bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absorption Spectra of Polyatomic Molecules at High Temperatures. II. Benzene and Perfluorobenzene. Kinetics of the Pyrolysis of Benzene
Authors: Bauer S. H. , Aten C. F. 
Published: January 2005

The near-ultraviolet absorption spectra of benzene and of hexafluorobenzene vapors were measured over the range 690° to 1900°K. The samples were diluted with argon (90%—99% of inert gas) and shock heated. Absorption coefficients were evaluated at a fixed frequency (Hg, λ2537) as a function of time after passage of the shock front [Iλ(t)], and as a function of wavelength at a fixed time interval [Iτ(λ)]. For temperatures below 1300°K for C6H6 and 1600°K for C6F6, absorptions were recorded prior to the occurrence of significant decomposition of the sample; above these temperatures values were deduced for benzene from measurements extrapolated to zero time.
Integrated absorption coefficients (f) for the 1B2u←1A1g transition were evaluated for the range in temperature given above and were compared with theoretical analyses of the effect of temperature on f numbers.
A mechanism for the pyrolysis of benzene is proposed which is compatible with flow experiments through tubes at 1500°K and the present shock-tube data.
Trapping and Energy Transfer in Atomic Collisions with a Crystal Surface. II. Impurities
Authors: McCarroll Bruce 
Published: January 2005

The influence of surface impurities and internal impurities on (1) atomic condensation on a solid, (2) equilibration of the newly captured atom with the solid, and (3) the accommodation coefficient, are examined through calculations with a one-dimensional semi-infinite analog in the harmonic approximation. The general equation for the semi-infinite lattice (arbitrary composition) and impinging gas atom are specialized to (1) a pure lattice with a surface impurity (variable mass and bonding) and (2) a pure lattice with a defective third atom (variable mass and bonding).
For the surface impurity: a decrease in coupling K1 decreases the condensation efficiency. Decreasing either the mass M1 or K1 decreases the rate of thermalization of a captured atom. There is a maximum in the condensation efficiency when M1 is varied. Light surface atoms do increase the accommodation coefficient.
For the internal impurity: a weakening of impurity bonding decreases both trapping efficiency and rate of thermalization. Light impurities decrease the condensation efficiency, but increase the thermalization rate. The effect of the internal impurity on the accommodation coefficient is negligible.
Analysis of the Electronic Spectra of Neodymium Ethylsulfate
Authors: Gruber John B. , Satten Robert A. 
Published: January 2005

The polarized absorption spectra of single crystals of neodymium ethylsulfate [Nd(C2H5SO4)3·9H2O] have been studied between 11 000 cm—1 and 28 500 cm—1 at 77° and at 4.2°K. From the 77°K polarized absorption spectrum of crystals of different thicknesses, it is possible to identify transitions from all the Stark components of the ground level 4I9/2 to many of the Stark components of excited SLJ levels of the 4f3 configuration. The electronic transitions particularly of the 4I9/2 ground level are reliably singled out from among vibronic transitions. The experimental assignment based on selection rules and the number of transitions observed is further verified by a comparison of the experimental levels with the ``free-ion'' spectrum predicted on the basis of the parameters F2=331.33 cm—1, F4=47.956 cm—1, F6=5.313 cm—1, and ζ=880.11 cm—1.
A first-order crystalline-field splitting calculation based on the parameters B20=58.4 cm—1, B40=—68.2 cm—1, B60=—42.7 cm—1, and B66=595 cm—1 gives a predicted splitting to within a mean deviation of 4 cm—1.
Photolysis of Aqueous Nitrite Solution Containing Mercuric Salts
Authors: Shinohara Kenichi , Shida Tadamasa , Saito Nobufusa 
Published: January 2005

Photolysis of aqueous sodium nitrite plus mercuric salt solutions has been studied with a high-pressure mercury lamp. The irradiation of mercuric salt solution does not give any noticeable amount of mercurous salt whereas the admixture of sodium nitrite and mercuric salt does.
Two possible explanations are suggested for the reduction of mercuric salt; one is that the absorption of light quantum by nitrite ions induces electron transfer from the ions to water molecules in the hydration shell and that the expanded electron of the excited ions reduce mercuric to mercurous. An alternative is that nitrite ions are excited to their low-lying electronic states in which they can reduce mercuric salts directly.
Raman Spectral Studies of Aqueous Solutions of Selenic Acid
Authors: Walrafen G. E. 
Published: January 2005

