bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport Properties of a Gas of Diatomic Molecules
Authors: Curtiss C. F.
Published: February 2004

Explicit expressions, valid in the classical limit, are derived for the rotational relaxation time and viscosity of a low-density gas of rotating, nonvibrating, diatomic molecules. These expressions are based on the quantum mechanical expressions in terms of the degeneracy-averaged cross sections for a gas in which the average angular momentum of the molecules is zero. The use of an expression for the classical limit of the degeneracy-averaged cross section leads to the evaluation of several of the summations and integrations.
On the Critical Region of a Simple Fluid. II. Scaling-Law Equation of State
Authors: Stephenson John
Published: February 2004

The scaling-law equation of state is used to illustrate some consequences of the elementary index inequalities β + γ− > 1 > α− + β. It is shown that (∂2P / ∂T2)V evaluated on the phase boundary below Tc from the homogeneous-phase side diverges with index (α + β), where α is the (scaling-law) index for CV=Vc. Also, it is shown that CP=Pc diverges with index [1 − (1 / δ)] on the critical isobar, where δ is the degree of the critical isotherm.
Electronic Specific Heats of Alloys of the MgCu2−xZnx System
Authors: Bechman Charles A. , Craig R. S.
Published: February 2004

Specific-heat measurements were made on 17 alloys of the pseudobinary system MgCu2−xZnx between 1.5 and 4.2°K. In addition to the two terminal phases MgCu2 and MgZn2, the compositions studied included nine alloys having the cubic MgCu2 structure, four having the hexagonal MgZn2 structure, and two samples consisting of a mixture of two phases. The density of states at the Fermi level N(EF) was calculated from the measured values of γ. The variation of γ with composition is compared with results from this laboratory previously reported on the MgCu2−xAlx and Mg2−xSix systems. Variation of γ with composition in the cubic range exhibited, qualitatively, the same trends that were shown in the MgCu2−xAlx system, namely, a maximum in γ at 1.44 electrons/atom, a rapid decrease in γ as the stability limit for the cubic phase at ≈ 1.73 electrons/atom is approached, and a shoulder on the falling curve at 1.59 electrons/atom. Values of the Debye θ, calculated from the slopes of the curves of C / T vs T2 are computed for the three systems.
Optical Absorption Characteristics and Photobleaching Behavior of Trapped Electrons in γ-Irradiated Alkaline Ice
Authors: Hase Hirotomo , Kevan Larry
Published: February 2004

Trapped electrons, et−, are produced by γ irradiation of alkaline ice (10M NaOH) at 77°K. The et− absorption band maximum at 590 nm shifts to shorter λ for bleaching at 700 nm and shifts to longer λ for bleaching at 400 nm. After partial bleaching, electrons can be shifted back and forth between traps characterized by long and short λ. Although this suggests at least two trap depths, there is probably a broad spectrum of trap depths. The quantum efficiency, φ, for photobleaching et− is 0.15 and independent of λ when the optical density is measured at 590 nm. For the optical density measured at the bleaching wavelength, φ increases to 0.52 at 400 nm and to 0.26 at 700 nm; φ also increases in the presence of electron scavengers. φ decreases as the fraction of et− bleached, F, increases and follows φ = 0.15 exp( − 3.7F) for F = 0–0.85. All of these changes are explained by retrapping and trap interconversion. φ is also independent of temperature between 4 and 77°K in agreement with photoconductivity measurements. ε(590 nm) = 1.94 × 104M−1·cm−1, and the oscillator strength is ≥ 0.86 for the et−band.
Infrared Spectrum and Structure of the Species CO3
Authors: Jacox Marilyn E. , Milligan Dolphus E.
Published: February 2004

Upon photolysis of solid CO2 by 1216-Å radiation, very high yields of CO3 have been obtained. There is no evidence for the production of hydrogen-containing species in experiments in which photolytically produced H or D atoms are also present. Experimental evidence supports a C2υ structure for CO3 in its ground state, as predicted by molecular orbital calculations. The vibrational frequency pattern for the planar modes of isotopically substituted species of CO3 has been fitted to a valence force potential having a minimal number of interaction force constants, assuming both an open structure having an O–C–O angle of 80° and a three-membered ring structure having an O–C–O angle of 65°. Although the force constants obtained for the ring structure appear to be quite reasonable, exceptionally large values have been obtained for the O–C–O bending force constant and for all of the interaction constants for the open structure. On this basis, the three-membered ring structure is favored for CO3 in its ground state.
Infrared Spectrum and Structure of Intermediates in the Reaction of OH with CO
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

