bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interdependence of Spectral Line Breadth, Sound Velocity Dispersion, and Viscosity of Small Molecules in the Gas Phase
Authors: Bird George R. 
Published: January 2005

An examination of the data on bimolecular collisions of small molecules has produced several new insights and predictions. The data on viscosity, sound velocity dispersion, and spectral line breadths in the microwave, infrared, and Raman regions have been assembled for H2, O2, N2, CH3Cl, and HCN. These data have been put on an equivalent basis of calculated or observed spectral line breadth constants. When this is done, the relative importance of elastic and inelastic rotational collisions may be assessed.
The data on H2 are here used to predict a collisional narrowing of the ordinary Doppler linewidth; this narrowing effect can be found in the literature, where the significance of the extremely narrow lines has not been fully appreciated.
The line breadths observed in the microwave spectrum of oxygen are seen to be peculiar to some phenomenon which reorients electron spins but does not alter rotational states. Spin exchange is here identified as the most probably mechanism for microwave line broadening in O2.
The differences between isotropic and anisotropic linewidths in the Raman spectra of H2, O2, and N2 indicate that a thorough theoretical treatment of Raman linewidths is required. Some additional experiments on line breadths in the Raman spectra of H2, O2, and N2 are suggested. The basic approximation in Anderson's impact theory for broadening of spectral absorption and emission lines is seen to be quantitatively invalid for self-broadening of these homonuclear diatomic molecules. This is the approximation of classical (straight) paths.
Two new phenomena are predicted for the propagation of rotational energy in small polar molecules. The first of these is a separation of the rotational sound velocity dispersion into two regions for symmetrictop molecules. The region of lower frequency dispersion should account for R/2 of heat capacity, and be associated with changes in rotation about the unique axis of the molecule. Small polar molecules with large dipoles (particularly the alkali halide vapors) should also exhibit a peculiar form of energy propagation in the rotational degrees of freedom only. This ``roton propagation'' may also influence the behavior of shock waves in polar gases and the heat conductivity at very low pressures.
Microwave Spectra and Structure of Dimethyl Ether
Authors: Blukis Uldis , Kasai Paul H. , Myers Rollie J. 
Published: January 2005

The microwave spectra of six isotopic species of dimethyl ether were investigated from 8–48 Gc. From the changes in moments of inertia with C13 and O18 substitutions the CO distance and &lt;COC were found to be 1.410±0.003 Å and 111°43′±20′, respectively.
The conformation of the methyl groups was determined from the (CH2D) (CH3)O species. Dimethyl ether has C2v symmetry and the methyl groups are staggered with respect to the opposite CO bonds.
The data from deuterium substitutions could only be satisfactorily fit by a structure containing asymmetric methyl groups. The two CH distances in this structure differ by 0.009 Å, the &lt; HCH by 49′, and the angle between the CO internuclear line and a perpendicular to its respective hydrogen plane is 2°31′±40′. If an average CH distance of 1.0956 Å is assumed the average &lt;HCH is 109°29′. The structure of the asymmetric methyl groups is shown to be consistent with s and p hybridization of the carbon orbitals. In this scheme the carbons form ``bent bonds'' with the oxygen.
From the Stark effect the dipole moment of dimethyl ether was determined to be 1.31±0.01×10—18 esu.
Spin—Orbit Coupling and the Radiationless Processes in Nitrogen Heterocyclics
Authors: El-Sayed M. A. 
Published: January 2005

