bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrasonic Dispersion Observed by Optical Diffraction. II. Ammonia
Authors: Strauch J. G. , Decius J. C. 
Published: January 2005

The velocity of sound in NH3 at 300°K has been measured at a frequency of about 1 MHz over the pressure range from 6 atm down to ½ atm, employing the optical diffraction method. All measured velocities were lower than the low-frequency ideal-gas limit of 436 m sec−1. Interpreting this result as evidence of nonideality and not dispersion, we fitted the data to the formula V2=Vi2(1+sp) and obtained Vi2=(19.122±0.034)×104 m2 sec−2 and s=(−13.9±0.05)×10−3 atm−1. The ideal velocity squared, Vi2, agrees with the spectroscopic value to within 0.05% and shows that no loss of vibrational heat capacity occurs up to f/p=2.1 MHz atm−1.
The nonideality correction term s is used to recalculate nonideality corrections to the data of previous workers, and it is suggested that the vibrational relaxation time in NH3 may be of the order of 6 nsec at 300°K.
Photolysis of Liquid Water at 1849 Å
Authors: Sokolov Uriel , Stein Gabriel 
Published: January 2005

The photolysis of pure water and of aqueous solutions of alcohols (methanol, ethanol, and isopropanol) at 1849 Å, when the light is absorbed by the water, proceeds according to[Complex chemical formula]The quantum yield for the formation of the geminate pair (H+OH) is φ=0.45 at room temperature. Scavengers compete with the recombination of the geminate pair according to diffusive inhomogeneous kinetics. A value of 3.9×10−6 sec½ is obtained for the Noyes parameter a, in agreement with theory. The results exclude direct interaction between scavenger and excited water molecules and also exclude molecular processes in the formation of H2. Solvated-electron formation has a quantum yield of ≤0.045. Isotope experiments support the conclusions.
In the reaction with the alcohols, that of the OH radicals determines the competition with secondary geminate recombination. From the results a value of k(dim)/k(dis)=6.6 is obtained for the ratio of dimerization to disproportionation of CH2OH radicals.
Cooperative Exciton States in Molecular Crystals
Authors: Jortner Joshua , Rice Stuart A. 
Published: January 2005

In this paper we calculate the transition probability for excitation of double-exciton states in absorption and emission processes in molecular crystals. The formalism is based on the tight-binding approximation, treating the intermolecular electrostatic and exchange interactions and the interaction with the radiation field by perturbation theory. It is found that:
(1) A major contribution to the transition probability for cooperative excitation to electronic states arises from intermolecular Coulomb interactions, while the contribution of intermolecular electron-exchange interactions is relatively small.
(2) Contributions to the transition probability from high-order-transition multipole interactions are of considerable importance.
(3) Approximate selection rules for cooperative electronic excitation imply that for one component the initial and final states are of the same parity, while for the second component the transition is symmetry allowed.
(4) Theoretical evidence is obtained for the appearance of double-excitation bands in the infrared spectra of solids in the overtone region.
(5) A major contribution to the intensity of the double-vibrational-exciton states arises from an intermolecular Fermi resonance effect.
(6) The direct detection of the radiative annihilation of a double-exciton state is not likely to be experimentally feasible.
Out-of-Plane Bending Frequencies in Trimethylene Sulfide from Microwave Intensity Measurements
Authors: Harrington Howard W. 
Published: January 2005

The first four out-of-plane ring-bending energy separations in trimethylene sulfide[Complex chemical formula]have been determined from microwave intensity measurements on the 000−101, 634−633, and 423−422 rotational transitions in X band.
These separations are 0, 141, 15, and 85 cm−1 for the 0–1, 1–2, 2–3, and 3–4 transitions, respectively, indicating a bent configuration for the ring.
The uncertainty in these numbers is about ±3 cm−1.
Optical Study of Copper Diffusion in Cadmium Sulfide Single Crystals
Authors: Szeto Whalun , Somorjai G. A. 
Published: January 2005