Upon vacuum-ultraviolet photolysis of H2O in a CO matrix at 14°K, infrared absorptions of HCO, H2CO, HCOOH, and CO2 become prominent. Furthermore, new absorptions due to reactive product species appear at 615, 620, 1077, 1088, 1160, 1261, 1797, 1833, 3316, and 3456 cm−1. These absorptions diminish in intensity when the sample is subjected to radiation in the 2000–3000-Å spectral range. Detailed consideration of the processes which may occur in this system and extensive isotopic substitution studies support the assignment of these absorptions to the cis and trans stereoisomers of H–O–C=O, produced by the reaction of OH with the CO matrix. Valence force potentials having only small contributions from interaction terms have been found which correspond to a physically reasonable vibrational assignment and which satisfactorily reproduce the pattern of observed frequencies for the various isotopic species of both cis- and trans-HOCO. Evidence suggests that cis- and trans-HOCO photodecompose to produce H atoms and CO2.
Electronic Structures of Linear Polymers. II. Formulation and CNDO/2 Calculation for Polyethylene and Poly(tetrafluoroethylene)
Authors: Morokuma Keiji
Published: February 2004

The Hartree–Fock procedure for infinite linear polymers is formulated by the use of the cyclic boundary condition. An actual calculation using this procedure is carried out for the various conformations of infinite polyethylene and poly(tetrafluoroethylene) in the semiempirical CNDO/2 SCF approximation. Polyethylene has an energy minimum at the C–C rotational angle ω = 180° or for the trans zigzag conformation, while poly (tetrafluoroethylene) has a minimum around ω = 162°, a slightly twisted trans zigzag conformation. Both are in excellent agreement with experimental results for the single crystals. Both polymers, experimentally good electric insulators, are calculated to have a large energy gap between the highest-filled and the lowest-vacant band. The segmental and atomic energy contributions and charge distributions are discussed in detail in comparison with alkanes and as functions of the conformational angle ω.
Microwave Induced Time-Dependent Effects in Triplet Phosphorescence
Authors: Harris C. B.
Published: February 2004

The changes in the polarization and intensity of phosphorescent emission from triplet states, induced by a resonant time dependent microwave field coupling magnetic sublevels, are described in the absence of spin–lattice relaxation. Specifically, the microwave field can be used to amplitude modulate the polarization and intensity of phosphorescence from organic molecules or to rotate the polarization vector of phosphorescence. In addition, “optical phase precession,” a phenomenon closely resembling quantum beats, is predicted. Finally, the use of adiabatic inversion of the magnetic sublevel populations to directly measure intersystem crossing is demonstrated.
Mean Radiative Lifetime of Vibrationally Excited (υ = 9) Hydroxyl. Rate of the Reaction of Vibrationally Excited Hydroxyl (υ = 9) with Ozone
Authors: Potter A. E. , Coltharp R. N. , Worley S. D.
Published: February 2004

The mean radiative lifetime of vibrationally excited (υ = 9) ground-state hydroxyl was measured in a fast-flow system. Excited hydroxyl was generated by reaction of H with O3 at the entrance of a flow tube, and the decay of 2.15-μ radiation from the OH (9–7) band was measured down the tube. After correcting the decay rate for wall quenching and reaction with ozone, the lifetime was found to be (6.4 ± 1.4) × 10−2 sec. The effect of ozone concentration on the decay rate yielded a rate constant of (7.7 ± 0.3) × 10−12 cm3 molecule−1·sec−1 for the reaction of OH (υ = 9) with O3.
Vibrational Raman Spectra of CaMoO4 and CaWO4 at High Pressures
Authors: Nicol Malcolm , Durana Jean F.
Published: February 2004