The matrix elements of the spin—orbit operator between the zero-order (spin-free) (n, π*) states of nitrogen heterocyclics are examined. It is found that generally, to the first order, there is no spin—orbit coupling between singlet and triplet states of the same configuration. The coupling between states of different configurations due to differences in the occupancy of the π* orbitals, but having the same nonbonding orbital, is found to have matrix elements similar to those resulting from the coupling between (π, π*) states, which McClure has shown to be unimportant. For the diazines (or polyazines), the coupling between different configurations due to a different occupancy of the nonbonding orbitals is found to have matrix elements which cancel one another. The general conclusion is thus reached that spin—orbit (s.o.) coupling between singlet and triplet (n, π*) states is unimportant to the first order. Using the observed polarization and lifetime data, it is estimated that the ratio |〈S(n,π*)|Hs.o.|T(n,π*)〉〈S(π,π*)|Hs.o.|T(n,π*)〉|2has an upper value of 10—3. These results as well as vibrational overlap considerations suggest that the enhancement of the efficiency of the intersystem crossing in nitrogen heterocyclics with the lowest singlet state of the (n, π*) type might be due to an S(n, π*)→T(π, π*) rather than an S(n, π*)→T(n, π*) radiationless process. An alternative explanation to the one previously given for the observation of fluorescence of 9, 10-diazaphenanthrene and s-tetrazine is thus suggested. In these molecules, the strong interaction between the (n, π*) singlet levels might cause the lowest S(n, π*) excited level to have a lower energy value than the (π, π*) triplet level. This would therefore lead to a retardation of the intersystem crossing process and allow the fluorescence to be observed. The characteristics of the observed weak phosphorescence of 9,10-diazaphenanthrene give spectroscopic support for this proposal.
For nitrogen heterocyclic molecules with the lowest singlet and lowest triplet states of the (π, π*) types, an examination of the quinoline total emission in comparison with that of the parent hydrocarbon, nath-thalene, suggests an increase in the efficiency of the intersystem crossing process in quinoline. This is suggested to be due to the efficient S1(π, π*)→T2(n, π*)→T1(π, π*) radiationless process. A probable enhancement of the internal conversion processes in these molecules is suggested to be due to an increase in the density of states and the efficiency of the S(π, π*)↔S(n, π*) radiationless process due to a large vibrational overlap integral.
Self-Diffusion and Impurity-Controlled Proton Relaxation in Liquid Methane
Authors: Gaven J. V. , Waugh J. S. , Stockmayer W. H. 
Published: January 2005

Self-diffusion in liquid methane, under its own vapor pressure, has been studied between the triple point and the normal boiling point by means of the spin-echo technique. The activation energy for self-diffusion is approximately 0.67 kcal/mole. These results are compared with the constant-pressure tracer results of Naghizadeh and Rice [J. Chem. Phys. 36, 2710 (1962)], which show somewhat higher (∼15%) self-diffusion coefficients and an activation energy of approximately 0.83 kcal/mole. The temperature dependence of self-diffusion in liquid methane appears to be comparable on the basis of a classical reduction to corresponding states, by means of critical constants, to that in liquid Ar, Kr, and Xe.
Measurements of the proton spin-lattice relaxation time in our sample indicate that the relaxation is predominantly controlled by the mutual diffusion of the hydrocarbon and small amounts of dissolved oxygen.
Electron Transfer Among the Transition Elements; the Controlling Role of the Franck—Condon Principle on Rates
Authors: Libby W. F. 
Published: January 2005

The principle [W. F. Libby, J. Phys. Chem. 56, 863 (1952)] that electrons cannot be readily exchanged between aqueous ions of different valence, unless they possess sufficient geometrical similarity to reduce to a minimum the energy transfer required by the simultaneous and instantaneous conversion of an ion of one valence to another while a second is changed in the exact opposite way, has now been firmly established. The Franck—Condon principle as applied to electron movement as well as to optical transitions thus has been found to be completely commanding in the case of electron exchange reactions between transition element ions in aqueous solution; e.g., Fe2+ and Fe3+ exchange electrons slowly while Fe(CN)64+ and Fe(CN)63— exchange very rapidly. Rapid electron exchange occurs also between MnO4—— and MnO4— even though the oxygen atoms do not exchange. Thus a type of tunneling of electrons is firmly proved to occur when the source and sink (reducing and oxidizing) ions (or molecules) satisfy the requirement of the Franck—Condon principle of being sufficiently similar geometrically to leave little need for change in hydration energy after the electron transfer.
It seems clear that this principle should apply also to oxidation and reduction reactions among the transition elements, and the present work examines the available kinetic data (particularly those of Taube and co-workers) to establish the extent of this applicability which appears to be substantial.
Kinetics of Reactant Isolation. I. One-Dimensional Problems
Authors: Cohen E. Richard , Reiss H. 
Published: January 2005

