bluuebunny/crossref_metadata_2025_split huggingface dataset:
Forbidden Band Systems in Nitrogen. II. The a′1Σu−←X1Σg+ System in Absorption
Authors: Wilkinson P. G. , Mulliken R. S. 
Published: January 2005

Four bands of the a′1Σu−←X1Σg+ system in nitrogen have been observed in absorption at high resolution in a path of 3.4 meteratmospheres, at 1444 A (1–0), 1414 A (2–0), 1358 A (4–0), and 1331 A (5–0). They consist of Q branches only (ΔJ=0). The observation of these bands, highly forbidden by the usual selection rules, is explainable by perturbations with the nearest 1IIu states lying between about 98 000 cm—1 and 109 000 cm—1 above the ground state.
The rotational analysis of each of the bands resulted in rotational constants and vibrational intervals for a′1Σu— which agree very well with those obtained from the emission system x1Σg−→a′1Σu−. The electronic energy (T00) of state a′1Σu— is now precisely located at 67738.18 cm—1 (8.398 ev); this value combined with other data gives also the following electronic energies (T00): w1Δu, 71697.68 cm—1 (8.889 ev); x1Σg—, 113210.98 cm—1 (14.036 ev); and y1IIg, 114165.18 cm—1 (14.154 ev). T00 of a′1Σu— is close to that of a 1IIg: 68951.21 cm—1 (8.548 ev).
The new energy for y1IIg is 0.339 ev lower than the minimum value deemed possible by Lofthus and Mulliken on the basis of an observed predissociation at v=0, J=10 of state y. That predissociation is now reinterpreted as most probably an accidental one resulting in the formation of 2P+4S atoms instead of 2D+2D atoms as formerly assumed.
The intensity distribution in the a′1Σu−←X1Σg+ system is found to be approximately proportional to J(J+1)(2J+1) exp—[B0″J(J+1)hc/kT], where B0″=1.9898 cm—1 and T=300°K, in agreement with theory.
From appearance pressures of the five forbidden systems of nitrogen now known in absorption, it is possible to estimate the transition probabilities. From these, together with a recent molecular beam determination of the mean lifetime of the state a1IIg, it is possible to estimate the lifetimes of the metastable states: A3Σu+, 2.6×10—2 sec, a′1Σu—, 4.0×10—2 sec. By comparison of the transition probability of the atmospheric oxygen bands (b1Σg+←X3Σu−) with that of the Vegard-Kaplan bands of nitrogen (A3Σu+←X1Σg+), together with the known lifetime of b1Σg+, the value 6.5×10—3 sec is found for the lifetime of A3Σu+, in fair agreement with the value given above.
C13 Splittings in Proton Magnetic Resonance Spectra. I. Hydrocarbons
Authors: Muller Norbert , Pritchard Donald E. 
Published: January 2005

Indirect spin-spin couplings between protons and C13 nuclei have been measured for a number of hydrocarbons. The results are interpreted on the basis of a simple semiempirical equation relating the coupling constants with the amounts of s character of the carbon-atomic orbitals involved in the bonds. No evidence is found for a dependence of the coupling constants on supposed changes in ionic character of the bonds.
An equation is also presented relating the coupling constants and the C–H internuclear distances. This provides a new indirect means of evaluating C–H distances, with a reliability apparently at least comparable with that of methods in current use.
Further Studies of the Pyrolysis of Dimethyl Ether
Authors: Benson Sidney W. , Jain D. V. S. 
Published: January 2005

The pyrolysis of dimethyl ether has been investigated over the pressure range 35 to 400 mm Hg and the temperature range 750 to 820°K in a quartz flask. The results confirm the previous designation of an initial 32-order rate relative to Me2O but yield an activation energy of 55.6 kcal. This can be explained if it is assumed that CH3OCH2 is an important chain breaker and that the reaction CH3OCH2→CH3+CH2O is an energy transfer process in its second-order region. The small catalysis provided by added N2 and CH4 is supporting evidence for this. Further evidence comes from the observed rate of exchange of deuterium gas with Me2O which is now in good accord with calculation.
Values of the rate constants for CH3 radical attack on H2 and D2 are in good agreement with those extra-polated from much lower temperatures. Some new values of rate constants are reported as well as new estimates of frequency factors and activation energies for various chain steps. There is some evidence for heterogeneous disappearance of H atoms at the wall, including a temporary inhibition observed in KCl-coated vessels. Small amounts of added O2 have little effect on the rate while C2H4 is a very powerful inhibitor. At 780°K, chain lengths vary from 21 at 25 mm Hg to 84 at 400-mm Hg pressure. They decrease slowly with increasing temperature.
3ν3 Band of C12S32S34
Authors: Guenther Arthur H. 
Published: January 2005

