bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nucleation in Very Rapid Vapor Expansions
Authors: Kantrowitz Arthur 
Published: January 2005

In the Volmer theory, sub-critical droplets (embryos), with vapor pressure greater than their surroundings, nevertheless, grow statistically, because they exist in sufficiently greater numbers than neighboring larger droplets. Thus the formation of nuclei against the thermodynamic barrier presupposes the presence of very large numbers of embryos of all sizes.
An approximate lower bound for the time (nucleation time) required for the formation of this system of embryos can be calculated readily by (1) neglecting the thermodynamic barrier which impedes their formation; (2) assuming that when droplets contain a certain supercritical number, Γ, of molecules they grow very rapidly because their vapor pressure is considerably lower than their surroundings; (3) assuming that the formation of the embryo system begins when the vapor first becomes saturated. The equation for the rate of formation of embryos then reduces to the heat conduction equation yielding a simple solution. The lower bound sought is found to be inversely proportional to the fourth power of the degree of supercooling. Comparison with the experiments of Wegener and Smelt indicates that in some nozzle expansions the occurrence of nucleation is determined by this process.
On this theory the thermal accommodation coefficient which determines the heat transfer and especially the accommodation coefficient for growth, which determines the probability of a molecule sticking to the surface, play a much more prominent role than they do in the Volmer steady-state theory. Comparison with experimental time lags for the condensation of H2O in air at −30 to −60°C gives the order of magnitude of the accommodation coefficient for growth as 5×10−4.
The Diffusion of Hydrogen Through Nickel
Authors: Post C. B. , Ham W. R. 
Published: January 2005

The diffusion of hydrogen through commercial and very pure anode nickel has been studied in a precision manner throughout the temperature interval 1100° to 150° Centigrade. It was found that the diffusion rates vary in a perfectly regular manner throughout this region, except for a discontinuity at the Curie point, namely near 360°C.
A very exact agreement with the formula R = ATzpy ×exp (—b/T) was found in all cases. After long heat treatment with hydrogen the value of y in the above equation for anode nickel becomes +0.50±0.01 with the possible exception of a region within 3° of the Curie point. All the nickel used had isotherms whose slope at the start of observations was a maximum in the Curie region and markedly greater than 0.5, but which approached 0.5 as the heat treatment, ordinarily considered as having a decarburizing effect, progressed.
The magnetic transition as shown by diffusion is abrupt, the isobars below the Curie region being quite as straight as above. There is always a sudden drop in the value of b as calculated from the simple equation R = A exp (—b/T) at the Curie point, the value changing in the purest nickel from 6600 to 5800 with rising temperature. No systematic breaks appear in the isobars at high temperatures, such as found in pure iron, but nevertheless the value of z indicates that the diffusing hydrogen possesses appreciable energy within the lattice.
The Curie region shows marked hysteresis, and is similar to the Curie region of pure iron in this respect.
Existing theories of ferromagnetism seem to require modification, inasmuch as the Curie transition in nickel appears to take place about as abruptly as the body-centered-face-centered transition in iron. The loss of magnetism at the Curie transition is essentially an atomic phenomenon and should not be associated primarily with conditions in aggregates of atoms or atomic domains. During the transformation for a finite time, there appears to be an additional electron in the valence shell of some nickel lattice points.
A possible description of the process of the change from the ferromagnetic to the paramagnetic condition in the transition elements is that an electron is moved from the 3d shell to one of the 4 levels, followed more or less quickly by a drop of another 4-level electron back to such a 3d level as to result in the pairing of electron spins in the 3d shell.
Molecular Interaction in Mixed Monolayers II. Unstable Mixtures with Unsaturated Acids
Authors: Florence Robert T. , Harkins William D. 
Published: January 2005

