bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rotational Analysis of Some Bands of the Triplet←Singlet Transition in Formaldehyde
Authors: Raynes W. T. 
Published: January 2005

Using the absorption frequencies measured by Robinson and DiGiorgio, a rotational analysis of the 0+←0 and 1+←0 bands of the 3A2←1A1 transition in H2CO has been performed. Each band contains a number of overlapping subbands which are themselves made up of several branches consisting of individual rotational lines. Despite the overlapping, it was found possible to give assignments to a large number of lines. All branches are q-type branches; that is, only ΔK = 0 transitions are observed. The positions of the triplet-state rotational levels relative to the lowest rotational level of the ground vibronic state were obtained with the aid of the very accurate ground-state rotational levels determined interferometrically by Parkin and Poole. These triplet-state levels were found to fit accurately the Hamiltonian proposed by Van Vleck for an asymmetric-rotor molecule in a triplet electronic state provided that further terms were added to take account of rotational distortion.
Values of the rotational constants, rotational distortion constants, and spin-interaction constants of the 3A2(0+) and 3A2(1+) states have been determined. The rotational constants for the 3A2(1+) state are as follows: A = 8.6275 (±0.0008) cm−1; B = 1.1491 (±0.0001) cm−1; and C = 1.0343 (±0.0001) cm−1. The results for the 3A2(0+) state are very similar. From these constants it is possible to show that the equilibrium nuclear geometry of formaldehyde in this state is highly nonplanar, the geometrical parameters having the following values: r(C–H) = 1.10 Å; r(C–O) = 1.28 Å; ∠HCH = 118°; out-of-plane angle = 36°. The spin-interaction constants, which determine the extent of the triplet splitting of the rotational levels, take account not only of spin—molecular rotation, spin—orbit, spin—other-orbit, and spin—spin interactions, but also of the effect of rotational asymmetry upon these interactions. The observed relative intensities of the rotational lines agree very well with those predicted by the recent theory of Hougen. In particular, the almost complete absence in the spectrum of transitions to the F2 component of the triplet state is understandable in the light of this theory. As a consequence of the fact that only ΔK = 0 transitions are observed (the theoretically possible ΔK = ±2 transitions were not detected), it is possible to deduce with the aid of Hougen's theory that it is a 1A1 state that, by spin—orbit coupling with the 3A2 state, permits the formally forbidden triplet←singlet bands to occur. This result is in complete agreement with the theoretical deductions of Sidman made some years ago.
Study of Triplet—Triplet Transfer by the Method of Magnetophotoselection. II. Concentration Depolarization
Authors: Siegel Seymour , Goldstein Lester 
Published: January 2005

The concentration depolarization of the spectra from Δm=±1 electron paramagnetic resonance (EPR) transitions of photoexcited naphthalene-d8 triplet-state molecules dissolved in ethanol glasses at 77°K has been studied. An analysis of the results is made in terms of triplet-state energy transfer. It is shown that the results are completely consistent with an electron exchange triplet-state energy-transfer mechanism, with the probability of transfer being the same as that found in the case of transfer between unlike molecules. However, for the self-transfer case, back transfer is important and it was included in the analysis. It was also necessary to assume in the theoretical analysis that the rate of transfer between molecules at the effective transfer distance is slow compared to the rate of relaxation of the spin magnetization.
Some preliminary evidence is presented for an appreciable solvent effect on the polarization of the 1La band of naphthalene.
Rayleigh and Brillouin Scattering in Liquids: The Landau—Placzek Ratio
Authors: Cummins Herman Z. , Gammon Robert W. 
Published: January 2005

The classical theory of light scattering in liquids leading to the Landau—Placzek ratio for the intensities of the Rayleigh and Brillouin components is reviewed. A simple modification is proposed in which the effect of dispersion is included by defining a hypersonic compressibility βshs=1/(ρvhs2), where vhs is found from the experimentally measured Brillouin shifts. Further modification is presented to account for dispersion in the electrostriction. A modification of the Landau—Placzek equation due to Fabelinskii is discussed and shown to be essentially equivalent to our equation.
The predictions of the ratios are evaluated for 11 common liquids and compared with new experimental values reported in this paper and with other values taken from the literature. It is found that in most cases the dispersion modification leads to ratios in considerably better agreement with the experimental values than does the simple Landau—Placzek equation.
We present our measurements of the ratio of the Rayleigh and Brillouin intensities obtained with an He–Ne laser light source and photoelectric detection. We discuss the experimental technique and the data-reduction procedure. The detection time constant was sufficiently short that contributions to the Rayleigh component from dust were distinguishable from true molecular scattering. The anomalously large central component for water which has been frequently reported in the literature was thus traced to residual dust contamination and was found to be less than 2% of the Brillouin-component intensity when dust was absent.
Kinetics of Rapid Reactions in Liquid Ammonia. The Ammonia—Amide Proton Exchange
Authors: Swift T. J. , Marks S. B. , Sayre W. G. 
Published: January 2005