Relative integrated Raman intensities of aqueous solutions of selenic acid have provided concentrations of the species H2SeO4, HSeO4—, and SeO42—. When water is added to supercooled selenic acid at 25°C, the molecular H2SeO4 concentration, [H2SeO4], which is approximately 18 mole liter—1 in the pure acid, decreases rapidly and approaches zero, as the stoichiometric concentration of selenic acid, CH2SeO4, approaches 11–12M. Simultaneously, the HSeO4— concentration, [HSeO4—], increases, but it falls below the stoichiometric water molarity CH2O as dilution progresses. When CH2SeO4 = CH2O = 14.5M, [HSeO4—]&lt;CH2O, indicating that the reaction H2SeO4+H2O = HSeO4—+OH3+ is incomplete. With further dilution, [HSeO4—] attains a maximum value of about 12.9 mole liter—1, at CH2SeO4 = 13.5M, and near CH2SeO4 = 11–12M, where [H2SeO4]≈0, the absence of intense characteristic Raman lines of SeO42— indicates that [H2SeO4—]≈[OH3+]. Below CH2SeO4 = 11–12M, Raman lines of SeO42— appear, as [HSeO4—] continues to decrease. When CH2SeO4 has decreased to approximately 4.2M, [SeO42—] attains a maximum value of about 0.91 mole liter—1, and the concentration at which [SeO42—] is maximal, compares favorably with the concentration corresponding to a maximum in the electrical conductivity, CH2SeO4 = 3.7M.
Fundamental vibrational frequencies of H2SeO4, HSeO4—, and SeO42— have been assigned according to structures of C2v, Cs, and Td symmetry, respectively, and those assignments are compared with vibrational assignments of the closely related species H2SO4, HSO4—, and SO42—. Other comparisons between Raman spectra of nearly pure selenic and sulfuric acids, however, reveal additional frequencies at 932 and ∼1200 cm—1, respectively, produced by intermolecular vibrations. Such additional vibrations suggest the existence of extended, strongly hydrogen-bonded networks, in which symmetric vibrations of the SeO2 or SO2 groups of individual H2SeO4 or H2SO4 molecules are out-of-phase in neighboring molecules. In addition, another frequency of aqueous solutions of selenic acid at ∼800 cm—1, obtained from careful analysis of band contours, presumably is also produced by intermolecular vibrations between OH3+ and HSeO4—, in accordance with the low electrical conductivity and the high viscosity of solutions in which those ions are predominant.
On the Kinetic Theory of Dense Fluids. XIV. Experimental and Theoretical Studies of Thermal Conductivity in Liquid Ar, Kr, Xe, and CH4
Authors: Ikenberry Lynn D. , Rice Stuart A. 
Published: January 2005

In this paper we report experimental and theoretical studies of the thermal conductivity of liquid Ar, Kr, Xe, and CH4, in the temperature range 90°—235°K and the pressure range 1–500 atm. It is found that: (a) The magnitude, the temperature dependence, and the pressure dependence of the thermal conductivity all decrease in the following order: CH4, Ar, Kr, Xe. (b) The gross behavior of the coefficient of thermal conductivity is the inverse of the behavior of the self-diffusion coefficient: κ increases (whereas D decreases) as the pressure increases along an isotherm and κ decreases (whereas D increases) as the temperature increases along an isobar. (c) The statistical theory of Rice and Allnatt leads to easily interpreted analytic formulas for the coefficient of thermal conductivity. (d) The theory of Rice and Allnatt leads to predictions in quantitative agreement with experiment.
The importance of accurate pair correlation functions, the relative roles of strong repulsive and soft attractive potentials, and implications of the Rice—Allnatt theory are briefly discussed.
Internal Conversion from Upper Electronic States to the First Excited Singlet State of Benzene, Toluene, p-Xylene, and Mesitylene
Authors: Braun Charles L. , Kato Shunji , Lipsky Sanford 
Published: January 2005

The variation with excitation wavelength of the fluorescence efficiencies of some alkyl benzenes has been studied from 2700 to 1600 Å. Measurements have been made in both liquid (pure and dilute solution) and vapor phases. For pure liquids the internal conversion efficiency βλ from upper electronic states to the first excited singlet state has been found to be significantly less than unity and to increase in the order benzene, toluene, p-xylene, mesitylene when comparisons of βλ are made at comparable excitation wavelengths. Solvent effects on βλ have been noted. No emission is observed from any alkyl benzene studied in the vapor phase for excitations beginning on the long-wavelength side of the second absorption band and extending to shorter wavelengths.
Dissociation, internal conversion to the ground state, and intersystem crossing to a triplet state are considered as mechanisms for the disappearance of the upper electronic singlet states. Measurements of the benzene-sensitized phosphorescence of biacetyl indicate that if the disappearance mechanism involves upper-level intersystem crossing to the triplet manifold, then the triplets so produced do not efficiently internally convert to the lowest triplet state.
Rate of Exchange of Halide Nuclei with Mercury (II) in Aqueous Solution
Authors: O'Reilly D. E. , Schacher G. E. , Schug K. 
Published: January 2005