This investigation concerns the effect of the form of a molecule, with otherwise identical composition and structure, on its binding to the acidic or basic water of the subphase and to the molecules of the film itself. The binding to the water by the carboxyl group should be approximately the same for stearic acid and for the unsaturated acids, oleic and elaidic acid, with the double bond in the middle of the hydrocarbon chain. By compression of the film oleic acid may be squeezed out practically completely, from a mixed monolayer in which a saturated long chain alcohol, acid, or amine is the other constituent. Thus the energy of binding of the oleic acid to the other molecules in the film is weaker than that between the saturated molecules. However, earlier work in this laboratory has shown that the presence of the double bond does not decrease, but very slightly increases, the attraction between molecules.
Thus it seems to be the shape of the molecule which reduces the energy of binding of oleic acid in the film. Oleic acid is a cis form, so a nine carbon atom chain R2 is bent backward with respect to the other 9C chain R1 which ends in the carboxyl group. It may be assumed that the whole molecule is free to rotate, with the carboxyl group in contact with the water, and that the group R2 is free to vibrate or ``flagellate.'' Thus the oleic acid molecule would occupy a larger area than a saturated acid and this increased distance together with a lessening of the length of the contact between this and the other molecules in the film, decreases greatly the energy of binding. Space models of oleic and elaidic acid have been used in the study of these relations.
By a greater straightening of the chain, as in the transcompound, elaidic acid, the energy of binding should become intermediate between that of oleic and stearic acid, and much above that for oleic acid. On this basis compression should segregate elaidic acid slightly from the mixed film, but by no means completely, and this is what the experiments demonstrate.
The Infra-Red Absorption Spectrum of Methyl Alcohol
Authors: Borden Avis , Barker E. F. 
Published: January 2005

Using a grating spectrometer having a KBr foreprism the spectrum of methyl alcohol vapor was studied in the region from 2.5 to 26μ. This molecule has bands at 3683, 2978, 2845, 2054, 1477, 1455, 1340, 1034.18 cm—1 and a very broad band extending from 860 to beyond 380 cm—1. These bands are typical perpendicular and parallel bands and indicate that the molecule is only slightly asymmetric.
From the fine structure of the 1034.18 cm—1 parallel band and from certain assumptions about the structure of the molecule the two largest moments of inertia, A and B, were found to be 35.18 and 33.83×10—40 g cm2, respectively. It was not possible to measure C directly but it was estimated to be approximately 6.8×10—40 g cm2.
The low frequency band is probably due to the vibration of the hydroxyl hydrogen atom perpendicular to the O–H bond and perpendicular to the figure axis of the molecule. The presence of this band indicates that the hydroxyl group is not free to rotate, at least in the ground state. There is evidence of rotation in the structure of the band near the high frequency edge. The spacing increases toward high frequencies and finally there is a group of lines having a spacing of about 40 cm—1 between 600 and 860 cm—1. Since these lines are very weak and occur at such high frequencies it appears that free rotation exists only in states of high excitation. A quantitative study of free rotation in a symmetric molecule has been made. This investigation indicates that in a first approximation free rotation should give rise to groups of lines having a spacing of about 40 cm—1 between each group.
Photochemistry in the Photo-Ionization Region. II. Photochemistry of Methane, Ethane, and Ethylene at Wavelengths below 900 Å
Authors: Walker D. C. , Back R. A. 
Published: January 2005

The photolysis of methane has been investigated, using light from a microwave discharge through helium which is thought to have consisted mostly of the strongly self-reversed 584-Å resonance line. A windowless fast-flow separation system was used to separate the light source from the photolysis vessel. Methane pressure was varied from 0.001 to 0.3 mm, with helium as a carrier gas making up a total pressure of 1.85 mm.
Products were correlated with saturation ion-currents, ranging up to 25 μA, which were measured in the photolysis vessel. The main products were hydrogen, ethane, ethylene, and acetylene, with estimated yields of 4.0, 0.37, 0.31, and 0.11 molecules per ion-pair, respectively. Smaller amounts of propane and propylene, and traces of C4 hydrocarbons, were also observed. Formation of unsaturated polymer was inferred from the carbon deficit of the volatile products. The effects of adding ethylene and neon to the system were studied, and in some experiments an electric field was applied.
The photolyses of ethane and ethylene were also briefly investigated. Hydrogen was the only product measured, with yields ranging from 1.0 to 1.9 and from 0.8 to 1.2 molecules per ion pair from ethane and ethylene, respectively.
Mechanisms are presented to account for the observed results. It was concluded that both direct photolysis and helium sensitization were important primary processes in all three hydrocarbons.
Vibrations of the OH Ions in Muscovite
Authors: Vedder W. , McDonald R. S. 
Published: January 2005