Highly purified liquid ammonia was prepared and the proton magnetic resonance spectrum was recorded as a function of temperature from about −70° to about 35°C. The line shapes were shown to be given quantitatively by the equation derived by Pople and precise values for the nitrogen—proton coupling constant and the transition probabilities connecting the 14N spin states were measured.
The Bloch equations pertinent to pure 14NH3 were extended to include the possibility of chemical exchange and a means was devised to extract precise values for the rate constants for the exchange process.
Solutions of KNH2 in NH3 were prepared by the decomposition of potassium—ammonia solutions with platinum black and the kinetics of the ammonia—amide proton exchange were studied as a function of temperature and concentration. The bimolecular rate constant for the exchange was found to be 1.51×107 liter/mole·sec at 25°C, the enthalpy of activation is 4.0±0.5 kcal/mole, and the entropy of activation is −12±2 eu.
This large negative entropy is interpreted in terms of a sizeable reorganization of the solvent structure in the activated complex.
Thermal Conductivity of Argon in the Dense Gaseous and Liquid Regions
Authors: Rosenbaum B. M. , Oshen Steven , Thodos George 
Published: January 2005

Thermal conductivities for argon in the dense gaseous state were determined at 6.2°, 20.7°, 25.0°, and 48.8°C for pressures up to 10 340 psia, using a coaxial cylindrical cell. These values were found to be in good agreement with thermal conductivities reported by others and when expressed as residual quantities, k—k*, unique relationships resulted with ρR and the (∂PR/∂TR)ρR. These relationships were independent of temperature and pressure and included both the dense gaseous and liquid states.
The Enskog equation for the effect of pressure on thermal conductivity,k/k*=bρ[(1/bρχ)+(6/5)+0.7574bρχ],,has been applied to the data of this study and of others for the dense gaseous and liquid regions, to obtain values of b. These values were found to be independent of pressure and to depend upon temperature as follows: bρc=1.06/TR23. For these calculations, bρχ values were established from PVT data for argon. The experimental values obtained in this study were used to determine (k/ρ)min for each temperature, which were used in conjunction with the Enskog equation to produce thermal conductivities at elevated pressures. Values calculated with (k/ρ)min produced an average deviation of 1.2%, whereas the values resulting from bρc=1.06/TR23 gave an average deviation of 2.0%.
Kinetic Energies of Products of Ion—Molecule Reactions
Authors: Stanton H. E. , Wexler S. 
Published: January 2005

The mean kinetic energies of the ionic products of the reactionsC2H4++C2H4→C3H5++CH3,C2H2++C2H4→C3H3++CH3,CH3++CH4→C2H5++H2have been measured in a mass spectrometer equipped with a cylindrical electrostatic energy analyzer. The translational energies observed in the center-of-mass frame of reference for Reactions (I), (II), and (III) were 0.085±0.05, 0.150±0.05, and 0.056±0.05 eV, respectively. The values are somewhat higher than the mean kinetic energies calculated from statistical theory by two different methods (one using the ``temperature'' approximation of Chupka, the other the semiclassical approximation of Klots), but for Reactions (I) and (III) the difference was less than the experimental error. For the collision complexes formed from these primary ions and molecules, the comparisons suggest that the fractions of the excitation energies that are partitioned among the translational modes of the dissociation products of the complexes are somewhat higher than the fractions estimated from a statistical theory that assumes complete equilibration of the excess energy among the many internal degrees of freedom of the complexes.
Mathematical procedures for examining the kinematics of the ion—molecule collisions and subsequent dissociations of the complexes are described. Included are methods for eliminating the effects of instrumental bias on the experimentally determined translational energies.
Chemiluminescence in Molecular Beams. Electronic Excitation of Alkali Atoms in Exchange Reactions of Vibrationally Excited Alkali Halides
Authors: Moulton M. C. , Herschbach D. R. 
Published: January 2005

