bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Singlet-Exciton States of Crystalline Anthracene
Authors: Silbey Robert , Jortner Joshua , Rice Stuart A. 
Published: January 2005

In this paper we present a detailed analysis of the lower excited states of crystalline anthracene. Starting with zero-order product wavefunctions, the treatment differs from standard formulations in that interactions between molecules are computed directly by the use of π-electron theory, by the inclusion of the effects of extensive configuration mixing, and by the inclusion of long-range interactions out to the convergence limit. It is found that:
(1) The computation of interaction energies cannot be reduced to dipole—dipole terms alone. By the use of π-electron theory it is shown that short-range high-order multipole (greater than dipole) interactions make important contributions to both the diagonal and off-diagonal elements of the energy matrix.
(2) Long-range interactions of the dipole—dipole type are of importance for distances of the order of the wavelength of light. By application of momentum-conservation conditions, it is shown that the long-range dipole—dipole interactions, including the effects of retardation of the potential, are absolutely convergent. Major contributions to the Davydov splitting arise from molecular separations ranging from 50 Å to the convergence limit.
(3) For the case of allowed singlet—singlet transitions, electron-exchange interactions are small relative to other contributions to the interaction energy.
(4) Under the experimental conditions used to date, the Davydov splitting should be independent of crystal thickness.
(5) In anthracene, crystal-field mixing of the p and β molecular states has a large effect on the Davydov splitting. Inclusion of mixing with higher excited π states has little effect on the Davydov splitting, but is required in the calculation of the polarization ratios in the vibronic components of the p band.
(6) Charge-transfer exciton states play only a minor role in altering the properties of singlet exciton states arising from allowed transitions.
(7) The detailed calculations reported herein yield good agreement with the observed Davydov splitting (ΔE) and polarization (P) ratios in anthracene, e.g., for the 1A1g→1B2u band: Vibronic bandΔE(calc.)(cm−1)ΔE(obs.)(cm−1)P(calc.)P(obs.)0–02072303.550–11021452.54.50–254801.93
Radio-Frequency and Microwave Spectra of 6Li127I by the Molecular-Beam Electric-Resonance Method
Authors: Breivogel F. W. , Hebert A. J. , Street K. 
Published: January 2005

The radio-frequency and microwave spectra of 6Li127I have been observed by the molecular-beam electric-resonance method of molecular spectroscopy. Spectra of 6Li127I in the first two vibrational states were obtained. From the J=1 radio frequency, Stark spectra values were obtained for the electric dipole moment μ, the iodine nuclear quadrupole interaction eqQI, and the iodine spin-rotation constant cI. The values of these constants are v=0v=1μ (debye)7.4285±0.0017.5120±0.001eqQI (Mc/sec)−198.780 ±0.005−207.453 ±0.010cI (kc/sec)7.7  ±0.47.8  ±0.6.
The observation of J=1→J=0 microwave transitions yielded the following rotational constants: B0=15 304.895±0.005 Mc/sec,B1=15 153.316±0.009 Mc/sec.
Molecular Magnetic Moments and Susceptibility in Formaldehyde
Authors: Flygare W. H. 
Published: January 2005

High-resolution microwave spectroscopy has been used to measure the molecular Zeeman effect in formaldehyde where both ΔM = 0 and ΔM = ±1 transitions were observed. The magnitudes and signs of the diagonal elements of the g tensor were determined.
The results for OCH2 are | gbb—gcc | = 0.08±0.03, gaa = −2.935±0.03, gbb = −0.17±0.05, and gcc = −0.11±0.05. These results combined with the value of the bulk susceptibility yield the following value depending on the ground-state wavefunction for OCH2: 〈ψ0 | Σiri2 |ψ0〉 = 14.61×10−16 cm2, where the sum is over all electrons.
The average value of the diamagnetic susceptibility in OCH2 is χd = −41.3×10−6. The average value of the paramagnetic susceptibility is χp = 40.8×10−6. The anisotropy in the paramagnetic susceptibility along the O–C bond is χ⊥p—χ∥p = 5.6×10−6 where χ⊥p is perpendicular to the CH2 plane.
Behavior of Thirteen Charge-Transfer Complexes at High Pressures
Authors: Bentley W. H. , Drickamer H. G. 
Published: January 2005