Raman vibrational spectra at pressures as high as 40 kbar are reported for the scheelite and previously unknown high-pressure phases of CaMoO4 and CaWO4. The pressure derivatives of the vibrational frequencies, dν / dP, are all between 0.0 and 1.0 cm−1·kbar−1 which is normal for ionic crystals; however, the observed pressure dependences of the frequencies of the internal modes are qualitatively different from those predicted according to Scott's interpretation of the splittings of the scheelite spectra. The appearance of the high-pressure phases is indicated by splittings of Eg modes at 145 and 797 cm−1 in CaMoO4 and 117 and 797 cm−1 in CaWO4. The spectra of the high-pressure phases and the dependences of the apparent transition pressures upon orientation of the crystallographic axes relative to the small stress anisotropy in the high-pressure cell suggest that the high-pressure phases have structures similar to that of NiWO4.
Time Lag and Fluctuations in Diffusion through an Inhomogeneous Material
Authors: Frisch H. L. , Prager Stephen
Published: February 2004

It is shown that the time lag for diffusion through a slab of inhomogeneous material can be expressed in terms of the steady-state concentration distribution. This result is used to calculate the time lag in a laminated slab and to obtain bounds on the time lag in slabs with arbitrary inhomogeneities.
Methanol: Heat Capacity, Enthalpies of Transition and Melting, and Thermodynamic Properties from 5–300°K
Authors: Carlson H. G. , Westrum Edgar F.
Published: February 2004

Thermal properties of methanol were studied by adiabatic calorimetry. The first-order nature of the phase transition at 157.4°K with an entropy increment of 0.97 cal mole−1·°K−1 was confirmed. The heat capacity of the crystalline phase stable just below the triple point was defined and shown to be extremely sensitive to impurity. No evidence for a second previously-reported phase transition could be detected. The standard entropy (S°) and Gibbs energy function (− [G° − H°0] / T) for the liquid at 298.15°K are 30.40 and 15.18 cal mole−1·°K−1, respectively. The proposed classification of methanol as a plastic crystal on the basis of its small entropy of melting (4.38 cal mole−1·°K−1) is considered with respect to hydrogen bonding in the liquid phase.
Optical Absorption Spectra of Gd3+:LaF3 and GdCl3·6H2O
Authors: Carnall W. T. , Fields P. R. , Sarup R.
Published: February 2004

The absorption spectra of single crystals of Gd3+:LaF3 and GdCl3·6H2O were examined at low temperatures and high resolution. Stark components belonging to the G6 multiplet near 50 000 cm−1 were observed in both matrices. Theoretical treatment of the data confirmed the importance of including two-body magnetic interactions in the analysis.
Kinetics of Iodine Atom Recombination between 300 and 1164°K
Authors: Blake J. A. , Burns George
Published: February 2004

The recombination of iodine atoms in the presence of argon and I2 has been studied between 300 and 1164°K. The rate constants, krAr and krI2, are (in liters2 mole−2·second−1) Temperature (°K)29847357386410641164krAr × 10−8248.76.64.84.14.4krI2 × 10−101401160.9 At 1064°K, the rate constants krI2 and krI were estimated to be equal to or less than 10krAr. These results were interpreted in terms of the radical–molecule complex (RMC) mechanism [J. K. K. Ip and G. Burns, J. Chem. Phys. 51, 3414 (1969) and J. A. Blake, R. J. Browne, and G. Burns, J. Chem. Phys. 53, 3320 (1970)]. This mechanism predicts that the interaction potential between an iodine atom and an argon atom is four to nine times deeper than the potential between argon and xenon, which is iodine's neighbor in the periodic table. The potential depth for the I–Ar complex was estimated to be between 1.2 and 2.8 kcal/mole, depending upon which assumptions were used in the RMC mechanism. The interaction potential between I and I2 was estimated to be 5.5 kcal/mole deep. The present calculations suggest that the three-body reaction probabilities for 2I+Ar→I2+Ar reaction are in the range between 0.2 and 0.02, dependent upon assumptions used in the RMC mechanism. Although the RMC mechanism yields a satisfactory agreement with the experiment, at highest temperatures, the “energy-transfer” mechanism, I+I⇋I2*, I2*+Ar→I2+Ar, appears to contribute to the over-all recombination. At 1064°K, approximately one-quarter of recombination seems to proceed by this route. Present recombination rate data overlap the shock wave dissociation rate data by some 300°C. Above 1000°K, the recombination rate constants calculated from shock wave data are generally higher, and display a steeper negative temperature dependence, than the flash photolysis recombination rate constants, obtained at the same temperature. These discrepancies display a pattern similar to those already reported for bromine [J. K. K. Ip and G. Burns, J. Chem. Phys. 51, 3425 (1969)] and chlorine [G. Burns and R. J. Browne, J. Chem. Phys. 53, 3318 (1970)]. An analysis of thermal effects, which are unimportant at room temperature, but tend to dominate recombination above 1000°K, is also given.
Analytic Sutherland Model Radial Distribution Function
Authors: Chen Chimin T.
Published: February 2004