The diffusion of copper in cadmium sulfide single crystals has been studied by optical transmission in the temperature range 500°—700°C. Diffusion was made parallel to the c axis. The intensity of the monochromatic light beam (λ=5230–20 Å) transmitted through a small section of the sample was monitored along the diffusion profile. The relationship between the light transmission T and the penetration distance x has been derived and applied to the geometry employed in the experiments. From the slope of the plot lnln (1/T) vs x2, the diffusion coefficient has been determined and the activation energy for the copper diffusion along the c axis has been calculated (ΔE=13.4 kcal/mole).
Light absorption by the doped crystals is primarily due to the copper acceptor centers and defects which are generated by the copper diffusion via the self-compensation mechanism. Scattering of light by copper precipitate aggregates has also been considered. The results of the several diffusion studies may be explained assuming that copper diffuses interstitially in the cadmium sulfide lattice and there is an equilibrium between interstitial and substitutional copper during the diffusion. The solubility of substitutional copper which occupies cadmium sites must be greater than the solubility of copper interstitials. The results of the optical studies of copper diffusion compare favorably with diffusion studies using radiotracer techniques. Since it is a nondestructive method, under certain conditions it should be more useful than other types of diffusion analysis.
United-Atom Approximation Applied to Argonlike Molecules. III. HCl and SiH4
Authors: Hake R. B. , Banyard K. E. 
Published: January 2005

The united-atom approximation has been used to obtain molecular wavefunctions for HCl and SiH4 in the gaseous state. Theoretical values were determined, in each instance, for the molecular energy, bond length, force constant, molar diamagnetic susceptibility, and the coherent x-ray scattering factor. Where possible, the results were compared with the corresponding experimental data.
For SiH4, a comparison of the present results was made with the earlier work of Carter and also of Albasiny and Cooper. These workers used, respectively, a numerical Hartree self-consistent-field approach and a numerical Hartree—Fock scheme, the latter study being performed within a spherical and a nonspherical approximation. For the HCl molecule, some comparison is made with the two-center SCF—LCAO—MO calculation performed by Nesbet.
In each case, the united-atom treatment gave a molecular energy which was 98.9% of the experimental value. Other physical properties for HCl and SiH4 derived from the present model compare favorably with similar quantities obtained from the more elaborate calculations and also with the corresponding available experimental data.
Kinetic Isotope Effects in the Reaction between Atomic Chlorine and Molecular Hydrogen. Tunnel Coefficients of the Hydrogen Atom through an Asymmetric Potential Barrier
Authors: Persky Avigdor , Klein Fritz S. 
Published: January 2005

Kinetic isotope effects for the reactions between atomic chlorine and molecular hydrogen have been measured in the range of −30° to +70°C. The following expressions were obtained: RH2/HT=(1.27±0.03) exp[(797±14)/RT],RH2/D2=(1.44±0.06)exp[(1128±17)/RT],RH2/DT=1.534exp(1422/RT),RH2/T2=1.545exp(1693/RT).
The isotope effect of HD, RH2/HD=(1.24±0.03) exp[(490±6)/RT],has been redetermined and found to agree with previous measurements.
Theoretical calculations of these isotope effects, using (1) a Sato model, (2) a generalized Sato model, and (3) the Johnston—Parr method, were made to compare the calculated effects with experimental results.
Tunnel corrections were applied using (1) an asymmetric Eckart barrier, or (2) the Johnston—Rapp method with an asymmetric barrier. Best agreement (within 15%) of calculated values with experiment was obtained for a generalized Sato model including Johnston—Rapp tunnel corrections. Empirical sets of four force constants describing the transition state H–H–Cl are also given. These are used to calculate isotope effects which are in excellent agreement with experimental values.
EPR in Selenium
Authors: Sampath P. I. 
Published: January 2005

EPR studies at X-band frequencies have been carried out between 300° and 77°K on amorphous and crystalline selenium. Dominating the spectra of the amorphous material were a large number of paramagnetic centers ∼1019/cc which contribute to an unusually broad and inhomogeneous line of width, ΔHp p∼3Kg and g=2.3 to 2.8±0.01. The linewidths and g values were very sensitive to heat treatments. This broad line is attributed to electrons at chain ends in a highly disordered region of the solid. A different species was also present in much lower concentrations ∼1013/cc, as observed by a sharp resonance with peak-to-peak linewidth, ΔHp p∼6 G and g=2.0039±0.0006, which is close to the g value of 2.0023 for a free electron. Heat treatments altered the magnitude of the signal in an erratic manner and up to ∼1016/cc spins were observed with no changes in ΔHp p or g value. The identification is rather uncertain. Theoretical considerations of the g value and linewidth favor a center associated with an impurity (i.e., oxygen) at the end of the selenium chain but have shown that a chain end interacting with a neighboring chain cannot be ruled out. Experimental results tending to minimize the role of oxygen were that no conclusive differences were observed when samples were heat treated in air or vacuum or prepared by evaporation, and the appearance of a virtually identical resonance when single crystals of hexagonal selenium were damaged (mechanically and by electron bombardment).
No resonances were found in pure ``as grown'' monoclinic or hexagonal selenium. This result was unexpected for the latter material, and chemisorption of oxygen on the surface is thought to be the explanation.
Study of Inelastic Collisions by Drifting Ions
Authors: Kaneko Y. , Megill L. R. , Hasted J. B. 
Published: January 2005