Pleochroism of the infrared absorption of muscovite has been measured under moderate resolution. The results are discussed in terms of the idealized mica structure.
From the pleochroism of the OH stretching band, orientation of the vibrational transition moments can be determined. These moments are tilted out of the cleavage plane by about 16°. Their projection onto the cleavage plane makes an angle of about 32° with the b axis. These directions furnish approximations to the orientation of the OH ions, but the danger of equating the two is stressed. Vibrational coupling is small. This result has been used to decide rather conclusively between two models of muscovite which differ in the orientation of the OH ions.
The librational motion has been studied directly, as well as in combination bands with the OH fundamental. It is shown that the SiO lattice also gives rise to combination bands with νOH.
Fundamental Vibrational Frequencies in Ketene and the Deuteroketenes
Authors: Cox A. Peter , Esbitt Alan S. 
Published: January 2005

Accurate microwave relative intensity measurements have been made on rotational transitions of ketene and its deutero derivatives in the ground and first vibrational states. The results allow the three lowest fundamental frequencies of these molecules to be positively determined. For CH2CO these modes are found to be 443, 527, and 617 cm−1. The lowest frequency is nearly 100 cm−1 lower than any fundamental previously cited from infrared data for ketene.
To substantiate the microwave results solid-state infrared spectra of the molecules at −192° have been investigated in the region 300–4000 cm−1. The low-frequency spectra are in good agreement with the microwave data, and a complete analysis allows the nine fundamentals of CH2CO, CHDCO, and CD2CO to be evaluated. The three lowest fundamentals of CH2CO in the solid are found at 433, 513, and 613 cm−1.
The thermodynamic properties of ketene have been recalculated.
Spin Resonance Spectra of Substituted Aromatic Ions: Perturbation Model
Authors: Brown Thomas H. , Karplus Martin , Schug John C. 
Published: January 2005

By use of a perturbation approach, the valence-bond method is applied to weakly substituted benzene positive and negative ion radicals. Small changes in the Coulomb integrals are introduced to remove the degeneracy present in the unsubstituted case. The case of D2 symmetry, which corresponds to para-disubstituted benzene, is treated in detail in terms of a basis set consisting of eighteen valence-bond functions. Previously given formulas are used in obtaining the secular equation, spin densities, and charge densities for these ion-radical systems.
To test the usefulness of the method, spin densities of several of the methyl-benzene negative ions are compared with hyperfine constants determined from the ESR spectra of these ions. The theory accounts qualitatively for all of the experimental results, and in most cases the agreement between the measured and the calculated hyperfine constants is semiquantitative. Still better agreement may come with improved knowledge of the molecular integrals involved and of the degree of mixing of nearly degenerative states. Predictions are made for the spin densities in other methyl-benzene negative ions as well as the yet to be observed positive ions.
H2-Transfer Reactions in the Gas-Phase Radiolysis of Hydrocarbons
Authors: Ausloos P. , Lias Sharon G. 
Published: January 2005

The radiolysis of cyclohexane has been investigated in the presence of varying concentrations of acetylene, ethylene, propylene, butene, and cyclopropane. On the basis of a number of observations, it is concluded that, in all cases, the H2-transfer reactionCnHm+cyclo−C6H12+→CnHm+2+C6H10+does take place. No extensive rearrangement occurs in the collision complex. For instance, a transfer of H2 to CD3CDCD2 results exclusively in the formation of CD3CDHCD2H, while an H2 transfer to (CD2)3 leads to the formation of CD2HCD2CD2H. Relative rate constants for the transfer of an H2 molecule to CH3CHCH2, 1-C4H8, iso-C4H8, 2-C4H8, C2H4, and C2H2 are, respectively, 1.00, 0.68, 0.27, 0.10, 0.11, and 0.072.
Similar variations in the relative rate constants of the H2−-transfer reactionCnHm++cyclo−C6H12→CnHm+2+C6H10+are noted.
The following additional information was derived in the course of this study:
(1) When cyclopentane or n-pentane is substituted for cyclohexane in the reaction mixture, the H2-transfer reaction again occurs. Under comparable experimental conditions, the probability of the H2-transfer reaction is proportional to the yield of the parent ion as derived from the 70-eV mass-spectral cracking patterns.
(2) An increase in the pressure of cyclopentane, from 12.7 to 210 mm, leads to approximately a 50% increase in the yield of the parent ion of cyclopentane.
(3) The parent cyclohexane ion undergoes a charge transfer to NO at a rate which is comparable to the rates of the H2-transfer reactions. O2 does not interact with the parent ion.
(4) The cyclopropane-d6 parent ion reacts with cyclo-C6H12 to form CD3CDHCD2H, indicating that this ion acquires the propylene ion structure prior to or during reaction.
Ion—Ion Interactions in Rare-Earth-Doped LaF3
Authors: Brown M. R. , Whiting J. S. S. , Shand W. A. 
Published: January 2005