Energy transfer by a chemical-exchange process, KBr†+Na→K*+NaBr (where † denotes vibrational excitation and * electronic excitation), has been observed in a ``triple-beam'' experiment. The KBr† was formed at the intersection of crossed beams of K+Br2 and entered a second scattering chamber containing a Na cross beam, where light emitted by K* was observed with a photomultiplier behind an interference filter. The cross section for the exchange process is estimated to be at least 10 Å2. The angular variation of the light intensity agreed precisely with the angular distribution of KBr measured (by a surface-ionization detector) in the same experiment. The light disappeared when propyl iodide was substituted for Br2 (as expected, since the K+PrI reaction exothermicity is well below the threshold for electronic excitation of K). An attempt was also made to observe the nonreactive exchange process, NaBr†+K→NaBr+K* (by interchanging the K and Na beams). However, this was obscured by background light arising from collisions of K with ambient Br2; at present it can only be concluded that the cross section appears to be &lt;10% of that for the reactive exchange process.
The light yield from chemical exchange was about as large when the experiments were repeated with Br2 replaced by ICl. Thus the primary K+ICl reaction must give an appreciable yield of KCl (since the exothermicity is above the threshold for K excitation if KCl is formed but below if KI is formed). In this case, the light intensity falls off more rapidly at wide angles than the angular distribution of the alkali halide. This suggests that the primary reaction also forms KI which scatters mainly at wide angles, whereas the KCl scatters mainly forward with respect to the incident K atoms.
Hydrogen Bonding of Hydrazoic Acid in Solid Nitrogen
Authors: Pimentel George C. , Charles Stuart W. , Rosengren Kjell 
Published: January 2005

The infrared spectrum of hydrogen bonded HN3 dimers in solid nitrogen has been determined. A dimer band at 387 cm−1, assigned to the torsional distortion of the hydrogen bond, indicates the dimer has an open, not a cyclic structure. The hydrogen bond bending force constant is 0.09 mdyn/Å. The hydrogen bond frequency shift in the N–H stretching mode is 150 cm−1, which, by comparison to similar systems, suggests a hydrogen bond energy of about 2 kcal/mole.
The infrared spectrum of monomeric HN3 casts doubt upon the earlier gas-phase assignment of ν6. According to the matrix spectrum, the band center is more likely to be near 588 cm−1.
On the Nonconfirmation of the Dual Emission Properties of Biphenylene
Authors: Hochstrasser Robin M. , McAlpine Robert D. 
Published: January 2005

It is shown that the previously reported dual emission properties of biphenylene are most likely caused by an impurity that absorbs around 2800 Å, and emits fluorescence at 3000 Å and phosphorescence at 4100 Å.
The first two electronically excited states of biphenylene are discussed briefly in terms of low-temperature mixed-crystal studies in polarized light.
Ionization of Liquids by Radiation. I. Methods for Determination of Ion Mobilities and Ion Yields at Low Voltage
Authors: Hummel Andries , Allen A. O. 
Published: January 2005

Experimental methods are described in detail for determination of ion mobilities and of the zero-field conductivity induced by irradiation of insulating liquids with x rays. The yield of separated ions is thereby obtained with an accuracy of ±11% and is found to be 0.10 ion pairs per 100 eV for hexane at 23°C.
The physical processes resulting from absorption of high-energy radiation are less well understood for liquids than for gases. Though it has long been thought that most ions produced in liquids disappear immediately by initial recombination, with only a small fraction of the excitation events leading to real charge separation, no actual measurement of the yield of separated charges was available when we first undertook to make this determination (late in 1961). From the magnitude of this value for different liquids and its dependence on temperature we may hope to deduce something about the behavior of slow electrons in liquids and the geometrical distribution of the radiation-induced electric charges.
Infrared Spectra of HCl, DCl, HBr, and DBr in Solid Rare-Gas Matrices
Authors: Mann D. E. , Acquista N. , White David 
Published: January 2005