A series of experiments has been performed in which a mass-analyzed ion beam is injected into a drift tube containing gas. The ions drift through the tube under the action of a uniform electric field and they undergo inelastic processes. The product ions are mass analyzed upon exit. The drift velocity and the ratio of the primary and secondary ion currents are measured as a function of the electric field and the gas pressure in the drift tube. From these data the cross section of the process is calculated. The effect of the lateral diffusion in the drift tube is discussed theoretically.
Cross sections are determined in the energy range from 0.06 to 10 eV for the processes, Ne++Ar→Ne+Ar+,Ar++Ne→Ar+Ne+,O++N2→O+N2+,O++O2→O+O2+.Because of the nature of the ion source used these processes are supposed to be conducted largely by the ions in their excited states. It is shown that the cross sections of the former two processes agree well with predictions based on the theory of Rapp and Francis if appropriate combinations of excited states are assumed. At the high-energy end, the cross sections of the latter two processes agree well with the results of the beam experiment of Stebbings et al. At the low-energy end, the cross section of the last process agrees well with experimental result of Fehsenfeld et al. at room temperature. A remarkable minimum is found in the last process.
Gas-Phase Electron Resonance Spectra of Fluorine and Chlorine Atoms in Their Ground (P322) and Excited (2P½) Electronic States
Authors: Carrington Alan , Levy Donald H. , Miller Terry A. 
Published: January 2005

The gas-phase electron resonance spectra of fluorine and chlorine atoms in their ground (P322) and excited (2P½) states are described. Fluorine atoms are formed by passing CF4 through a microwave discharge; the P322 spectrum shows six strong lines and five weaker lines, three of the latter being previously unreported and arising from ΔMF=0 transitions. Two lines of the 2P½ spectrum are detected and their intensity relative to that of the ground-state spectrum indicates a non-Boltzmann distribution between the P322 and 2P½ states.
Chlorine atoms are formed by passing CF3Cl or CF3Cl/Cl2 mixtures through a microwave discharge. In addition to the intense 35Cl and 37Cl P322 spectra, four weak lines arising from excited 35Cl 2P½ atoms are detected. The intensities of these lines also indicate a non-Boltzmann distribution between the ground and excited states.
ESR Absorption Spectra of Two Phosphorous Defect Centers in Irradiated Single-Crystal Calcite
Authors: Serway R. A. , Marshall S. A. 
Published: January 2005

Two paramagnetic defect centers associated with phosphorous impurities and corresponding to S=½ and I=½ have been observed in irradiated single-crystal calcite. One center, which is produced by γ irradiation, has an ESR absorption spectrum which consists of six doublets at 77°K and below, each exhibiting orthorhombic symmetry with spin-Hamiltonian parameters given by gxx=2.0072, gyy=2.0033, gzz=2.0122, Axx=52.53 Mc/sec, Ayy=56.16 Mc/sec, and Azz=52.21 Mc/sec, where the relation between the x, y, z coordinates and those of calcite is discussed. As the temperature is raised, the lines of this spectrum are observed to broaden and at about 150°K the spectrum collapses into one doublet pattern which exhibits symmetry about the calcite (111) direction suggesting that the coordinates of the defect center undergo some form of motion whose mean z axis is parallel to the calcite (111) direction. This behavior is attributed to thermally induced reorientations of the defect between six magnetically inequivalent sites. The activation energy for this reorientation is estimated to be 0.10 eV from low-temperature line-broadening data. An electron—nucleus double-resonance absorption spectrum observed at 4.2°K has demonstrated the doublet to be associated with 31P. It is concluded that the center giving rise to this ESR spectrum is the PO42− molecule—ion.
The second defect center is produced by neutron irradiation and has an ESR absorption spectrum consisting of a doublet pattern which exhibits symmetry about the calcite (111) direction. This center is stable up to about 300°K and at 77°K has spin-Hamiltonian parameters given by g∥=2.00165, g⊥=2.00162, A∥=2293.2 Mc/sec, A⊥=1789.6 Mc/sec, and gnβn/gβ=−0.000608. This spectrum is identified with the PO32− molecule—ion which is believed to occur as a substitution for the carbonate ion.
Potential Function for the Inversion Process of Ammonia
Authors: Moccia R. , Randaccio L. 
Published: January 2005