The 3ν3 band of C12S32S34 at 4556.553 cm—1 has been investigated. The following molecular constants, expressed in cm—1, were obtained: B′+B′′=0.209702,α3=0.000691,B′−B′′=−0.002073,ν0=4556.553,D′=D′′=4B3/ω12=1.12×10−8,r0=1.5544×10−8cm.
It is believed that this is the first resolution and analysis of the rotational structure of C12S32S34 in the infrared region. When the results of this investigation are compared to those of ordinary carbon disulfide, C12S232, they are found to be consistent with the relations governing the effect of isotopic substitution on the molecular constants. The value for the internuclear distance, r0 = 1.5544 A, obtained in this investigation is in good agreement with the value obtained for ordinary CS2, i.e., r0 = 1.5545 A.
Abnormal Excitation of OH in H2/O2/N2 Flames
Authors: Kaskan Walter E. 
Published: January 2005

The emission from the first four vibrational levels of OH2Σ+ and the concentrations of ground state OH2II have been measured in a series of rich H2/O2/N2 flames held on flat porous burners as a function of distance from the burner. The intensity of emission of each of the bands is proportional to the cube of the concentration of ground state OH, but the constant of proportionality depends on the band and the flame conditions. This dependence, as well as absolute intensity measurements, establish the fact that the radiation is nonthermal.
The dependence of the emission intensity on an integral power of OH strongly indicates that the excited OH is formed as a result of one or more of a set of possible radical recombination reactions. It is shown that in general it is not possible to obtain a unique determination of the excitation mechanism for any band. The only exception to this is that definite evidence for the preassociation reaction, O+H→OH2Σ, v=2, has been obtained. The vibrational distributions of excited OH are shown to be consistent with ``temperatures'' from 3000°K to 5000°K (compared with maximum flame gas temperatures of 1600°K), which is probably to be expected from a reaction with the exothermicity of H+OH+OH→H2+OH*. It is concluded from this and from the general behavior of the data, that this last reaction is most likely responsible for the nonthermal emission of all the bands, with the exception of that specifically known to be due to the preassociation reaction.
Molecular Transport in Liquids and Glasses
Authors: Cohen Morrel H. , Turnbull David 
Published: January 2005

We have derived, by using simple considerations, a relation between the diffusion constant D in a liquid of hard spheres and the ``free volume'' vf. This derivation is based on the concept that statistical redistribution of the free volume occasionally opens up voids large enough for diffusive displacement. The relation is D=A exp[−γv*/vf], where v* is the minimum required volume of the void and A and γ are constants. This equation is of the same form as Doolittle's [J. Appl. Phys. 22, 1471 (1951)] empirical relation between the fluidity φ of simple hydrocarbons and their free volume. It has been shown [Williams, Landel, and Ferry, J. Am. Chem. Soc. 77, 3701 (1955)] that the Doolittle equation also can be adapted to describe the abrupt decrease in molecular kinetic constants with decreasing temperature that accompanies the glass transition in certain liquids. Our result predicts that even the simplest liquids would go through this glass transition if sufficiently undercooled and crystallization did not occur. The problem of transport in actual simple and network liquids also is discussed.
It is shown that data on self-diffusion in some simple van der Waals liquids and liquid metals are described satisfactorily by our relation with v* near the molecular volume for the van der Waals liquids and near the volume of the ion, corresponding to the highest valence state, for the metals.
Line Shape and f Value in the OH 2Σ+ — 2Π Transition
Authors: Carrington Tucker 
Published: January 2005