Using the weak-attraction approximation of the Sutherland (∞, 6) potential, the analytic forms of g1(r, T), which is the coefficient of the linear density term in the expansion of the radial distribution function g(r, ρ, T) in powers of the density ρ, are obtained with and without the correction for the triple–dipole interaction. Neglecting ρ2 and higher terms, the radial distribution functions of Ar are evaluated for states in the neighborhood of the critical point. The calculated locations of the first minimum in the radial distribution function and the first coordination numbers are in good agreement with the experimental results of Mikolaj and Pings. The agreement of the locations of the first minimum of the function 4πr2ρg(r) is only fair.
Equilibrium Thermodynamic Properties of the Mixture of Hard Spheres
Authors: Mansoori G. A. , Carnahan N. F. , Starling K. E. , Leland T. W.
Published: February 2004

An equation of state is proposed for the mixture of hard spheres based on an averaging process over the two results of the solution of the Percus–Yevick integral equation for the mixture of hard spheres. Compressibility and other equilibrium properties of the binary mixtures of hard spheres are calculated and they are compared with the related machine-calculated (Monte Carlo and molecular dynamics) data. The comparison shows excellent agreement between the proposed equation of state and the machine-calculated data.
Spectra and Structure of Small Ring Compounds. XX. Fluorocyclobutane
Authors: Durig J. R. , Willis J. N. , Green W. H.
Published: February 2004

The infrared spectrum of fluorocyclobutane vapor has been recorded from 4000–33 cm−1. The infrared spectrum of the solid at − 196°C has been recorded from 4000–200 cm−1. The Raman spectra of the liquid at room temperature and the solid have been recorded and depolarization values have been measured. The spectra have been interpreted on the basis of a puckered model ring with only one conformation which has a plane of symmetry and belongs to the Cs point group. Assignment of the 30 normal vibrations has been based on depolarization values, band contours, group-frequency correlations, and relative intensities. A series of four Q branches was observed in the far-infrared spectrum and has been interpreted as arising from the fundamental and “upper-state” transitions of the anharmonic ring-puckering vibration. The series could be fit equally well by two different double-minima potential functions, one with a relatively high barrier of 803 cm−1 and the other with a 485-cm−1 barrier. On the basis of previous microwave data and the midinfrared and Raman spectra of the solid and fluid states, the higher barrier potential is believed to more nearly describe the actual potential function governing the ring-puckering vibration; the energy difference between the two conformations was calculated to be 722 cm−1.
Nuclear Magnetic Resonance Study of Tetrafluoro-1,3,-Dithietane in an Isotropic and a Lyotropic Liquid Crystalline Medium
Authors: Long Robert C. , Goldstein J. H.
Published: February 2004

Fluorine magnetic resonance experiments on tetrafluoro-1,3-dithietane (F4C2S2) in a lyotropic mesophase show conclusively that the molecule possesses D2h symmetry. Analysis of 19F spectra in the nematic mesophase over a range of temperatures from 299–321°K indicate that the anisotropic contribution to the spin–spin coupling constant is negligible. From the observed spectra it is impossible to determine all bond distances. However, assuming a C–F distance of 1.334 Å and a C–C distance of 2.413 Å, an FCF angle of 109.2° ± 0.5 can be calculated. In addition, high-resolution spectra have been obtained for both the 13C nuclei and 13C–F satellites in the isotropic phase. The geminal F–F coupling is found to be +137.06 Hz. Although the 13C and 13C–F satellite spectra in isotropic media are insensitive to permutation of the cis and trans F–F couplings, the nematic phase results permit the unambiguous assignment of the smaller coupling to the cis arrangement. The variation of the motional constants with temperature, the determination of the absolute signs of spin–spin coupling constants, and anisotropy in the chemical shift are discussed.
Quantum Calculations of Collinear Reactive Triatomic Systems. II. Theory
Authors: Miller G. , Light J. C.
Published: February 2004