The process of inversion of ammonia has been considered as described by two totally symmetric internal coordinates.
The potential function has been chosen by theoretical considerations and the values of the parameters which appear in it have been fixed by minimizing the differences between the calculated eigenvalues of the vibrational problem and the known values of the observed frequencies. Two versions of the vibrational problem have been considered; a simplified one (monodimensional), where only the bond angles are allowed to change, and a complete two-dimensional one where the bond lengths were also allowed to change.
The potential functions so obtained give a fairly good agreement between calculated and observed frequencies. The two-dimensional potential function has the minimum at a bond length of 1.878 a.u. and at a bond angle of 105°36′ and gives a value of 0.00905 a.u. as the potential barrier to inversion. The bond length for the minimum of energy at the planar configuration is 1.837 a.u.
This potential function and the resulting eigenfunctions of the vibrational Hamiltonian have been employed to calculate some spectroscopic constants, such as the quadratic and cubic force constants related to two totally symmetric coordinates, and the differences between the rotational constants of the odd and the even levels. The agreement with the available experimental data is satisfactory. Results of the above calculations are also given for ND3.
Time-Dependent Behavior of Activated Molecules. High-Pressure Unimolecular Rate Constant and Mass Spectra
Authors: Mies F. H. , Krauss M. 
Published: January 2005

A quantum-mechanical theory of the unimolecular decay of metastable or activated molecules is developed using Fano's treatment of resonance scattering. A resonance state is synonymous with the so-called activated molecule in unimolecular kinetics, and a set of widths is associated with each state which is a measure of the coupling to the various dissociation continuum channels (each channel designates an ``activated complex''). If the widths are small compared to the spacings between those neighboring states which are coupled to the same continua, then an ensemble of molecules prepared in a given activated state will decay exponentially in time, as a radiating or autoionizing excited atomic state does. However, unimolecular decay is fundamentally a problem in ``overlapping'' resonance widths, and is best considered using Fano's theory, which incorporates proper treatment of the overlap. This paper is particularly concerned with the implications of overlapping widths on the high-pressure rate constant, and on mass spectra.
There are two effects of overlapping which are most striking. First, the time decay of an ensemble of metastable molecules is no longer a pure exponential, but for the special cases considered is represented by a sum of exponential, oscillatory, and/or linear terms; this can affect the interpretation of mass spectra. Second, the high-pressure rate constant is related to the initial rate of decay of a canonical ensemble of activated molecules, and proper consideration of overlap imposes an upper bound on the rate of dissociation without any artificially imposed restrictions on the widths. This bound yields the ``universal rate constant,'' kT/h times a transmission coefficient which is a function of the widths and spacings of the activated molecules, and has an upper limit of 1.
Reactions of Nitrogen—Hydrogen Radicals. II. Decomposition of Hydrazine by Hydrogen Atoms
Authors: Ghosh Pradip K. , Bair Edward J. 
Published: January 2005

The luminescent reaction of hydrazine with atomic hydrogen was studied in flowing gas systems. The emission is due to NH2 radicals apparently produced by the process N2H4+H→NH3+NH2(2A1)* . Estimates of the emission quantum yield show that this is a relatively minor process. Accepting the conclusion of Schiavello and Volpi that the major decomposition process is N2H4+H→N2H3+H2 with a rate, 3.5×108 exp (−2000/RT) liters/mole·sec, the temperature dependence of the emission intensity is interpreted in terms of these competing processes to give a rate 1.2×105 exp (−2600/RT) liters/mole·sec for the emission reaction. The emission spectrum appears to have a short wavelength limit corresponding to 50.7 kcal, yielding a value for the heat of formation of NH2 consistent with other determinations.
The absorption spectrum shows an unexpectedly high concentration of NH2 radicals in the reaction zone. This is consistent with the other known facts if the process, N2H3+H→2NH2, becomes important when the [H]/[N2H4] ratio is large.
Absorption Spectra of Gaseous NdBr3 and NdI3
Authors: Gruen D. M. , DeKock C. W. 
Published: January 2005