Line shape and f value in the ultraviolet transition 2Σ+—2Π of OH have been studied by the curve of growth method, and rough direct measurements of line width have been made. The lines Q16, P16, R16, Q216, and S16 fit a curve of growth indicating a collision broadening width of 0.02±0.02 cm-1 at 2600°K and 1 atmos in flame gases of the approximate composition O2 60%, H2O 20%, and CO2 20%. For the Q16 line, the f value is (11.7±4)×10-4. This corresponds to a radiative lifetime for the free molecule of 5.5×10-7 sec, in excellent agreement with the earlier work of Oldenberg.
Brief discussions are given of theoretical limitations on the use of the curve of growth, and of the qualitative factors to be considered in explaining the observed line width.
Determination of Absorption Coefficients from Infrared Dispersion Data
Authors: Kagarise R. E. 
Published: January 2005

Liquid dispersion data in the neighborhood of the 14μ absorption bands of CCl4 and the 9μ band of CH2I2 have been analyzed in terms of the Kramer dispersion equation. The so-called oscillator strengths obtained from the dispersion data were found to be in good agreement with those obtained directly from integrated absorption coefficients.
The liquid state absorption coefficients for the 9μ band of CH2I2 are essentially equal to that previously reported for the vapor state. Thus it would appear that the Polo-Wilson ratio of intensities is not satisfied in this case.
Participation of Vibration in Exchange Reactions
Authors: Smith Felix T. 
Published: January 2005

Exothermic exchange reactions of the type A+BC→AB+C sometimes leave the product AB in a highly excited vibrational state. Simple theoretical considerations related to the description of the molecular collision show that the fraction of the reaction energy available for this vibrational mode is limited by the kinematic factor sin2β, where β is the angle of rotation required to take a coordinate system describing the reactants into one suited to the products, and tan2β=(mB/mA)+(mB/mC)+(mB2/mAmC). In the reaction A+BCD→AB+CD, similar results apply to the newly formed bond AB, and no excitation of vibration in CD is predicted. Although effects to be expected from details of the potential energy surface are ignored, comparison of the kinematic factor alone with experimental results shows excellent agreement.
Applied to the reverse reaction, the theory gives a criterion for predicting the effect on the reaction rate of the distribution of energy between translational and vibrational modes in the collision. In the reaction O3+O2*→O+2O2, it is predicted that the oxygen atom comes preferentially from the vibrationally excited oxygen molecule.
Incidentally, it is shown that the transformation from a properly normalized center-of-mass coordinate system describing the reactants to one describing the products can always be resolved into a sequence of simple rotations.
Mean-First-Passage Times and the Collision Theory of Bimolecular Reactions
Authors: Widom B. 
Published: January 2005

A general collision theory is outlined for the kinetics of reaction of molecules which are dilutely dispersed in an inert gas, reaction being the result of binary collisions between the reacting molecules and the inert gas molecules. It is assumed that the products of reaction are instantaneously removed from the system. The mean-first-passage time for the transition from reactant to product states is expressed in the classical theory in terms of the solution of an integral equation in which the kernel is the transition probability per unit time between two states of the reacting molecule. As shown by Kim, when a rate constant exists (which is not always the case) it is the reciprocal of the mean-first-passage time. In a one-dimensional system, or in a system of two or three dimensions where the interaction between colliding molecules has a finite range, there exists a finite collision number Z which is independent of the internal state of the reacting molecule. In such a case there is a Liouville-Neumann solution of the integral equation which allows the mean-first-passage time to be expressed as a sum of contributions corresponding to failure to react after no collisions, after one collision, after two collisions, etc.
The equilibrium hypothesis is analyzed and it is seen what the precise nature of that approximation is.
The theory is illustrated with each of two transition kernels, both satisfying the conditions of completeness and detailed balance. The first is a very simple but physically unrealistic one in which the transition probability depends only on the final state but not on the initial state, and here it is found that the equilibrium hypothesis yields the exact rate constant without error. The second illustration uses the previously calculated transition probability for a one-dimensional string oscillator suffering impulsive collisions with particles of mass identical to its own, and counts the oscillator as ``dissociated'' when its energy exceeds a certain critical energy ε*. Here, as is obvious, the equilibrium hypothesis is correct when ε*≫kT, and it is found that in this range the rate constant for dissociation is Z(kT/πε*)12exp(−ε*/kT). It is shown in an Appendix that if instead of just formally calling the oscillator dissociated when its energy exceeds ε*, one actually specifies that the string is then ruptured, the basic transition probability is altered, and the equilibrium hypothesis then yields for the dissociation process the even simpler rate constant Z exp(—ε*/kT).
Proton Magnetic Resonance Study of Lithium Sulfate Monohydrate
Authors: McGrath J. W. , Silvidi A. A. , Carroll J. C. 
Published: January 2005

