like penicillamine the secondary reactions yield sulfur radicals above 170°K, in accordance with the results for solid penicillamine. On the other hand, no sulfur resonance appears for solutions of glutathione in spite of the fact that sulfur radicals are formed in the solid state. The resonance of the solution disappears at a lower temperature than that found necessary for the formation of sulfur raducals in solid glutathione.
Kinetics of the Pyrolysis of Organic Iodides
Authors: Benson Sidney W. 
Published: January 2005

An analysis of the data on iodide pyrolysis is made in the light of some recent work together with the newly proposed atom mechanisms for the rapid reactions of RI+HI→RH+I2. It is shown that two mechanisms seem to be rate limiting in the decompositions of alkyl iodides: RI→HI+olefin,I+RI→I+HI+olefin.These are then followed by very rapid reaction of RI+HI, which maintains the HI at a very low stationary state concentration. Mechanism A appears to govern the pyrolyses of i-PrI, EtI, t-BuI and CH3COI, while mechanism B holds for n-PrI, i-BuI and n-BuI. The pyrolysis of sec-BuI appears to involve both A and B as does that of 1,2-C2H4I2. For φCH2I, the mechanism is: I+φCH2I⇋φCH2+I2 (equilibrium),2 φCH2→(φCH2)2 (slow);and for allyl I it is: I+allyl I⇋allyl+I2 (equilibrium),allyl+allyl I→biallyl+I (slow),2 allyl→biallyl (slow).
The I2 in the system brings about a rapid conversion of biallyl to cyclohexene via abstraction of an allylic H atom.
It is shown that the racemization of optically active sec-BuI is not a Walden inversion but a simple reversible abstraction of I: I+RI*⇋ lim 21R+I2,followed by racemization in the back reaction.
Where possible, the data are analyzed quantitatively, and Arrhenius parameters are assigned to the different steps. These are discussed in the light of current data on molecular structure and bond energies.
A unique and somewhat puzzling feature of reaction B is that it appears to go as a concerted step, so that the activation energy is precisely equal to the endothermicity of the reaction. By detailed balancing, the reverse reaction would have no activation energy. This does not occur for alkyl radical attack on n-PrI but appears to be unique to I atoms. If it does occur, it is the first example of a concerted reaction involving free radicals.
Short-Lived Isomeric States of Se83 and Ge77
Authors: Arnold James R. , Sugarman Nathan 
Published: January 2005

Extractions of Br from neutron irradiated SeO3= solutions and of As from irradiated GeS3= solutions revealed the presence of short-lived isotopes of Se83 and Ge77 decaying by β−-emission to 2.4-hr. Br83 and 40-hr. As77, respectively. Direct observation of the radiations from a short-lived Se, effected by measuring the activity of Se irradiated for 20 sec. through Al absorbers, led to a half-life determination of 67±3 sec. and a β-energy of 3.4 Mev. A γ-ray was also observed. Similarly, a short-lived Ge activity was found by irradiating GeS2 with neutrons for 20 sec. and measuring the activity through Al absorbers. The half-life was determined to be 59±2 sec. and the β-energy, 2.8 Mev. The agreement between the cross sections for formation of the 67-sec. Se and the 2.4-hr. Br83 from the short-lived Se83 makes it probable that the 67-sec. Se is genetically related to the 2.4-hr. Br83. In a like manner it was shown that the 59-sec. Ge is probably identical with the short-lived Ge77.
The presence of the 67-sec. Se83 activity decaying by β−-emission to 2.4-hr. Br83 and the 59-sec. Ge77 activity decaying to 40-hr. As77 resolves the difficulty of the apparently high ``independent'' yields of Br83 and As77 in fission.
A new Se activity of 17.5±0.3 sec. half-life was also found. It appears to decay by emission of γ-radiation of ∼150 Kev. The cross section for formation of this activity by neutron activation of Se is ∼0.6 barn.
The Mechanism of the Luminescence of Solids
Authors: Williams Ferd E. , Eyring Henry 
Published: January 2005