Linewidths ΔHms of the I127 nuclear magnetic resonance of water solutions of KI in the presence of varying amounts of HgII have been measured at temperatures in the range 273° to 373°K. At constant [I—], ΔHms depends linearly on the concentration of HgII: ΔHms=kms[HgII], where kms ranges from 1.9×103 G M—1 at [I—]=4.0M to 3.7×105 G M—1 at [I—]=0.005M (300°K). By means of the modified Bloch equations the results may be interpreted as due to a rapid exchange of iodine nuclei among the species I—, HgI42—, and HgI3(OH2)—. Broadening of the I127 nuclear magnetic resonance is produced by relatively short relaxation times of I127 in the mercury complexes; T2(I—)=1.7×10—4 sec, T2(HgI42—)=1.1×10—7 sec (300°K). Biomolecular rate constants for the following exchange reactions have been obtained: HgI42−+I−→ lim k1I−+HgI42−,HgI3(OH2)−+I−→ lim k2I−+HgI3(OH2)−,HgI3(OH2)−+I−→ lim k3H2O+HgI42−.At 300°K, k1=8.8×107M—1 sec—1, k2=5.7×109M—1 sec—1, and k3=7.1×108M—1 sec—1, ΔE1‡=1.8±0.6 kcal mole—1.
The rates appear to be diffusion limited and may be interpreted by an appropriate solution of the Smoluchowski diffusion equation. Similar but less extensive measurements have been made on KBr solutions containing added HgBr2. Again exchange appears to be diffusion controlled and T2(HgBr42—) is much shorter than T2(Br—).
The relatively small value of k1 is attributed to a negative entropy of activation associated with dielectric polarization of the solvent by the ions involved.
The observed relaxation rate of I127 in HgI42— combined with an estimate of the quadrupolar coupling constant of I127 in solid K2HgI4 allows an estimation of the rotational correlation time τc of HgI42— in solution, which at 25°C is equal to 1.4×10—11 sec. This time is a factor of six shorter than estimated from the Debye expression for τc.
Transpiration and Mass Spectrometric Studies of Equilibria Involving BOF(g) and (BOF)3(g)
Authors: Hildenbrand Donald L. , Theard Lowell P. , Saul Albert M. 
Published: January 2005

The reaction of BF3(g) with B2O3(l) was studied by the transpiration method in the temperature range 600° to 1100°K. Results indicate the reaction to be BF3(g)+B2O3(l)=(BOF)3(g).ΔH298° was found to be 4.2 kcal, and leads to ΔHf298°=—566.8±1 kcal/mole for (BOF)3(g).
The vapor above mixtures of MgF2 and B2O3 contained in a Knudsen cell was analyzed with a mass spectrometer and was found to contain BF3(g), (BOF)3(g), and BOF(g) in the range 980° to 1230°K. From studies of the temperature dependence of appropriate ion intensities the heat of the reaction (BOF)3(g)=3BOF(g)was derived as 131 kcal at 1125°K. Use of low ionizing electron energies was required to avoid fragmentation effects. The heat of formation of BOF(g) at 298°K was calculated to be —144±3 kcal/mole.
NMR Study of the Protolysis Kinetics in Simple Amino Acids. II. Sarcosine (the Zwitterion Form)
Authors: Sheinblatt M. 
Published: January 2005

The mean lifetime of the amino group τ of aqueous solutions of sarcosine in the zwitterion form was measured using the NMR technique at 21°±1°C. The zwitterion can participate in the following exchange reactions: CH3NH2+CH2COO−+H2O⇌ lim kICH3NHCH2COO−+H3+O,CH3NH2+CH2COO−+OH−⇌ lim kIICH3NHCH2COO−+H2O,CH3NH2+CH2COO−⇌ lim kIIICH3NHCH2COOH (intramolecular),CH3NH2+CH2COO−+CH3NH2+CH2COO−⇌ lim kIVCH3NHCH2COO−+CH3NH2+CH2COOH (intermolecular),CH3NH2+CH2COO−+CH3NHCH2COO−⇌ lim kVCH3NHCH2COO−+CH3NH2+CH2COO−,CH3NH2+CH2COO−+CH3NHCH2COOH⇌ lim kVICH3NHCH2COO−+CH3NH2+CH2COOH.From the experimental results, i.e., the dependence of 1/τ on 1/aH+ and the concentration of the amino acids, the following rate constants were determined: kV=1,5×108 (sec−1 M−1),  kII=4×1010 (sec−1 M−1),kI[H2O]+kIII=80 (sec−1),and kIV+(kVI/K4)=145 (sec−1 M−1).
Discussing and comparing the above rate constants with the rate constants for similar reactions enables one to estimate the value of each of the rate constants given as a sum.
NMR Shift and Diffusion Study of Electrolytes in 50% Dioxane—Water Mixtures
Authors: Fratiello Anthony , Douglass Dean C. 
Published: January 2005