Using reaction coordinates, we develop a general method to calculate quantum mechanically the reactive and nonreactive scattering probabilities for a collinear collision of an atom and a diatomic molecule. This method offers increased flexibility over previous methods, in that a much wider variety of potential surfaces may be investigated in a much faster scheme of solution.
Kinetics and Thermodynamics of the CN Molecule. II. The Dissociation of C2N2
Authors: Slack M. W. , Fishburne E. S. , Johnson A. R.
Published: February 2004

A shock tube investigation of the dissociation of cyanogen diluted in argon is described. Dissociation rate coefficients for the reaction, C2N2+M→CN+CN+M, were obtained behind the incident shock wave over the temperature range 2700–4000°K and for mixtures containing from 0.05%–1.0% C2N2. The rate coefficients were best fitted by the expression, kD = 4.58 × 1014exp(− 69 kcal/RT) cc mole−1·sec−1. The current measurements were in good agreement with the lower temperature data of Tsang et al. and the combined data may be summarized by kD = 3.71 × 106 T1/2(E / RT)8exp(− E / RT) cc mole−1·sec−1 over the temperature range 1750–4000°K, where E = 128.7 kcal/mole.
Sulfur-33 Hyperfine Interactions in the Gas-Phase Electron Resonance Spectra of Π 2SH and Δ 1SO
Authors: Miller Terry A.
Published: February 2004

The gas-phase electron resonance spectra of Δ 331SO and Π 332SH have been observed in natural abundance. Since 33S has a nuclear spin of 32, the observed spectra have rich magnetic hyperfine and electric quadrupole structure. This structure has been analyzed to determine the following magnetic hyperfine and quadrupole constants: for Π 332SH—A1 = 71.1 ± 1.0 MHz, e2q0Q = 13.5 ± 2.0 MHz; for Δ 331SO—a = 145.1 ± 3.0 MHz, where the symbols are defined in the text. The Δ 331SO results are compared in a detailed way to similar hyperfine measurements in the Σ3 ground state of 33SO. The Π 332SH measurements are compared with the predictions of Hartree–Fock calculations on the ground state of SH.
Thermomagnetic Torque in Deuterium Gas
Authors: McClurg G. R. , Adair T. W.
Published: February 2004

The Scott thermomagnetic torque has been measured in three ortho–para concentrations of deuterium gas at pressures of 0.45–1.80 torr and in magnetic fields up to 440 Oe. The temperature range covered was 100–350°K. The product of the torque and pressure plotted as a function of the field divided by pressure has a maximum at (H / P)max = 90 Oe/torr. All ortho–para concentrations of deuterium gas produced the same torque in contrast to the results in hydrogen. Also, in all concentrations the torque was found to become very small as the temperature was lowered to 100°K.
Luminescence from Thin Solid Films at 77°K under Low-Energy Electron Bombardment
Authors: Merkel Paul B. , Hamill William H.
Published: February 2004

A spectrometer system for the study of luminescence from thin solid films induced by low-energy electron bombardment is described. This technique shows promise in the study of higher energy and optically forbidden electronic transitions in parent molecules and in providing information concerning radiolytic products. Films of benzene and toluene exhibit monomer fluorescence onsetting at an excitation energy of 4.5 eV. In the case of toluene luminescence from the benzyl radical also appears. Benzene phosphorescence is observed in a cyclohexane matrix. For cyclohexane and n-hexane films, fluorescence is observed with maxima at approximately 200 and 210 nm, respectively. At impact energies above about 15 eV other emission bands appear in the alkanes which may involve excited radicals and ions. Water exhibits bands with λmax at 280 and 380 nm. The former is attributed to fluorescence of the hydroxyl radical, and the latter can plausibly be assigned to phosphorescence from either the quartet state of the OH radical or from triplet water.
Lifetimes and Self-Quenching Cross Sections of Vibrational Levels in the B State of Bromine Excited by a Tunable Dye Laser
Authors: Capelle Gene , Sakurai Katsumi , Broida H. P.
Published: February 2004