In this paper, effort is directed toward explaining various diverse luminescent properties of solids in terms of a simple model of potential energy versus configuration coordinate. Three states of different multiplicities—a normal, metastable and an emitting state—are involved. The luminescent process consists of the excitation of an electron to the metastable level, the activated release of the electron to the emitting level, and a forbidden transition between the emitting and the ground state. With high excitation energy, the metastable state is bypassed. At high temperatures, the electron in the metastable state surmounts a larger potential barrier to undergo radiationless recombination with the activator atom.
Among those significant phenomena that have been measured experimentally and treated quantitatively by calculations based on this model are the temperature dependence of luminescent efficiency and the effect of type and wave-length of excitation on this temperature dependence; the three types of phosphorescence—spontaneous, metastable, and recombination phosphorescence; the phenomena of two-stage afterglow and the effect of type of excitation and temperature on the two stages; the relationship between buildup and afterglow kinetics; and the release of electrons from metastable states by thermal energy. The concept of the Absolute Rate theory are used to clear up the essential criteria for the different types of afterglow.
A detailed theoretical analysis of ``glow curves'' is presented and quantitatively applied to improved glow curves obtained at linear rates of heating 100 times slower than those previously reported. The slower rates of heating allow one metastable level to be operative at a time. Both monomolecular and bimolecular mechanisms are treated, and it is concluded that glow curves result from discrete metastable states that are emptied thermally by predominantly monomolecular kinetics. The explicit expressions for the specific rate constants involved in the release of electrons from metastable states are calculated.
The Effect of High Mechanical Stress on Certain Solid Explosives
Authors: Bridgman P. W. 
Published: January 2005

Eleven different solid explosives have been subjected at room temperature to stresses of the order of those which prevail in the detonating front. Two types of stress were applied. The first consisted of a hydrostatic pressure of 50,000 kg/cm2, on which was superposed a shearing stress sufficient to produce shearing deformations of the order of 60 radians. The second type consisted of a hydrostatic pressure of 100,000 kg/cm2, with a comparatively small superposed shearing deformation. Seven of the eleven explosives survived stress of the first type without detonation. Only four of the explosives were subjected to the second type of stress; three of these survived without detonation. It is probable that in those cases where detonation occurred secondary effects were responsible, such as striking of sparks by fractured fragments of steel. The general conclusion is drawn that stresses of these magnitudes, without the cooperation of high temperature, cannot be counted on to produce detonation.
Incidentally it was found that yellow ammonium picrate is transformed irreversibly to the red form by the first type of stress. Values were obtained for the plastic flow stress as a function of hydrostatic pressure. The strength increases approximately linearly with pressure.
Dynamics of a Square Lattice I. Frequency Spectrum
Authors: Montroll Elliott W. 
Published: January 2005

The distribution of frequencies of normal modes of vibration of a monatomic square lattice is obtained as a function of the force constants of the lattice. Since the forces between pairs of atoms in the lattice are short ranged, interactions between all atoms, other than nearest and next nearest neighbors, are neglected.
Two constants, α and γ, are used to describe the lattice. α is a force constant derived from the interaction of nearest neighbors, and γ is that derived from the interaction of next nearest neighbors.
According to the Debye continuum theory the frequency spectrum, or density of normal modes, should be a linear function of the frequency. In the Born-Karman atomic model used in the present paper it is shown that this is only the case at very low frequencies and that there actually exist two sharp infinities in the frequency spectrum.
We define g(ν) so that g(ν)dν is the number of normal modes of vibration with frequencies between ν and ν+dν. A closed expression involving complete elliptic integrals is obtained for g(ν) when τ=[1+(α/2γ)]−1=⅓. For general values of τ&lt;½, g(ν) is shown to have the following properties:
(a) The largest frequency, νL, occurs at νL=[(4α+8γ)/4π2M]12,where M=mass of each atom.
(b) There is an infinity in g(ν) at ν=νLτ½.
(c) The second infinity is at ν=νL(1−τ)12 if τ&lt;15, and ν=νL(1+3τ)/4τ12 if τ&gt;15.
(d) As ν/νL→0, g(ν) is linear in ν.
Absorption Spectrum of Borazole in the Vacuum Ultraviolet
Authors: Platt J. R. , Klevens H. B. , Schaeffer G. W. 
Published: January 2005

The absorption spectra of triborine-triamine or borazole, B3N3H6, has been studied with a fluorite vacuum spectrograph in the region 2250–1700A in n-heptane solution. The compound was prepared by the reaction between diborane and ammonia.
Four diffuse bands are found, starting at 1995A, with spacing about 900 cm−1. These seem analogous to the 2000A bands of benzene, but the intensity is about 10 times smaller. A strong continuum, like the 1800A benzene peak, has its maximum at 1720A or below. No bands like the benzene 2600A group were found, though they would have been seen if their intensities had been only 1/20th that of the latter.
The spectrum of a boron hydride, B5H9, has also been obtained but shows only a featureless continuum in this wave-length region.
The Relationship between the Brunauer-Emmett-Teller Adsorption Isotherm and the New Isotherm of Jura and Harkins
Authors: Livingston H. K. 
Published: January 2005