High-resolution chemical shift measurements were carried out on electrolytic solutions in 50% dioxane—water mixtures. Whereas the water proton resonance position was displaced significantly by the addition of electrolyte, the dioxane signal in all mixtures remained unperturbed. Further, the results, particularly those obtained with chloride solutions of the small or highly charged Be, La, and Th ions indicated that strong selective solvation of cations by the water was occurring. This conclusion was substantiated by differences in the dioxane and the water linewidths observed in several solutions, including those of paramagnetic salts.
Self-diffusion coefficients of dioxane in these electrolytic mixtures were also measured by the nuclear magnetic resonance spin-echo technique. The observed diffusion data could be interpreted solely on a hydrodynamical basis, again indicating that no significant interaction was occurring between dioxane and the added electrolyte.
Absolute Infrared Intensities of Vibration Bands in Ammonia and Phosphine
Authors: McKean D. C. , Schatz P. N. 
Published: January 2005

The absolute absorption intensities of the fundamental vibration bands in ammonia and phosphine have been measured. Normal coordinates are calculated for each of the vibrations and the intensities interpreted in terms of bond moments μ and their derivatives ∂μ/∂r.
Values of ∂μ/∂r for the NH and PH bonds in the A1 mode are 0.6 and 1.2 D/A, respectively; in the E mode the corresponding values are 0.2 and 0.8 D/A.
Values of the vibrational bond moments found are 1.0 D (A1) and 0.5 D (E) for the NH bond; 0.7 or 0.5 D (A1) and 1.2 or 0.6 D (E) for the PH bond.
The relation of these vibrational bond moments to the molecular dipole moment and the moment (μu.p.) of the unshared pair of electrons is discussed in detail. After corrections have been applied for changes in magnitude and direction of μu.p. during the vibrations, the results for NH3 are compatible with the following static moments: μNH∼0.7D(H+),μu.p.∼0.7D.The data for PH3 are less internally consistent. ``Likely'' moments, taken from the A1 bending vibration, are μPH∼0.2(H+),  μu.p.∼0.2D.
Electronic and Vibrational States of Azulene
Authors: Sidman Jerome W. , McClure Donald S. 
Published: January 2005

The absorption and emission spectra of azulene have been studied in a substitutional solid solution in napthalene at 20°K. The spectra are polarized and are very sharp, and from the polarization properties of the absorption transitions it has been determined that the first excited state at 14 652 cm—1 is Lb, 1B1 [we will designate an electronic state by giving first the Platt symbol (J. R. Platt, J. Chem. Phys. 17, 484 (1949) and then the C2v group symbol, Herzberg, Infrared and Raman Spectra of Polyatomic Molecules (D. Van Nostrand Company, Inc., New York, 1945)] (the transition with the ground state is transversally polarized), whereas the second excited state at 28 050 cm—1 is La, 1A1 (the transition with the ground state is long-axis polarized), in agreement with the theoretical predictions of Platt and Moffitt. Vibrational analyses have been performed for the two absorption transitions, and the second transition appears to be perturbed by vibrational-electronic interaction.
A sensitized emission spectrum has also been found, in which excitation of the napthalene leads to emission from the second excited state of azulene to the ground state. A vibrational analysis of the emission transition yields ground state vibrational frequencies which are in excellent agreement with the vibrations deduced from the infrared absorption spectrum.
Environmental effects are discussed, and an attempt is made to correlate the vibrations in the different electronic states.
Electronic Spectra of Cyclo-Octatetraene, Tetraphenylene, and s-Dibenzcyclo-Octatetraene
Authors: McEwen K. Lenore , Longuet-Higgins H. C. 
Published: January 2005

The electronic transition energies of cyclo-octatetraene, tetraphenylene and s-dibenzcyclo-octatetraene have been calculated by treating each molecule as four separate π-electron subsystems, the excited configurations of which interact under the influence of the Hamiltonian for the complete system.
The calculated transition energies for cyclo-octatetraene and tetraphenylene are in good agreement with experimental data, while the calculations for s-dibenzcyclo-octatetraene suggest that the absorption data for this compound is in error.
Homogeneous Exchange Reaction Between Hydrogen and Deuterium
Authors: Boato G. , Careri G. , Cimino A. , Molinari E. , Volpi G. G. 
Published: January 2005