An extended proton magnetic resonance study of lithium sulfate monohydrate is presented. An oddity in the resulting Pake curves appears. Some of the curves show a shift so that they are described by equations of the form, ΔH=2α[3 cos2(φ+φ0) cos2δ−1] +constant shift.
There are two orientations of the hydrated water molecule. For these the direction angles of the proton-proton axes with respect to the crystallographic a, b, and c axes are, respectively, α0=97°, β0=45°, γ0=48°, and α0=74°, β0=38°, γ0=127°. Apparently the hydrogens bond O5— —H–O5–H— —O1, where O5 are neighboring water oxygens and O1 is a sulfate oxygen.
Several possible origins of the shifts in the Pake curves are discussed with limited success. An adequate theoretical explanation is lacking.
Nonequilibrium Kinetics and Chromatography
Authors: Giddings J. Calvin 
Published: January 2005

An effort is made here to deal with the complex kinetic processes which determine the structure of component zones in chromatography. The problem is approached by assuming that the various steps are proceding near equilibrium. In order to facilitate the analysis an approximation is made in which each derivative of a concentration is replaced by the derivative of the equilibrium concentration. The latter derivatives are evaluated in terms of the concentration profile. This yields a set of linear algebraic equations from which an equilibrium departure term, ε, can be found for each species. The diffusion of the zone is then obtained as a function of the various ε's.
The simplicity introduced by this method allows one to obtain the zone diffusion term for complex kinetics in contrast to the rigorous theories where only the simplest kinetic schemes have been treated. The results for a simple kinetic example are the same, however, as obtained in the limit of large times by the rigorous methods. The validity of the assumptions made is established independently of this comparison. Various applications of the method are discussed which extend beyond the range of chromatographic analysis.
Contribution of Bound, Metastable, and Free Molecules to the Second Virial Coefficient and Some Properties of Double Molecules
Authors: Stogryn Daniel E. , Hirschfelder Joseph O. 
Published: January 2005

The second virial coefficient for molecules interacting with a spherically symmetric potential is divided into three parts: (1) a contribution Bb, related to the equilibrium constant for the formation of bound double molecules; (2) a contribution Bm, related to the equilibrium constant for the formation of metastably-bound double molecules; and (3) a contribution Bf, due to molecules which interact but are free to separate after the interaction. Equations are given for determining each of the three parts of the second virial coefficient. A detailed treatment of these three contributions together with numerical tables on a reduced temperature basis is given for the square-well, Sutherland, and Lennard-Jones (6–12) potentials.
The mean lifetimes of metastably bound double molecules are discussed, and numerical values are given for the special case of argon. Tables for computing mean lifetimes in other Lennard-Jones gases are given. It is found that most metastably bound double molecules have mean lifetimes considerably longer than the mean time between collisions at ordinary pressures. Finally, an equation is developed for the number of vibrational levels of a double molecule.
Initial Pressure Dependence of Thermal Conductivity and Viscosity
Authors: Stogryn Daniel E. , Hirschfelder Joseph O. 
Published: January 2005