This paper treats the time-dependent statistics of bond formation (both irreversible and reversible) between fixed sites. This model corresponds to a number of real physical processes. Among these are reaction of adjacent functional groups on a linear polymer, matrix isolation of free radicals, and chemisorption. Because the sites are fixed, certain of them become isolated from others, not yet reacted, and must survive to infinite time. A certain amount of survival occurs even when bonds can be undone.
Exact descriptions of the kinetics of these processes are given for one-dimensional systems. The mean probability of site survival as a function of time is calculated for linear arrays and for rings. The probability of site survival as a function of position on the chain (end effects) is treated in Sec. IV. A generating function is introduced in order to calculate higher moments of the survival probability distribution function and to treat the effect of a random diluent. An approximate method of solution is developed for the time dependence of the number of reacted particles in the reversible case.
Primary Reactions in the Mercury Photosensitized Decomposition of Butene-2 at Low Pressures
Authors: Kebarle P. , Avrahami M. 
Published: January 2005

The reaction was studied in a flow system attached to a mass spectrometer. The pressure of the butene was in the micron range while He at a pressure of 10 mm was used as a carrier gas. Under these conditions it was found that the greater part of the excited butene-2 is deactivated.
The decomposition proceeds by two primary reactions: 2−C4H8*→CH3CHCHCH2+H,2−C4H8*→ lim rearrangementallyl+methyl.The two reactions occur roughly in the ratio 2.5:1. A rearrangement to methylcyclopropane occurs to a very minor extent if at all.
Photoconductivity in Metal-Free Phthalocyanine Single Crystals
Authors: Heilmeier George H. , Warfield George 
Published: January 2005

The spectral response of photoconductivity in metal-free phthalocyanine crystals was obtained in the region 2500–25 000 Å, and was found to have the same response edges as the optical absorption spectrum. The correspondence between the valley-to-valley separation of the structure found in the strong response regions of the spectral response of photoconductivity and the peak-to-peak separation of the infrared optical absorption spectrum has been used to formulate a model for photoconductivity in metal-free phthalocyanine crystals which involves the direct creation of carriers by suitable radiation.
An expression for the effective lifetime of a photoexcited carrier in a crystal with a finite surface recombination velocity was derived. This was found experimentally to be approximately 0.9×10—8 sec. Using this lifetime and the mobility determined by Hall-effect measurements, the diffusion length for electrons was calculated to be 5×10—6 cm. A comparison of this diffusion length with the reciprocal of the extinction coefficient indicates that the free carriers excited by 7300-Å radiation are produced further from the surface than a diffusion length. Thus, the lifetime of the free carriers should be more nearly characteristic of the bulk. The experimentally determined lifetime is in rough agreement with the theoretical decay time for fluorescence. This emphasizes the importance of the first excited singlet state in the conduction process. The structure of the spectral response of photoconductivity was used in conjunction with previous discussions of the applicability of the band model to infer the nature of the conduction band in metal-free phthalocyanine crystals.
Analysis of the Spectra of Tripositive Praseodymium in Ethylsulfate Crystals
Authors: Gruber John B. 
Published: January 2005