Values for the surface pressure and area of molecules adsorbed on solid surfaces can be calculated from the adsorption equation of Brunauer-Emmett-Teller. Over a wide pressure range these calculated values are in approximate agreement with the two-dimensional equation of state for vapor-condensed films. Since the adsorption equation of Jura and Harkins was derived from this same equation of state, it is concluded that for a great many experimental isotherms, the mathematical agreement between the two adsorption equations is so good that extremely accurate experimental work would be necessary to determine which equation was more nearly correct.
The Brunauer-Emmett-Teller equation gives calculated curves on Gregg-type plots that agree qualitatively with those reported by Gregg for multi-layer adsorptions. Surface-area values obtained from these curves by Gregg's X-point method are generally considerably higher than those that would be obtained by the method of Brunauer-Emmett-Teller.
The limiting area occupied by a molecule (i.e., in a mono-molecular layer) as calculated by the method of Harkins and Jura appears to decrease with decreasing energies of adsorption (i.e., decreasing values of c in the Brunauer-Emmett-Teller isotherm). It is suggested that this decrease is artificial, rather than real, and results from the assumption that the constant a in the two-dimensional equation of state does not vary with changes in the nature of the solid adsorbent.
It is not possible at the present time to suggest that one of the isotherms is to be preferred to the other on theoretical grounds. In general, preference should be given to the one which fits experimental data over the broader pressure range.
Short-Lived Halogen Fission Products
Authors: Sugarman Nathan 
Published: January 2005

Half-life values have been determined for some short-lived Br and I fission products. The chemical isolation of Br from irradiated uranyl nitrate led to a half-life for Br85 of 3.00±0.05 min. The energy of the β-radiation of Br85 was found to be 2.5 Mev by Feather analysis of the Al absorption curve. The half-lives found for Br87 and Br88 by extraction of the Kr daughter activities from AgBr precipitates were 56.1±0.7 sec. and 15.5±0.3 sec., respectively, on the basis of a 3-min. half-life for Br85. Attempts to measure the half-lives of Br89 and Br91 by extraction of the descendant Sr activity were unsuccessful because of the absence of activity. The identity in half-lives of Br87 and the 55.6-sec. Br delayed neutron emitter makes it probable that the mass assignment of the delayed neutron emitter is 87.
The half-life of I137 was found to be 19.3±0.5 sec. by extraction of Xe137 from AgI precipitates, on the assumption of constant chemical yield of the Xe extraction. Isolation of Cs138 both from the gas separated from AgI precipitates and from the precipitates directly led to a half-life determination for I138 of 5.9±0.4 sec. Extractions of Ba149 yielded a value of 2.7±0.1 sec. for the half-life of I139. The absence of Ba140 activity in AgI precipitates made it impossible to determine the half-life of I140. Because of the agreement in half-lives of I137 and the 22.0-sec. I delayed neutron emitter it is probable that the two are identical.
The low retention of the decay products of the short-lived halogens by the silver halide precipitates led to an estimate of 20 sec. for the ``setting'' time of the precipitate.
The Assignment of the Vibrational Spectra of Ethyl Mercaptan and the Ethyl Halides, and the Characterization of an SH Deformation Frequency
Authors: Sheppard N. 
Published: January 2005

An assignment is given for all the fundamental modes of vibration of the ethyl mercaptan molecule from the observed vibrational spectra. By analogy the observed frequencies in the spectra of ethyl chloride, bromide, and iodide are also assigned to normal modes of vibration of these molecules.
Evidence is presented that one of the deformation modes of the SH linkage in mercaptans has a characteristic frequency lying between the limits of 800 and 900 cm−1. This frequency is usually stronger in the Raman spectrum.
The Tensile Strengths of Liquids. I. Thermodynamic Considerations
Authors: Benson Sidney W. , Gerjuoy Edward 
Published: January 2005