The initial pressure dependence of thermal conductivity and viscosity of gases is considered to arise from molecular association and collisional transfer. Since only the initial pressure dependence is investigated, clusters larger than dimers can be neglected. The effect of dimer formation can be calculated from a knowledge of the equilibrium constant for the reaction 2A⇌A2. The effect of collisional transfer is obtained by a semiempirical modification of Enskog's theory. In the case of thermal conductivity, it is found that at low temperatures molecular association is more important than collisional transfer, while at high temperatures collisional transfer predominates. For viscosity, the initial pressure dependence is due primarily to collisional transfer.
Detailed equations for the initial pressure dependence of both thermal conductivity and viscosity are given in terms of dimensionless groupings which include the intermolecular potential parameters. Tables of these dimensionless groupings as functions of a reduced temperature are given for molecules obeying the Lennard-Jones (6–12) potential. Comparisons between theory and experiment are included. It is found that the numerical results are sensitive to the choice of force constants for the interaction of a monomer with a dimer.
Internal Rotation in Molecules with Two Internal Rotors: Microwave Spectrum of Acetone
Authors: Swalen J. D. , Costain C. C. 
Published: January 2005

The theory of internal rotation in molecules is extended to the case of two internal symmetric rotors attached to a molecule with C2v symmetry. The calculation of the internal rotational energy levels and of the interaction with the over-all rotational energy levels is discussed both for the high barrier and the low barrier approximation. The symmetry of the Hamiltonian for a molecule with the acetone structure is considered and the selection rules and relative intensities of the various fine structure components are derived.
The microwave spectra of acetone and of completely deuterated acetone have been measured and assigned. From the rotational constants, the molecular structure has been partially determined. The most probable values of the structural parameters are r0(C=O) = 1.215 A (assumed), r0(C–C) = 1.515±0.005 A, r0(C–H) = 1.086±0.010 A, ∠CCC = 116°14′±1°, and ∠HCC = 110°16′±1°. The angle between the axes of the methyl groups is approximately 3° larger than the ∠CCC.
The dipole moment has been determined to be 2.90 D by a measurement of the Stark effect on the microwave transitions.
Each of the rotational transitions is split into a number of components by the internal rotation. From an analysis of these patterns the barrier height to internal rotation is found to be 274 cm—1 for (CH3)2CO and 258 cm—1 for (CD3)2CO. The difference in the two calculated barrier heights and the errors in the method are discussed.
Total Collision Cross Sections for the Interaction of Atomic Beams of Alkali Metals with Gases
Authors: Rothe Erhard W. , Bernstein Richard B. 
Published: January 2005

Total collision cross sections (Q) for the interaction of atomic beams of K and Cs with a number of molecules were measured with an apparatus of 30″ angular resolution. Although absolute determinations of Q are difficult, relative values are readily obtained (±3%). Results are reported as the ratio (Q*) of the cross section for a given molecule to that of argon for the same beam atom. Seventy-seven molecules (of varied complexity and reactivity) were studied with K and 16 with Cs beams. Q* ranged from 0.29 to 2.8.
The data were correlated using the Massey-Mohr theory, assuming an attractive intermolecular potential V(r) = —C/r6. For this case Q=b(C/vr)2/5, where vr is the relative velocity and b a known constant. C was estimated from standard formulas for the London dispersion and dipole-induced dipole forces, using known refraction and dipole moment data. The theoretical values of Q differ by a nearly constant factor from the experimental results; thus values of Q* are predicted with good accuracy. The deviation between Qcalc* and Qobs* was &lt;±3% for 57% (and &lt;±10% for 87%) of the molecules. Most of the large deviations occurred for the light gases.
Infrared Spectrum of Crystalline Boron Trifluoride
Authors: Dows David A. 
Published: January 2005

Infrared spectra of various mixtures of isotopically substituted boron trifluorides are presented. The samples were studied in the solid state at 83°K, and in the spectral range covering all fundamental vibrations.
Multiplet structures and shapes of the absorption bands show that the crystal structure is not isomorphous with that of boron trichloride and tribromide, and that rather strong intermolecular coupling of vibrations prevails.
Normal Coordinates of the Planar Vibrations of Pyridine and Its Deuteroisomers with a Modified Urey—Bradley Force Field
Authors: Zerbi Giuseppe , Crawford Bryce , Overend John 
Published: January 2005

A Urey—Bradley potential function has been fitted to the observed vibrational frequencies of pyridine, pyridine-2,6-d2, pyridine-3,5-d2, pyridine-4-d1, and pyridine-d5.
As in the case of benzene, it was necessary to include an additional non-Urey—Bradley force constant ρ to describe the aromatic character of the molecule. Our results suggest several minor changes in the vibrational assignment of some of these molecules.