A tunable dye laser was used to excite selected vibrational levels between υ′ = 1 and 31 of the B 3Π0u+ state of Br2. Lifetimes and self-quenching cross sections were measured by observing the direct decay of fluorescence as a function of pressure. Large variations of lifetimes and cross sections were found; the lifetimes varied by a factor of 8, ranging from greater than 1.2 μsec near υ′ = 27 to less than 0.15 μsec near υ′ = 14. Two minima of lifetimes near υ′ = 1 and 14 can be explained by decay of the B state by means of spontaneous predissociation through dissociative states.
Curve Crossing in Collisional Dissociation of Alkali Halide Molecules
Authors: Ewing J. J. , Milstein Richard , Berry R. Stephen
Published: February 2004

The primary dissociation step for alkali halide diatomics in argon has been studied in order to determine whether collisional dissociation produces ions, atoms, or a mixture of both types of products. The method is based on time-resolved absorption spectroscopy of shock-heated vapors. Results show that the cesium halides, and the rubidium and potassium halides, with the exception of the two iodides, dissociate essentially completely to ions; that the lithium salts and NaI and NaBr dissociate essentially completely to atoms; and that the other alkali halides (KI, RbI, NaCl, and probably NaF) dissociate to mixtures of atoms and ions, at least under some conditions. The branching ratio of atom pairs/ion pairs is interpreted in terms of the effective width of the adiabatic dissociation channel, compared with the spacing of the vibrational levels of the diabatic bound state.
Theoretical Electronic Transition Probabilities in Diatomic Molecules. I. Hydrides
Authors: Henneker W. H. , Popkie H. E.
Published: February 2004

Hartree–Fock (HF) electronic transition moments calculated in both the position and momentum representations are presented as a function of the internuclear separation R for the BeH, MgH, OH, and SH (A–X) systems. The vibrational averages of these quantities are obtained and the results are used to calculate some absorption band oscillator strengths. For the OH (A–X) system several independent experimental determinations of the 0–0 band oscillator strength have been reported in the literature. Our theoretical value of 20.6 × 10−4 differs from experiment by a factor of 2.5. Active electron and virtual orbital approximations to the HF transition moment integrals are given. Consideration of the united and separated atom limits and the region of the equilibrium internuclear separation for the states involved leads to an abbreviated discussion of the effect of correlation on the HF transition moments. HF transition moment calculations at a single value of R are also reported for the BH+, AlH+, HF+, and HCl+ (A–X) systems.
Light Scattering and the Coupling of Molecular Reorientation and Hydrodynamic Modes
Authors: Keyes Thomas , Kivelson Daniel
Published: February 2004

A statistical theory, based on linear response theory, is presented to describe the coupling between molecular reorientation and both longitudinal and shear hydrodynamic modes in liquids, and the effect of this coupling on the depolarized light scattering spectrum. The theory is valid if molecular reorientation takes place by rotational diffusion. The “doublet” features of the observed spectra are explained and both the VH and HH depolarized spectra can be understood in terms of one nonhydrodynamic parameter which depends upon the anisotropic intermolecular potential. Although the longitudinal modes contain traveling waves which couple to the molecular reorientation and give rise to depolarized Brillouin doublets, the doublet due to the coupling to the shear modes arises from purely dissipative motion and not from shear waves.
Inelastic Nonreactive Scattering; Three Atoms Interacting via Three Interatomic Potential Energies
Authors: Locker David J.
Published: February 2004

The pioneering calculations of Shuler and Zwanzig imposed many constraints on three-body scattering. Their computations applied to systems interacting collinearly and having an interaction potential energy such that V = 0 for intermolecular separations greater than some finite value σ and V = ∞ for separations less than or equal to σ. In their studies of atom–diatomic molecule collisions the incident atom was chosen to interact only with the nearest atom of the diatomic molecule. Cheung and Wilson extended the Shuler and Zwanzig procedure in order to study systems interacting via structured interaction potential energies which are represented by a series of finite steps. In the latter work, however, the intermolecular interaction was again chosen to be between nearest atoms. In the present work expressions are generated which represent an incident atom interacting with both atoms of a diatomic molecule. Two interaction potential energies are described. In one case the incident atom acts upon both atoms of the diatomic molecule via a hard-core interaction. For this case, calculations are carried out yielding results which are generally in agreement with the results of Shuler and Zwanzig. In another case the interactions are each represented by a single step. The present discussion may be extended to examine multistep interactions.
Solvent Effects on Electronic Spectral Intensities
Authors: Linder Bruno , Abdulnur Suheil
Published: February 2004