Absorption spectra have been obtained of gaseous NdBr3 and NdI3 in the range 4000–25 000 cm−1 between 1000° and 1200°C. Spectra of solid and liquid NdI3 near the melting point have also been measured.
The most prominent feature of the gaseous spectra is a complex band located between 16 000–17 000 cm−1 with oscillator strengths of 3.3×10−4 and 5.3×10−4 for NdBr3 and NdI3, respectively. The band is assigned to the hypersensitive transition 4I9/2—4G5/2.
The oscillator strength of this transition in the vapor molecules is 10–50 times greater than in the solution systems studied by Carnall, Fields, and Wybourne. Various intensity mechanisms are discussed and it is concluded that the vibronic mechanism gives order-of-magnitude agreement with results. Judd's proposal that the parameter T2 is particularly sensitive to environment is borne out by the results on the vapor spectra.
Photoionization of n-Butane at 1067–1048 Å. Decomposition of the Parent Ion and Superexcited Molecule
Authors: Ausloos P. , Lias Sharon G. 
Published: January 2005

n-C4H10, n-C4D10, CD3CH2CH2CD3, and C4D10—C3H6 mixtures have been irradiated in the presence of oxygen with the argon resonance lines at 1067 and 1048 Å. On the basis of saturation-ion-current measurements, the ionization-efficiency ratios ηC4D10/ηNO and ηC4H10/ηNO were estimated to be 0.480±0.005 and 0.465±0.005, respectively. It is demonstrated that at the argon-resonance lines the C4H10+ ion undergoes fragmentation according to the following two processes: C4H10+→C3H7++CH3→C3H6++CH4.The isotopic analysis of the propane fraction formed in the irradiation of n-C4H10–n-C4D10–O2 mixtures indicates that the propyl ion which reacts with n-butane to form propane by a H− or D− ion transfer has the sec-propyl ion structure. It is further shown that, in agreement with recent studies on ion—molecule reactions, the C3H6+ ion also reacts with C4H10 to form C3H8 (H2− transfer). The yield of the parent ion was estimated by making use of the recently established H2-transfer reaction: C4H10++C3D6→CD3CDHCD2H+C4H8+.
The fragmentation of the butane parent ion is strongly quenched by an increase in the pressure of butane, or upon addition of an inert gas. The following approximate relative efficiencies for the quenching of the fragmentation of the excited C4D10+ ion are obtained: He, 1; N2, 5; C4D10, 35. It is also noted that the fragmentation of the C4D10+ ion is more readily quenched by collision with He than that of the C4H10+ ion by about a factor of 5.
The fragmentation of the neutral excited molecule has been examined briefly on the basis of the isotopic analysis of products formed in the photolysis of CD3CH2CH2CD3—O2 mixtures at 1470, 1236, and 1067–1048 Å, and of those formed in the photolysis of C4D10—H2S mixtures at 1236 Å. It is concluded that the modes of decomposition of the superexcited molecule are essentially identical to those observed for molecules excited at photon energies below the ionization energy, although the elimination of an H2 molecule or an alkane may be of lesser importance at the shorter wavelength.
Mathematical Properties of Frost's Local-Energy Method
Authors: Stanton Richard E. , Taylor Robert L. 
Published: January 2005

Frost's local-energy method is analyzed in two different ways. An exact, trigonometric solution is carried out for the two-dimensional problem. The more general problem is treated by perturbation theory.
It is shown that not all solutions of the local-energy equations correspond to minimum variance. Some correspond to maximum variance, others to a saddle point on the variance hypersurface. The number of minimum variance solutions is equal to the number of basis functions when the latter are well chosen, but may otherwise be smaller.
Development of a High-Pressure Capillary-Tube Viscometer and Its Application to Methane, Propane, and Their Mixtures in the Gaseous and Liquid Regions
Authors: Giddings John G. , Kao James T. F. , Kobayashi Riki 
Published: January 2005

A versatile absolute capillary-tube viscometer has been developed and applied to measure the viscosity of methane, propane, and four selected mixtures of the two from 100 (6.8 atm) to 8000 psia (544.4 atm) and temperatures from 40° (4.44°C) to 280°F (137.78°C). The reproducibility of the data, excluding the critical regions, was 0.25%. The data for the pure components are critically compared with values available in the literature.
Within the experimental limits of this study, it has been found that, for each pure component and mixture studied, the residual viscosity, the viscosity at some pressure and temperature less the dilute-gas viscosity at that temperature, is a unique and continuous function of the density.