An investigation is made of the thermodynamic stability of liquids under tension. Comparisons of the Helmholtz free energies show that small samples of liquid under tension are unstable with respect to two-phase liquid-vapor equilibrium at the same volume and temperature.
Defining the tensile strength as the negative pressure at which (∂P/∂V)T=0 for the liquid, it is possible to calculate ``maximum'' possible tensile strengths from equations of state. The van der Waals and Berthelot equations in reduced form can be adapted to such explicit calculation and give values much lower, and therefore much closer to experimental values, than previous calculations. For non-associated liquids at 27°C, the van der Waals maximum tensile strengths are about 150 atmos. whereas the Berthelot values are about 750 atmos. The temperature dependence for the two equations is about 1 and 6 atmos. °C, respectively.
Comparisons with observation of the calculated reduced liquid volume, energy of vaporization, coefficient of thermal expansion, and bulk compressibility support the use of the van der Waals and Berthelot equations in computing liquid properties.
Infra-Red Spectra of Propane, 1-Deuteropropane, and 2-Deuteropropane and Some Revisions in the Vibrational Assignments for Propane
Authors: McMurry H. L. , Thornton V. , Condon F. E. 
Published: January 2005

The infra-red spectra of propane, 1-deuteropropane, and 2-deuteropropane are presented. The spectrum of propane does not have the bands at 720 and 1179 cm−1 reported by Wu and Barker.
The vibrational modes of the three molecules are described. The 748-cm−1 band in the propane spectrum is unambiguously assigned to rocking of the CH2 group about an axis normal to the molecular axis and in the C3 plane; and the 1053-cm−1 band is unambiguously assigned to rocking of the CH2 group about an axis normal to the C3 plane.
Unambiguous assignments for the remaining bands below 1350 cm−1 in the propane spectrum were not possible without an elaborate theoretical treatment beyond the scope of this paper.
The Exchange Reaction between the Hydrogen Halides and the Halogens in the Gaseous State
Authors: Dodgen Harold W. , Libby W. F. 
Published: January 2005

It has been shown that hydrogen fluoride and fluorine gases do not undergo an exchange reaction at room temperature and that heating to 200°C for a matter of an hour or so in a brass vessel is necessary to accomplish exchange. Evidence is obtained that even in this case the observed exchange is heterogeneous and catalyzed by the metal fluorides on the wall of the vessel. Illumination by the light of a mercury arc did not accomplish the exchange under conditions such that an activation free energy of some 9 Kcal/mole for the reaction between a fluorine atom and the fluorine molecule or fluorine atom and HF molecule would have been necessary to prevent exchange.
A rapid exchange reaction in the dark at room temperature has been observed to occur between chlorine and HCl in the gaseous state. This is taken as evidence that the hydrogen halides exchange with the halogens through the formation of an intermediate complex of the general formula HX3, and some discussion of the improbability of the alternative atomic mechanism is given. The non-existence of the HX3 mechanism in the case of the fluorine system is explained by the absence of electrons in the higher shells which are thought to be the main bonding forces involved in the stabilization of the HX3 complex in the case of chlorine, bromine, and iodine, and also by the polar character of the hydrogen-fluorine bond in HF, increasing the probability of an alternative HX3 complex formation in which the hydrogen rests between the fluorine on the HF molecule and the fluorine molecule itself, thus keeping it clearly labeled and rendering interchange on dissociation of the complex unlikely.
Structural Investigations by Means of Nuclear Magnetism. I. Rigid Crystal Lattices
Authors: Gutowsky H. S. , Kistiakowsky G. B. , Pake G. E. , Purcell E. M. 
Published: January 2005

Experimental absorption line shapes at nuclear magnetic resonance are given for several simple assemblies of nuclei, with spin ½, in the solid state at temperatures between 90° and 95°K. Analysis of these data is facilitated by the theory of Van Vleck which relates the second moment of the absorption line in a rigid lattice to nuclear spins, gyromagnetic ratios, and internuclear distances, and which provides, therefore, an objective and general method for determining structural parameters from the experimental line shapes.
1,2-dichloroethane exhibits a proton resonance with line structure characteristic of nuclear magnetic moments interacting in pairs to produce the broadening of the absorption line. Consideration of both fine structure and second moment leads to an inferred H–H distance of 1.71±0.02A in the —CH2Cl group. In conjunction with the expected C–H bond distance of from 1.09A to 1.10A, this implies that the H–C–H bond angle is between 4° 30′ and 9° less than tetrahedral. Absorption line shapes for the proton resonance in 1,1,1-trichloroethane and ammonium chloride are given as characteristic respectively of equilateral three-spin and tetrahedral four-spin systems. Less conclusive studies of perfluoroethane and diborane are presented. A detailed analysis of data on ammonium fluoride, chloride, and bromide yields a value of 1.025±0.005A for the N–H distance in the ammonium ion. Some general aspects of the use of nuclear magnetism in structural investigations are discussed briefly.