The effect of pressure to several hundred kilobars has been measured on the properties of 13 complexes containing aromatic molecules. These complexes are classified in four groups: those containing tetracyanoethylene (TCNE), those containing iodine, those involving p-phenylenediamine, and halogenated p-benzoquinones, and those involving the halogenated p-benzoquinones and other materials.
In all cases the resistance decreased rapidly with increasing pressure at low pressures. A number of complexes exhibited minima in resistance at pressures from 60 to 200 kbar and an irreversible rise at higher pressures. The nature of the irreversible process could in several cases be postulated from difference in the visible and infrared spectra between the transformed and untransformed complexes.
Elementary Rates of Decomposition of the Homologous Series Ethyl through 2-Octyl Radicals
Authors: Pearson M. J. , Rabinovitch B. S. 
Published: January 2005

The rates of decomposition of the secondary alkyl radicals 2-butyl, 2-pentyl, 2-hexyl, 2-heptyl, and 2-octyl were measured by an internal comparison method at 300°K. Activation to a level around 45 kcal mole−1 was by addition of H atom to the appropriate α-olefin. The validity of an assumption of invariance of thermochemical parameters, including the bond-dissociation energy D[3(—C)—(4—C)] for the higher members of the radical series, was established by measurements made with 5-Me-2-hexyl radicals. No evidence was found for any significant amount of H migration and isomerization of any of these excited radicals.
Together with earlier work, measurements now exist for the homologous series ethyl through 2-octyl radicals.
Theoretical rate constants agree well with the experimental values. Our earlier experimental verification for relatively smaller molecules that all vibrational and internal rotational degrees of freedom must be treated as active is now extended to the largest member of this series. Within the accuracy of the test provided by this work, intramolecular energy relaxation is also confirmed to be effectively random even for the highest member. The data illustrate the effect on rates of quantum-statistical weight changes due to structural increments in the series.
Secondary Isotope Effects on Amplitudes of Molecular Vibrations
Authors: Bartell L. S. 
Published: January 2005

Secondary isotope effects on amplitudes of bond oscillations in harmonically vibrating polyatomic molecules have been studied using normal coordinate theory. Morino's scheme for circumventing the L matrix by expanding the normal coordinate mean-square amplitude matrix in integral powers of the Λ matrix is extended and found to lead to some simple and useful inequalities. Upper and lower limits of bond amplitudes are established which are rigorously independent of masses of atoms other than the atoms in the bond. It is shown that the upper limit of secondary mass dependency vanishes with increasing temperature much more rapidly than does the primary mass dependency.
Even at absolute zero, secondary isotope effects on bond amplitudes are found to be relatively very much smaller than secondary isotope effects on bond frequencies. Numerical results of ``exact'' and various approximate approaches for calculating root-mean-square amplitudes are presented for the C–I bonds in CH3I and CD3I, and for the C=C bonds in C2H4 and C2D4. The smallness of secondary isotope effects on amplitudes indicates that their coupling with Morse bond asymmetry is not a major source of some recently reported secondary isotope effects on bond lengths.
On the Use of Double-Irradiation Methods for the Assignment of High-Resolution NMR Spectra with Repeated Spacings
Authors: Hoffman Ragnar A. , Gestblom Bo , Rodmar Sören , Forsén Sture 
Published: January 2005

An analysis of double-resonance experiments on pseudo-AX systems (i.e., pairs of doublets, the four transitions of which form a closed polygon in the energy-level diagram) based on the formalism of Freeman and Anderson, is presented.
Expressions are given for the transition frequencies and the transition probabilities in the general case. It is demonstrated that double irradiation may lead to the collapse of a repeated interval under comparatively general conditions and that double irradiation may alternatively lead to enlargement of the doublet splitting in spin systems which are not ideal for ``decoupling'' experiments.
The collapse or the enlargement of (repeated) doublet splittings may be used to establish the correct level arrangement in a general spin system. As illustrative applications of these methods, the ABX spectra of 5-methylthio-2-thiophenethiol and trans-cinnamaldehyde have been studied experimentally. In 5-methylthio-2-thiophenethiol selective ``decoupling'' and selective enlargement as well as general double irradiation experiments were performed and it was shown that the sign of the side-chain coupling JSH−3 is opposite to that of the ring-coupling constant J34. The implications of this result with regard to the mechanism of long-range thiol proton spin couplings are indicated.
In trans-cinnamaldehyde selective enlargement of an unresolved repeated spacing was produced in order to corroborate the earlier result that the two vicinal couplings in the side chain carry the same sign.
Recombination of Oxygen Atoms at High Temperatures as Measured by Shock-Tube Densitometry
Authors: Kiefer John H. , Lutz Robert W. 
Published: January 2005