The homogeneous exchange reaction between hydrogen and deuterium has been reinvestigated, to see whether a more satisfactory quantitative test of the transition state method could be obtained in this simple chemical reaction.
The reaction was studied in the temperature range from 916°K to 1010°K, where the heterogeneous contribution from the walls was found to be negligible. Preventing air from diffusing into the reaction vessel trough the walls, exchange rates lower by a factor of 2.0 than those obtained by previous authors were found in the whole temperature interval. The total activation energy was determined as 59.8±0.4 kcal/mole.
The validity of the transition state method was tested by extrapolation of the experimental data to a lower temperature region (283°—373°K) where independent experimental data were available. Comparison of the extrapolated values with the experimental ones leads to a very good agreement.
Infrared Absorption Intensities and Bond Moments in BF3 and Related Molecules
Authors: McKean D. C. 
Published: January 2005

The infrared absorption intensities of the fundamental vibration bands of BF3 have been measured and vibrational bond moments μ and their derivatives ∂μ/∂r determined. In the A2″ class, μBF=1.7 D; in the E′ class μBF=0.9 or 2.6 D, ∂μ/∂r = —6.1 or +4.0 D/A.
Inspection of the form of the bending modes suggests that deviations from the bond moment approximation occur such that μ(A2″) &lt;μ(static) &lt;μ(E′). The solution μ(E′) = 2.6 D is therefore preferred.
Re-examination of the data of Schatz and Hornig on CF4, SiF4, and SF6 in the light of the present results shows that the vibrational bond moments in these molecules are: μCF∼2.4, μSiF∼3.3, μSF∼2.7 D. These moments are roughly equal to Δr0, where r0 is the bond length and Δ the electronegativity difference between the atoms in the bond.
The available data on μ and ∂μ/∂r for the C–F bond in various molecules are compared and briefly discussed.
Effects of a Concentration Dependence of the Sedimentation Coefficient in Velocity Ultracentrifugation
Authors: Fujita Hiroshi 
Published: January 2005

The Lamm differential equation for the sedimentation process in the ultracentrifuge is solved in closed form for the case in which the sedimentation coefficient, s, decreases linearly with the concentration, C, by employing the assumption which was adopted originally by Faxén who considered a similar problem with s independent of C.
It is shown that, with increasing concentration dependence of s, the concentration gradient curve is markedly sharpened, and the whole curve is also noticeably shifted towards the solvent side, but symmetry of the curve is practically maintained except at the edges.
A simple and approximate equation which predicts the position of the maximum of a given boundary curve as a function of time for a given set of the parameters is derived. It is shown that this equation is useful for evaluating the sedimentation coefficient at a given concentration. An equation which also predicts the maximum height of the boundary curve as functions of time and related parameters with a satisfactory degree of approximation is obtained. Using this equation, reliable values of the diffusion coefficient may be obtained from sedimentation experiments when s depends linearly on C.
Proton Jumps and the Electrical Behavior of Ice and Ice-NH4F Solutions
Authors: Zaromb Sol 
Published: January 2005

Previous suggestions that dielectric relaxation in ice may occur by means of proton shifts have been refuted by Bjerrum. Yet, the role of ions in this relaxation process cannot be ignored in view of the more recent studies on ice-NH4F solutions, which indicate that solute ions can accelerate the rotation of ice molecules at a distance of 30 A or more from any ion.
Simple electrostatic calculations show that proton jumps in ice would entail the formation of ``Bjerrum fault sites.'' In the case of pure ice, this might explain why: (a) the proton jump conductivity is much lower than in water at 0°C; and (b) the concentration of fault sites seems to be rather high, according to Bjerrum. Estimates of the frequencies of proton jumps and of activation energies show no disagreement of the proposed explanations with known facts.
In the case of ice-NH4F solutions, proton jumps occurring between second-neighbor ion pairs, F—–H2O–NH4+, may also induce fault sites at the neighboring molecules. This ion-pair mechanism would agree with the low activation energy for these rates and with the peculiar concentration dependence of the frequency factor.
Finally, the thickness of the ion atmosphere should, at equilibrium, be less in ice-NH4F solutions than in aqueous solutions of the same concentration. This, together with the above, might account for the changes with time in the dielectric relaxation rates of concentrated ice-NH4F solutions observed immediately after freezing.