A theory is developed for determining the effect of the London–van der Waals interaction on the electronic spectral intensities of an absorbing substance dissolved in a transparent solvent. The formulation is based on quantum-statistical double perturbation theory: time varying in the applied field and time independent in the intermolecular force field. A virial expansion is developed for the extinction coefficient, integrated over a band, in terms of molecular parameters and molecular distribution functions, and the first and second virial coefficients are worked out in detail. It is shown that the leading term produces the oscillator strength of the free absorbing molecule in a rarefied gas. The results are analyzed in terms of local field contributions and distortions of electron distributions by the surroundings. The relevance of the theory to allowed transitions and forbidden transitions made allowed is discussed.
The CO2 Photolysis Problem
Authors: Slanger Tom G. , Black Graham
Published: February 2004

The photolysis of CO2 has been investigated at 1470 Å to determine the O(1D) quantum yield and the subsequent O(3P) yield resulting from O(1D) deactivation, the O(1D)–CO2 interaction rate constant, and the possible role of CO3 in the over-all process. Utilizing the 1302–1306-Å Oi triplet as a resonance fluorescence source, O(3P) atoms were monitored during O2 and CO2 photolysis. By measuring both the intensity and decay time constants for the fluorescence, it could be concluded that each photon absorbed by CO2 ultimately resulted in an O(3P) atom. This observation suggests that all previous determinations of low O2/CO ratios in CO2 photolysis relate to effects taking place after O(3P) has been produced, and it is quite likely that wall absorption of O(3P) is the dominant process. By utilizing competitive quenching between CO2, H2, and N2, it was determined that the O(1D) quantum yield is unity, and that the rate constant ratio for O(1D) deactivation by N2 and CO2, kN2 / kCO2, is 0.26, in excellent agreement with other investigations, giving a CO2 rate constant of 3 ± 1 × 10−10 cm3 molecule−1·sec−1. Attempts to find effects attributable to CO3 participation in the system were unsuccessful, and the implications for planetary atmosphere models are discussed.
ESR Study of the Sugar Radical in Irradiated Deoxyadenosine
Authors: Alexander Chester , Franklin Carl E.
Published: February 2004

Single crystals of deoxyadenosine monohydrate grown from H2O and D2O solutions have been x irradiated and studied by electron spin resonance techniques at room temperature. The results show an isotropic coupling of 7 ± 1.0 G to one β proton and an anisotropic coupling of an α proton with principal values − 22.6 ± 0.5 G, − 16.4 ± 0.5 G, and − 5 ± 0.5 G. The spin density on the carbon atom (C5′), calculated from the above results, is 0.64. The g-tensor principal values are 2.0029 ± 0.0002, 2.0052 ± 0.0002, and 2.0075 ± 0.0002. These data are consistent with a radical formed in the deoxyribose sugar group as a result of hydrogen abstraction at the C5′ position.
Calculation of H/D Kinetic Isotope Effects for the Reactions of Trifluoromethyl Radicals with SiH4
Authors: Safarik I. , Berkley R. , Strausz O. P.
Published: February 2004

Primary and secondary kinetic isotope effects for the reactions of trifluoromethyl radicals with SiH4 and SiD4 have been calculated within the framework of transition-state theory using a complete nine-atom model for the activated complex. The effect of variation of the applied force field has been investigated. Comparison of the results with the experimentally measured values suggests the occurrence of quantum mechanical tunneling in the reactions.
Application of the Environmental Relaxation Model to the Temperature Dependence of the Viscosity
Authors: Tweer Herbert , Simmons Joseph H. , Macedo Pedro B.
Published: February 2004

An equation relating viscous flow processes to local microstructure is applied to the viscosity of nine materials belonging to different classes of glass formers. It is seen that the model proposes the correct general behavior for the viscosity and the associated activation energy distributions. The model further explains this behavior in terms of a temperature-dependent ordering process in the structure of the material occurring at low temperatures. Finally, a simultaneous fit of the viscosity and the conductivity of a molten salt yields parameters whose relationships are physically meaningful in terms of the viscous relaxation and conduction relaxation processes.
Neutron Diffraction Study of the Structure and Thermal Motion of Phosphonium Bromide
Authors: Schroeder L. W. , Rush J. J.
Published: February 2004