A systematic study of quantum efficiencies and lifetimes has been carried out for the visible fluorescences of Pr3+ in single-crystal LaF3. An analysis of the results as a function of Pr3+ concentration is given in terms of a two-site model in which a Pr3+ ion can either be in an isolated site or in a site where it is coupled to other impurity ions. This model leads to ion—ion interaction ranges varying from ∼5 Å (nearest neighbor) to ∼12 Å depending on the fluorescent level studied. Throughout this range of interaction lengths, Dexter's model of electrostatic ion—ion interaction shows that the dominant contribution comes from the quadrupole—quadrupole term. Temperature effects in the interaction are consistent with the lack of exact resonance between the electronic levels. It appears that the lattice can readily absorb excess energy up to ∼1000 cm−1.
A set of samples doped with a second rare earth (Ce3+, Nd3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+) has demonstrated the existence of selection rules for ion—ion interaction in addition to energy-matching requirements. The system 0.5% Pr3+: x% Ce3+ has been studied in more detail.
Photochemistry of Metal Solutions. II. Flash Photolysis of Alkali Metals in Ethylamine
Authors: Ottolenghi Michael , Bar-Eli Kedma , Linschitz Henry 
Published: January 2005

Flash-photolysis studies have been made on Li, K, Rb, and Cs solutions in ethylamine, over a range of temperature and concentration. Such solutions typically show three bands near 650 (V), 850 (R), and 1300 (IR) mμ. These are assigned, respectively, to a cation-centered monomer, a dimer, and a solvated electron. In K, Rb, and Cs solutions, flashing at wavelengths shorter than 500 mμ causes initially a bleaching of V and enhancement of IR. This is followed by a growing in of R, but at a rate quite different from that of IR decay. Another precursor X of the R transient is therefore postulated. The R transient finally reverts back to V. The ratio of the yields of the IR and R transients is constant, independent of excitation wavelength, metal concentration and fractional conversion. From this it is inferred that X and IR have a common origin. Direct reversible photolysis of the original R-band also occurs, leading to an infrared transient which decays back to R in a second-order process. The rate constants all decrease, in passing from K to Cs. In Li solutions, photolysis of V results in enhanced IR absorption followed by direct back reaction to V without the intermediate R-transient stage.
The nature of the various species and transients is discussed. It is suggested that X may be a long-lived excited state of the monomer V, the metastability being due to Franck—Condon effects. Alternatively, X may be an unstable monomer with an ion-pair structure, similar to that postulated for the monomer in liquid ammonia.
Influence of the Dielectric Constant on the Yield of Free Ions Produced during Radiolysis of a Liquid
Authors: Freeman G. R. , Fayadh J. M. 
Published: January 2005