In the first portion of this paper a theoretical calculation is presented for the ``free-ion'' spectrum of Pr3+ (4f2). A least-squares calculation is made to obtain a set of Slater and spin-orbit parameters that gives a theoretical spectrum in closest possible agreement with the observed absorption spectrum of Pr3+ (4f2) in ethylsulfate crystals. The disagreement between the calculated and observed spectrum may be explained as due primarily to the neglect of the configuration interaction in the ``free-ion'' calculation, and to a much smaller extent as due to the effect of the lattice environment surrounding the Pr3+ (4f2) ion.
In comparing the spectrum of Pr3+ (4f2) in ethylsulfate crystals with the spectrum of the same ion in other crystals, the shift in energy of the J levels may be explained as due to the difference in chemical bonding in the various crystals. This ``chemical bonding'' shift may be accounted for by a simple change in the Slater and spin-orbit parameters.
Assuming that the local symmetry about the Pr3+ (4f2) ion is D3h, a first-order perturbation calculation is carried out for the crystal-field split components of the Pr3+ (4f2) ion J-levels, 3P2, 1I6, 3P1, 3P0, 1D2, 1G4, 3F4, 3F3, and 3H4.
The following set of lattice parameters, Anm 〈rn〉, obtained by a least-squares calculation, gives the best over-all agreement between the theoretical and observed spectrum: A20 〈r2〉=16.32 cm—1, A40 〈r4〉=—83.46 cm—1, A60 〈r6〉=—45.76 cm—1, and A66 〈r6〉=530.21 cm—1. A more complete calculation is then made using an IBM 7090 program that diagonalizes the entire intermediate-coupling and D3h crystal-field-splitting matrix. Again, from a least-squares calculation, the following ``best'' set of parameters is found: F2=307.4 cm—1, F4=49.44 cm—1, F6=5.138 cm—1, ξ=727.9 cm—1, A20 〈r2〉=15.31 cm—1, A40 〈r4〉=—88.32 cm—1, A60 〈r6〉=—48.76 cm—1, and A66 〈r6〉=548.48 cm—1. When one compares the theoretical energy spectrum based on these parameters with the observed spectrum, one finds an average deviation of 3.0 cm—1, and a standard deviation of only 1.0 cm—1.
Energy Evolution in Pd2H below 1°K
Authors: Fritz J. J. , Maria H. J. , Aston J. G. 
Published: January 2005

Energy evolution below 1°K has been observed in β-phase palladium hydride (formal composition Pd2H). The rate of evolution was strongly temperature-dependent below 0.1°K, but became temperature-independent between 0.1° and 1.0°K. It depended upon previous specimen history and was greatly reduced by annealing of the specimen below 50°K. For specimens kept below 1°K, the rate of energy production at a given temperature diminished with a half-life of about 8 h.
The results are explained semiquantitatively as a (spectroscopically forbidden) nuclear-spin conversion in quasi-molecular PdH4 units left behind in small concentrations when the lattice is cooled through the rotational transition (at 55°K) of β-palladium hydride. The temperature-dependence below 0.1°K appears to result from limitation in the rate at which the lattice can remove the change in librational energy associated with the conversion process.
Hydrogen—Helium Ion—Molecule Reactions
Authors: von Koch Helge , Friedman Lewis 
Published: January 2005

The reactions producing HeH+ from gaseous mixtures of H2 and He subjected to electron impact in the ion source of a mass spectrometer have been studied. Ionization efficiency curves show practically all of the HeH+ to be formed by reaction of H2+ and He. Phenomenological cross sections were compared with values for the formation of H3+ from the H2+–H2 present in the ion source. The maximum value of the ratio of rate constants for HeH+ and H2+ formation computed from the experimental data was 28% of the theoretical ratio. If the heat of the endothermic reaction between H2+ and He is supplied from internal energy in H2+, then the rate constant should be computed in terms of the fraction vibrationally excited H2+ with sufficient internal energy to meet the needs of the reaction rather than total H2+ in the ion source. An estimate of the population of the excited vibrational state in H2+ produced from H2 by electron impact gives approximately 29% with enough energy to react. The translational energy dependence of the ratio of rate constants reveals a kinetic energy threshold for the HeH+ reaction of about 0.35 eV, but at higher ion kinetic energy there is strong evidence for heat of reaction coming primarily from internal energy in H2+.
An attempt was made to use the HeH+ reaction as a probe to investigate the distribution of excited H2+ produced from CH4 by electron impact. A third-order process giving HeH+ was discovered in this system. Indications of a larger yield of H2+ with sufficient energy to react with He were obtained.
Influence of Vibration—Rotation Interaction on the True Vibrational Wavefunctions
Authors: Jain D. C. 
Published: January 2005

A method is suggested for obtaining the true vibrational wavefunctions corrected for vibration—rotation interaction by the application of perturbation theory. For this purpose the harmonic oscillator wave-functions have been considered to be perturbed by the potential V′=[U(r)−V0(r)]+[ℏ2J(J+1)/2μr2],where U(r) is the true potential, V0(r) is the harmonic oscillator potential and [ℏ2J (J+1) /2μr2], the vibration—rotation interaction term.
Expressions are given for the integrals ∫ ψ̄v′J′ψv′′J′′dr  and   ∫ ψ̄v′J′ξψv′′J′′dr,which occur in the transition-moment matrix elements for electronic bands. Similar integrals occurring in the dipole-moment matrix elements for vibration—rotation bands, can also be evaluated by using these wavefunctions.
Interactions in Polar Media. I. Interparticle Interaction Energy
Authors: Marcus R. A. 
Published: January 2005