The rate of recombination of oxygen atoms has been measured by shock-tube x-ray densitometry in the range 1500°—2800°K. Mixtures of ozone, oxygen, and argon or krypton were driven with helium in a shock tube and density records obtained for each experiment.
Within 2 μsec after the arrival of the shock wave the ozone had decomposed leaving an excess of oxygen atoms. The oxygen-atom concentration is subsequently determined by the density of the gas, and the recombination rate is obtained from the gradual decrease in density.
The reaction O+O+O2→ lim k42O2is the dominant reaction in this system, and its rate, defined by the equation d[O2]/dt=k4[O]2[O2] is found to be k4=(6.81±0.54)×108(2200/T)(1.22± 0.53) liter2/mole2·sec. This result is in close agreement with that found by Rink from dissociation experiments.
Use of 1s Gaussian Wavefunctions for Molecular Calculations. I. The Hydrogen Atom and the Hydrogen Molecule Ion
Authors: Sambe Hideo 
Published: January 2005

The 1s, 2s, 2p, 3s, 3p, 3dz, and 3dxy hydrogen-atom wavefunctions were expanded with linear combinations of 1s Gaussian functions of the form exp(—ar2), centered at different points in space to give the proper orbital symmetry. Energy values of −0.499999, −0.124630, −0.124947, −0.055170, −0.055460, −0.055450, and −0.055527 a.u. were found for 1s, 2s, 2p, 3s, 3p, 3dz, and 3dxy functions, respectively.
Trial functions for the 2Σg+ and 2IIu states of the hydrogen molecule ion were constructed from the 1s Gaussian expansion functions of 1s and 2p hydrogen-atom wavefunctions, introducing an effective charge and a polarization parameter which are closely related to the distortion of an atomic orbital in molecule formation. The trial functions, which have two nolinear parameters, give total energy errors of 0.055% and 0.16% at the equilibrium internuclear distance for the 2Σg+ and 2IIu states, respectively, of the hydrogen molecule ion.
The extension of this procedure to polyatomic molecules is discussed, and the simplicity of the required integrals and the small number of nonlinear parameters for the procedure are emphasized.
Thermal Decomposition of ClCN
Authors: Schofield David , Tsang Wing , Bauer S. H. 
Published: January 2005

The thermal decomposition of cyanogen chloride was studied in a shock tube, using specific absorption spectroscopy to follow the concentration of CN radicals as a function of time behind the shock wave. This investigation is similar to the previously studied dissociation of cyanogen, but the kinetics are much more complex because of the possibility of reactions involving the unlike radicals CN and Cl.
A mechanism involving six reactions is proposed; these account for all features which characterize the observed results. Values for some ratios of rate constants have been obtained by direct analysis of the CN absorption curves. A method of trial curve fitting using a digital computer was used to deduce the absolute values of the rate constants for the important steps.
Barrier Studies in the Halopropenes. I. The Microwave Spectrum, Barrier to Internal Rotation, Quadrupole Coupling Constants, and Microwave Double-Resonance Spectra of 2-Chloropropene
Authors: Unland M. L. , Weiss V. , Flygare W. H. 
Published: January 2005

The microwave spectra of CH3C35Cl:CH2 and CH3C37Cl:CH2 have been observed in the ground and first excited torsional states. The ground-state rotational constants of CH3C35Cl:CH2 are A=9272.79±0.10 Mc/sec, B=4983.84±0.10 Mc/sec, and C=3304.39±0.10 Mc/sec. The ground-state rotational constants for CH3C37Cl:CH2 are A=9272.31±0.10 Mc/sec, B=4850.48±0.10 Mc/sec, and C=3245.11±0.10 Mc/sec. The quadrupole coupling constants along the appropriate principal inertial axes in the ground torsional state of CH3C35Cl:CH2 are χaa=−68.15±0.10 Mc/sec, χbb=37.11±0.10 Mc/sec, and χcc=31.04±0.10 Mc/sec. The quadrupole coupling constants for CH3C35Cl:CH2 in the excited torsional state were within the experimental error of the corresponding ground-state values. The quadrupole coupling constants in CH3C37Cl:CH2 are χaa=−53.80±0.10 Mc/sec, χbb=29.30±0.10 Mc/sec, and χcc=24.50±0.10 Mc/sec. Analysis of the first excited-torsional-state rotational spectrum yielded a barrier to the internal rotation of the methyl group of 2671±20 cal/mole.
Microwave double-resonance experiments were used to provide a positive confirmation for the assignments of the 000→101 and 101→202 transitions in CH3C35Cl:CH2 as well as exhibiting some interesting features in the energy levels involved in the transitions. Two types of experiments were performed. The first experiments involved irradiating the quadrupole components in the 000→101 transition while observing the 101→202 transition. The second set of experiments involved irradiating one of the quadrupole components in the 000→101 transition and using a second klystron to observe the entire 000→101 triplet.
Effect of Electric Fields on the Radiation-Induced Reaction between Carbon Dioxide and Graphite
Authors: Watanabe Tsutomu , Matsumura Hisao , Washino Masamitsu , Natori Makoto 
Published: January 2005