The infrared absorption spectra of HCl, H35Cl, DCl, HBr, and DBr isolated in solid rare-gas matrices in the range 4°—20°K are presented. The influence of temperature, dilution, deposition rate variations, as well as the presence of certain impurities, on the spectra are also reported and discussed.
In the fundamental region the spectra normally consist of a few relatively narrow bands or lines which show reproducible and fully reversible variation of intensity and bandwidth with change of temperature. The presence of certain dopants, e.g., N2, in the halide—noble-gas mixture leads, under suitable deposition conditions, to the replacement of the temperature-dependent features by much narrower temperature-insensitive lines at somewhat shifted frequencies.
The temperature-dependent features have been identified as individual rotation—vibration lines of the matrix-isolated diatomic molecules. Their separations are significantly less than those of the corresponding lines in the free molecule spectra, thereby indicating the existence of hindered molecular rotation in the matrix. The barrier to rotation is interpreted in terms of two different models for the molecule-lattice interactions and their limitations discussed.
The temperature-insensitive lines show no rotational structure, and are normally obtained when N2 or certain other dopants are present in the gas mixtures from which the matrices are formed at 20°K. They do not appear if the deposition is carried out at 4°K. It is suggested that the rotational quenching may be attributed to the formation of loose couples between halide and N2 molecules during the condensation process.
Microwave Spectrum, Vibration—Rotation Interaction, and Potential Function for the Ring-Puckering Vibration of Trimethylene Sulfide
Authors: Harris David O. , Harrington Howard W. , Luntz Alan C. , Gwinn William D. 
Published: January 2005

The microwave spectrum of the ground and first four excited states of the ring-puckering mode of trimethylene sulfide has been observed and assigned. From an analysis of the perturbations to the rotational spectrum arising from the coupling of the internal angular momentum with the over-all rotation of the molecule, the separation between the lowest two vibrational levels was determined to be 8229 Mc/sec. Three mixed vibration—rotation transitions have been observed, and give the more accurate value of 8232.5±0.4 Mc/sec (0.27461 cm−1) for this separation. From the vibration—rotation interaction and the relative intensities of certain lines, the potential function governing the vibration has been determined to be 7.0207Q4−87.7581Q2 cm−1, where Q is the coordinate describing the vibration. The height of the barrier to the planar configuration is 274.2±2 cm−1. The agreement between the far-infrared spectrum that was calculated using this potential function derived from microwave data, and that which was recently observed by Borgers and Strauss, is very good.
On the basis of a dynamic model for the ring-puckering motion in which the atoms move along curvilinear paths with no bond stretching, the coupling constant between the over-all rotation and the internal angular momentum was calculated. It was found to be 170 Mc/sec compared to the experimental value of 176 Mc/sec. The importance of treating the vibrational dependence of the off-diagonal elements of the inertial tensor as being equivalent to vibrational angular momentum is stressed.
Kinetics of Unimolecular Breakdown. VII. Statisticomechanical Aspects
Authors: Levine R. D. 
Published: January 2005

The concepts of statistical mechanics are examined from the point of view of application to chemical kinetics. The occurrence of a chemical reaction is considered as an example of an irreversible behavior, and is discussed as due to the combination of system dynamics and experimental conditions. The Lindemann mechanism for thermal unimolecular reactions is discussed on the basis of the relative magnitudes of the various relaxation times.
The significance of the random-phase assumption is discussed on the basis of the uncertainty relation between the occupation number and the phase. A master (Pauli) equation is derived and applied to vibrational relaxation. The construction of classical models for unimolecular fragmentation and the significance of computer simulation studies are considered.
Electron Paramagnetic Resonance and Optical Zeeman Spectra of Type II CaF2:Er3+
Authors: Rector C. W. , Pandey B. C. , Moos H. W. 
Published: January 2005