Using permanent plus induced charge distributions on particles a Hartree method is used to compute the polar contribution to the interparticle interaction enerby. Each particle may be a single molecule or a coll?ction of molecules, a whole electrode or an entire medium for example. The total interparticle interaction energy is taken to be the sum of this polar term and of an interparticle electron correlation term. The second of these includes effects due to interparticle London dispersion and exchange repulsion forces. A symmetry property associated with a quantum mechanical operator characterizing the induced charge distribution is obtained in a compact way using a projection operator. The polar term is also calculated from classical electrostatics and shown to be the same as the one above. The present work is a generalization of earlier treatments in which the particles were single molecules interacting via permanent and induced dipoles.
An application of this work is the more general formulation of theories associated with polar interactions in condensed phases, such as the theory of electron transfer rates in solution and at electrodes, and the theory of electronic spectral shifts and band broadening of polar solutes in polar media.
Extended Basis-Set LCSTO—MO—SCF Calculations on the Ground State of Carbon Dioxide
Authors: McLean A. D. 
Published: January 2005

Extended basis-set SCF—STO—MO wavefunctions for the ground state of CO2 are reported. In particular, the effect of doubling the number of 2pσ basis functions and the effect of changing their orbital exponents has been investigated, together with the effect of addition of 3dσC basis functions. The effect of expanding the π basis set by addition of extra 2pπC basis functions and 3dπO1, O2 basis functions is also shown. A wave-function using the best σ basis set together with the best π basis set used in these calculations would give a molecular energy of approximately 9 eV below that obtained from a `best atom' minimal basis-set calculation. This is to be compared with the estimated Hartree—Fock molecular energy which is approximately 24 eV below the ``best atom'' minimal basis-set value. This highlights the importance of the choice of basis functions and minimization of the total energy with respect to orbital exponents in the case that the number of basis functions out of which MO's can be constructed is limited.
The quadrupole moment of CO2 is computed from two of the wavefunctions reported.
Gaseous Diffusion in Porous Media. III. Thermal Transpiration
Authors: Mason E. A. , Evans R. B. , Watson G. M. 
Published: January 2005

A previously proposed model for the diffusion of gases in porous media at uniform and nonuniform pressures has been extended to allow for temperature gradients. The porous medium is visualized as a collection of ``dust'' particles constrained to remain stationary in space. As before, by formally treating the ``dust'' particles as giant molecules, it is possible to cover the entire range of intermediate mechanisms from the Knudsen to the normal region by varying the mole fraction of the real gas. For binary systems (a single gas and ``dust''), the phenomenon of thermal transpiration is accounted for by the model in a consistent way for all aspects which are diffusive in character but, as before, needs modification at high pressures by the addition of an expression to account for the viscous backflow. With this modification, an equation is obtained which describes thermal transpiration over the entire pressure range. This equation discloses two new relationships not previously noticed: one between the maximum in the thermal transpiration curve and the Knudsen minimum in the permeability curve, and one between the height of the thermal transpiration maximum and the translational heat conductivity of the gas.
It was found that it was possible to extend the model to include capillaries as well as porous media. This extension disclosed that the relationships applicable to porous media would also describe the analogous behavior that occurs in capillaries with definite geometry. The capillary results reproduce previous semi-empirical and empirical equations of Weber and Liang for thermal transpiration, and the permeability equation of Knudsen. The present equations, however, have fewer adjustable parameters than do the previous equations. A simple connection, not previously mentioned, between Weber's and Liang's equations was also noticed: Liang's equation is really a special form of Weber's equation written in a differential-approximation form.
A remarkable feature of the results, as applied to capillary systems, is that one can calculate rotational relaxation times in gases from the height of the thermal transpiration maxima, which suggests much simpler experimental techniques than those previously employed for the measurement of this phenomenon.