The effect of an electric field on the γ-ray-induced reaction of CO formation from CO2 and graphite was investigated. The experiment was carried out at room temperature under an exposure dose rate of 1.5×105 R/h using diodelike tubes with graphite and metal (tungsten or molybdenum) electrodes filled with CO2 gas at 300 mm Hg. When a negative voltage was applied to the graphite to obtain a saturation current, the yield of CO was about 2.5 times as much as that in the absence of any field. However, on application of a positive field, the yield was not significantly different than the zero field case. The G value for CO formation was found to be 0.62∼1.01 in the absence of the field.
The ionic reaction mechanisms CO2++C−(graphite electrode)→2COand/or CO2++C−(graphite electrode)→C(graphite)O+COare proposed for the increased yield of CO in the case of negative voltage application to the graphite.
Radiolysis of Ethylene. IV. Unimolecular Dissociation of Intermediate Ion—Molecule Complexes
Authors: Meisels G. G. 
Published: January 2005

Kinetic analysis of free-radical reactions in the radiolysis of ethylene demonstrates that the relative extent of radical addition to ethylene can be held constant by maintaining the ratio of accelerator beam current to ethylene pressure invariant. The pressure dependence of the methane and methyl radical yields when this ratio is constant reveals that the mechanism of their formation includes competition between unimolecular dissociation of an intermediate ion and its participation in an ion—molecule reaction. Consideration of known ion—molecule reactions suggests that the species involved in the competing steps are [C6H11+] (methane formation) and [C6H12+] or [C4H8+] (methyl radical formation). Rate constants of 4.2×108 and 1.0×109 sec−1, respectively, are calculated for the dissociation processes on the basis of collision efficiency for the competing ion—molecule reactions.
About one-fourth of the methane and one-half of the methyl radicals are formed by reactions which are independent of pressure below 1 atm. This may be ascribed to rate constants larger than 1010 sec−1 for dissociation of [C8H15+] and [C8H16+] ion, respectively, or to the existence of at least two discrete energy levels for the dissociating species. Relative dissociation probabilities of intermediate ion—molecule complexes, determined by mass spectrometry, are used to estimate G(C2H4+) ≈ 1.5 and G(C2H3+) ≈ 1.0 ions/100 eV at approximately atmospheric pressure, in good agreement with values of 1.51 and 0.96, respectively, which may be calculated from W and fragmentation patterns for 70-eV electrons.
Variation-Perturbation Approach to Electron-Cluster Wavefunctions
Authors: Stanton Richard E. 
Published: January 2005

Sinanoğlu's cluster expansion formula for the exact wavefunction of a many-electron system is investigated by variation-perturbation techniques. The perturbation operator is the difference between the actual Hamiltonian and a symmetric sum of arbitrary one-electron Hamiltonians. Each perturbation function is then expanded in accordance with the cluster formula.
When the occupied orbitals are chosen to be eigenfunctions of the one-electron Hamiltonian the variational equations determining different nth-order clusters are completely independent. If the orbitals are unitarily transformed to achieve greater localization the variational equations for each cluster are coupled.
The perturbation governing first-order two-electron clusters has the form of a dipole potential. This result does not depend on the nature of the one-electron Hamiltonian. It is primarily useful, however, in studying the question of interorbital vs intraorbital correlation, i.e., when the one-electron Hamiltonian is the Hartree—Fock operator. It is shown that interorbital correlation is small if the Hartree—Fock orbitals are well separated. The advantage of transforming to localized orbitals is shown to be questionable because of the coupling between the clusters.
Differential equations governing first- and second-order orbital correction functions are derived and partially interpreted. In accordance with Brillouin's theorem the first-order corrections vanish as the one-electron Hamiltonian approaches the form of the Hartree—Fock operator. In the Hartree—Fock case the role of the second-order orbital correction functions is to relax the charge density subsequent to correlation. An investigation of the derivative of the correlation energy with respect to nuclear charge, a one-electron property, suggests that the second order correction functions may be important whenever it is necessary to evaluate one-electron properties to an accuracy beyond the Hartree—Fock estimate.
The second order four-electron cluster is shown to be exactly expressible as a sum of products of first-order two-electron clusters.
Explicit variational equations are derived also for the second-order two- and three-electron Hartree—Fock clusters.
Electron Spin Resonance Study of Irradiated Anhydrous Maltose
Authors: Herak J. N. , Adamič K. , Blinc R. 
Published: January 2005