A study was made of the EPR and optical spectra of trivalent erbium in Type II crystals of calcium fluoride. The EPR spectrum disclosed the existence of cubic, tetragonal, and trigonal sites in the approximate ratios 15:20:1. The splitting values agreed with those of Ranon and Low.
The optical spectrum consisted predominantly of lines due to 〈100〉 tetragonal sites. This was established by a study of the Zeeman pattern of the lines as a function of rotation about the [1̄10] axis of the crystal. Spectra were taken over a range of 180° in increments of 5° in azimuthal angle. This provided a plot of energy versus azimuthal angle which could be used to establish the site symmetry in a purely geometric fashion.
This technique is of general applicability to problems of nonequivalent sites and provides considerably more information than Zeeman studies restricted to a few crystallographic directions. Spectral lines too weak to be followed in a rotational Zeeman study were assigned by finding ground-state splitting factors associated with their Zeeman patterns or by locating corresponding transitions from excited states of the ground Stark manifold.
For a number of lines, splitting factors were found and by consideration of the polarization of the Zeeman lines and the rotational Zeeman patterns, assignments of representations and crystal quantum numbers were made.
Flash Photolysis of H2O2 Vapor in the Presence of D2, Ar, and H218O
Authors: Greiner N. R. 
Published: January 2005

The flash photolysis of H2O2 by itself, and in the presence of D2, Ar, and H218O, was studied by the technique of kinetic absorption spectroscopy. The only observable primary products were OH(2Π½) and OH(2Π32). These ground-state levels were populated in a ratio of ∼1:1, respectively, conforming to what is observed with the halogens.
The contribution of Reaction (a) to the primary process was shown in a direct way to be no more than 20% of that of (b). Reaction (c) followed by (d) was shown to make no significant contribution to the OH concentration during the time of our experiments (&lt;200μ sec): H2O2(singlet)→ lim hνH2O(1A1)+O(1D),→2OH(2Π),→H2O(3A1)+O(3P),O(3P)+H2O2 (singlet)→OH(2Π)+HO2 (doublet),OH(2Π)+H2O2 (singlet)→H2O(1A1)+HO2 (doublet).Thus, this technique is a convenient one for directly observing reactions of OH. An upper limit to the rate constant of (e) at room temperature was determined to be 5.8±1.8×10−14 cm3 molecule−1·sec−1.
Conditions for generating vibrationally hot molecules in the primary photolytic step are discussed.
Determination of Hydrogen-Atom Concentration by Lyman-α Photometry. I. Oscillator Strength of the Hydrogen-Atom 2P,½←2S½ Transition. II. Kinetics of the Reaction of Hydrogen Atoms with Acetylene and Ethylene
Authors: Michael Joe V. , Weston Ralph E. 
Published: January 2005

A photometric method of determining hydrogen-atom concentration in the gas phase has been developed. It consists of a hydrogen—neon lamp emitting Lyman-α radiation at 1216 Å, and a nitric oxide-filled ion chamber which serves as the detector. A fast-flow system with a microwave discharge in an H2–He mixture was used as the source of hydrogen atoms. This arrangement permits the determination of H-atom concentrations of 1011 atoms/cc. A photometric calibration curve was obtained by using titration with NO2 as an absolute measure of H-atom concentration.
The oscillator strength of the Lyman-α transition was determined with this apparatus. Depending on the assumed profile of the emission line and the extent of self-reversal in the source, oscillator strengths of 0.4 to 1.1 (compared with the theoretical value of 0.8324) were obtained.
Rates of reaction of H atoms with ethylene and acetylene were determined at various total pressures and concentrations of reactants. Both reactions are first order with respect to each reactant, and the recombination of H atoms contributes very little to their rate of disappearance. The pressure effect on the reaction with ethylene depends on the formation of vibrationally excited ethyl radicals which either decompose to form reactants or are stabilized by collision. The reaction with acetylene appears to be complicated by a pressure-independent reaction path which predominates at low pressures and is most probably the abstraction reaction H+C2H2→H2+C2H.
Vibrational Relaxation Times of Deuterium and Hydrogen. A Comparison of Theory and Experiment
Authors: Parker J. G. 
Published: January 2005

A comparison of experimental and theoretical vibrational collision numbers has been carried out for deuterium and hydrogen and also for interactions of those gases with argon and krypton. Agreement is obtained for the latter while definite discrepancies appear for the D2—D2 and H2–H2 interactions. This discrepancy is rather large at the lowest temperatures; however, extrapolation of the experimental data indicates that at temperatures of the order of 10 000°K agreement is attained.
The intermolecular interaction constants used in comparing theory and experiment are shown to be consistent with those derived from measurements on rotational relaxation times for hydrogen and hydrogen—rare-gas mixtures. Using these interaction constants a value of 67 collisions is obtained for the rotational collision number of hydrogen in the limit of very high temperature.