The γ-radiation-induced conductance of liquid diethyl ether is consistent with the previously developed theory.
The following values of G(free ion) were determined by the conductance method: n-hexane, 0.10; cyclohexane, 0.10; p-dioxane, 0.05; n-butyl ether, 0.11; ethyl ether, 0.19; n-butyl bromide, 0.27; n-butyl chloride, 0.39.
Values of G(free ion) in other systems were obtained from spectroscopic and chemical studies reported in the literature.
G(free ion) is roughly proportional to the static dielectric constant of the liquid, over the range studied. A theory is presented which explains the results. It appears that the slowed-down secondary electrons are ``trapped'' in the liquid and solvated before undergoing geminate recombination, even in alkanes.
Solvated electrons in alkanes would probably have a charge-transfer type of absorption spectrum, with a broad absorption maximum in the infrared.
The major portion of ion pairs that undergo geminate recombination in these liquids does so in a period of 10−10±1 sec.
A general mechanism is formulated for the initial stages of the ionic part of a liquid-phase radiolysis reaction.
Theory of Shifts of Vibration—Rotation Lines of Diatomic Molecules in Noble-Gas Matrices. Intermolecular Forces in Crystals
Authors: Friedmann H. , Kimel S. 
Published: January 2005

It is shown that the observed shift of infrared lines of diatomic molecules trapped in noble-gas crystals can be considered to be made up of a ``vibrational'' shift of the band center with a superimposed ``rotational'' shift dependent on the rotational quantum number J. These shifts were studied by means of a detailed analysis of the molecular motion. Application of the Born—Oppenheimer method shows that the intermolecular potential energy, which governs the rotational and translational motions of a system of electronically unexcited molecules, depends on v, the intramolecular vibrational state. This dependence is analyzed using an extension of the principle of corresponding states, thus introducing v-dependent Lennard-Jones force constants ε and σ. Explicit values of the variation with v of ε and σ have been calculated taking into account dispersion, induction, and repulsion forces. In this way vibrational shifts of HCl, DCl, HBr, and CO in Ar, Kr, and Xe matrices were obtained.
Rotational shifts are interpreted by assuming that the trapped molecule is free to rotate about a point which does not coincide with the molecular center of mass. The resulting coupling between the rotational motion of the molecule and its constrained translational motion in the lattice is treated as a perturbation. The relation between this theory and the crystal-field theory is discussed.
Theory of Hyper-Raman Effects (Nonlinear Inelastic Light Scattering): Selection Rules and Depolarization Ratios for the Second-Order Polarizability
Authors: Cyvin S. J. , Rauch J. E. , Decius J. C. 
Published: January 2005

The symmetry properties of the third-rank tensor β which comprises the set of coefficients of quadratic terms in the expansion of the induced-dipole moment in the electric field are investigated, and the various linear combinations belonging to the irreducible representations are tabulated for the important molecular symmetry groups. Depolarization ratios are calculated for a sample composed of randomly oriented molecules (liquid phase). Examples of the selection rules in both liquid and crystalline phases are discussed, and these selection rules are contrasted with the ones appropriate for infrared absorption and the ordinary Raman effect.
Molecular modes allowed in the infrared are always allowed in the hyper-Raman effect and have a depolarization ratio (for linearly polarized incident radiation) ≤⅔, while allowed hyper-Raman transitions forbidden in the infrared have a depolarization ratio of ⅔.
Fluorescence and Defect Fluorescence of Anthracene at 4.2°K
Authors: Helfrich W. , Lipsett F. R. 
Published: January 2005

Previous measurements of space-charge-limited hole currents have shown that anthracene crystals, even if very pure, contain large numbers of hole traps distributed exponentially in depth. Arguments are presented that these defects, if structural, should also act as singlet excitation states below the singlet exciton band. In order to detect such excitation states, the following experiments were carried out at 4.2°K: (1) observation of fluorescence with ordinary excitation within the singlet absorption band (vexc&gt;v0–0) to check the purity of the anthracene crystals, (2) observation of fluorescence with defect excitation (vexc&lt;v0–0), (3) observation of both kinds of fluorescence after the crystals were annealed at 130°C.
Some of the ordinary fluorescence spectra showed sharper lines than spectra previously reported. These lines appeared as doublets. Three kinds of defect fluorescence, which depended on the crystal used and on vexc, were observed: (a) fluorescence without structure in its excitation and emission spectra, (b) fluorescence with structured emission spectrum, (c) strong background emission in the ordinary fluorescence. No indications of chemical impurities were found. The results indicate that disordered regions, point defects, and dislocations play a significant role in the fluorescence process.