The electron spin resonance spectra of γ-irradiated powdered anhydrous α-maltose have been measured. By temperature annealing it has been found that:
(a) The room temperature ESR spectrum consists of at least three different types (A, B, C) of radiation-induced damage centers.
(b) Type A centers seem to result from a rupture of the C-1—H bond. They transform into Type B centers with a half-life of about 110 min (in air at room temperature). The most probable type of transformation seems to be a change in configuration of the pyranose ring.
(c) Whereas Type B centers recombine under the above conditions with a half-life of about 26 h, the half-life of Type C centers exceeds a month. There are some indications that Type C centers are connected with a breaking of the glycosidic bond between two pyranose rings.
Microwave Spectrum and Structure of Nitric Acid
Authors: Cox A. Peter , Riveros José M. 
Published: January 2005

The microwave spectra of five further isotopic species of nitric acid, H18ONO2, cis-HON18OO, trans-HONO18O, cis-HO15N18OO, and D15NO3, have been investigated. The data have been used to refine the previous structural determination of Millen and Morton. In the calculation of structure, particular consideration has been given to the use of ground-state moments of inertia in Kraitchman's equations for near-oblate planar molecules. The structure was calculated using several different methods, including the double-substitution method due to Pierce, in order to substantiate the following structural parameters: O–H=0.964, (H)O–N=1.406, cis–N–O=1.211, trans-N–O=1.199 Å, ∠HON=102°9′, ∠cis-ONO=115°53′, ∠trans-ONO=113°51′, and O···O (NO2 group)=2.184 Å.
This determination clearly demonstrates a 2° tilt of the NO2 group away from the hydrogen atom. The NO2 parameters are close to those found in a number of related molecules, but there is some evidence that the cis-NO bond in HNO3 is slightly longer than the trans-NO bond. The NOH configuration is very similar to that found in formaldoxime.
Further evidence for the exact planarity of nitric acid is given. Stark-effect measurements limit the out-of-plane component of the dipole moment μC to a value less than 1.1×10−3 D. The other components have been redetermined to have the values μA=1.99 D and μB=0.88 D, giving a total dipole moment μ=2.17±0.02 D.
On the Distribution of Small Radii of Gyration of Linear Flexible Polymer Molecules
Authors: Forsman W. C. 
Published: January 2005

The Fourier transform of the distribution function characterizing the three orthogonal components of the radius of gyration of linear flexible polymer molecules can be obtained from the properties of random-flight chains. In this publication we present a detailed analysis of the problem of inverting the Fourier transform of the distribution of small radii of gyration and present approximate and asymptotic expressions for the distribution. We consider random-flight chains of t statistical links. If we measure a given orghogonal component of the radius of gyration Si by the dimensionless parameter ξ=π(12)−12Si/〈Si2〉12, we find:
(1) In the domain of ξ between about (1/√3) and (3/t½), the distribution of ξ is adequately approximated by Wξ(ξ)=(π32)2−1ξ−3 exp (−π2/16ξ2). The expression is independent of t and therefore, as for larger radii, independent of how we subdivide a real polymer molecule into statistical segments. We also conclude, then, that for all radii such that ξ≥(3/t12), Wξ(ξ) is independent of the detailed structural features of real polymer chains.
(2) In the domain of ξ⩽(1/102t12) the distribution of ξ can be approximated by Wξ(ξ)=[2t!/(12t−1)!]ξt−1. The configurational statistics of such highly compressed coils is dependent on the number of statistical chain elements and thus on how we would choose to subdivide a real polymer molecule into such elements. We can also interpret these results to imply that the configurational statistics of such highly compressed real polymer molecules would be dependent upon the detailed structural features of the chain.