The crystal structure of PH4Br has been determined by a single-crystal neutron diffraction study. The tetragonal structure is similar to that determined previously for PH4I with the P–H bonds of the phosphonium ions directed at the four next-nearest-neighbor halide ions. The corresponding P–H and H···Br distances are 1.414 and 2.65 Å, respectively, with a P–H···Br angle of 172°. The orientation of the PH4+ ions (90° away from the orientation of NH4+ in the analogous phase III (NH4Br) suggests that hydrogen bonding plays a minor role in determining the crystal structure. A “rigid-body” analysis of the motion of the PH4+ ion was performed using the anisotropic thermal parameters of the phosphonium and hydrogen atoms derived from the PH4Br and PH4I diffraction data. The resulting mean-square amplitudes of translational and torsional motion of the PH4+ ion lead to frequencies which are in good agreement with spectroscopic observations.
Vibrational Relaxation of CO in Nonequilibrium Nozzle Flow, and the Effect of Hydrogen Atoms on CO Relaxation
Authors: von Rosenberg C. W. , Taylor R. L. , Teare J. D.
Published: February 2004

The vibrational relaxation of carbon monoxide was studied under conditions of rapid nonequilibrium expansion by using a shock tunnel to generate a nozzle flow with stagnation temperatures and pressures of 2000–4500°K and 5–15 atm., respectively. The vibrational temperature of the CO in the supersonic region of the nozzle was obtained from measurements of the first overtone emission at 2.3 μ by using a calibrated infrared detection system. From these data it was determined that the relaxation time of the CO inferred from the expansion experiment is, at most, 5 times smaller than the relaxation time measured behind incident shock waves. This factor of 5 is in sharp disagreement with previously published measurements in CO and N2, which quote factors from 70 to 1000, implying anomalously fast de-excitation of vibration in expanding flows, but is in agreement with other subsequently obtained measurements. Impurities were found to be more important in this type of experiment than in measurements of relaxation time behind incident shock waves mainly because of additional ways of their getting into the flow. Hydrogen atoms were found to have a probability per collision for the de-excitation of CO of P10 = 0.01 to 0.3 for T = 1400–2800°K. It is not certain whether the observed factor of 5 for pure CO is due to residual impurity effects or due to effects of anharmonicity as discussed in recent theories.
Magnetic Properties of Tb–Ho Single Crystal Alloys. III. Neutron Diffraction Studies of Ho Rich Alloys
Authors: Spedding F. H. , Ito Y. , Jordan R. G. , Croat J.
Published: February 2004

Neutron diffraction studies on several polycrystal and single crystal samples of Ho rich Tb–Ho alloys are reported. Polycrystalline samples containing 90%, 92%, 94%, 96%, and 98% Ho, as well as pure Ho, were studied at room temperature and at 8°K as a preliminary investigation for subsequent single crystal work. Three single crystal samples containing 93%, 95%, and 98% Ho were studied in detail from room temperature to 4.2°K. Both the Curie and Néel temperatures of the single crystal alloys were found to decrease almost linearly as the Ho concentration was increased. Both the 93% and 95% Ho alloys were found to have ordered phases similar to that of the 90% Ho alloy, with the exception that fifth and seventh harmonics caused by the distortion of the simple helical arrangement were observed for 95% Ho between 40°K and the Curie temperature at about 15°K. We find that the magnetic structure of the 98% Ho alloy corresponds to a magnetic structure on the borderline between that of pure Ho and that of 90% Ho. It shows all the characteristic features observed for pure Ho with the important exception that it does not transform to the conical spiral structure. Rather, the moments are still confined to the basal plane, most of them in the distorted helical arrangement bunched around the easy b direction, with some 4.4% of them collapsed into ferromagnetic ordering along the b direction.
Study of Impurity–Host Coupling in Shpolskii Matrices
Authors: Richards John L. , Rice Stuart A.
Published: February 2004

The nature and strength of the impurity–matrix coupling in Shpolskii matrices (frozen normal alkane matrices) have been determined from a study of the absorption linewidth, position, and intensity of several of the vibronic bands of anthracene, naphthalene, coronene, and 1, 12 benzperylene dissolved in their appropriate n-alkane solvents. At 4°K the half-intensity linewidths of the first electronic absorption bands are small (2–6 cm−1). In coronene the second absorption band is also narrow at 4°K (4 cm−1). Comparison with a theory originally developed for inorganic impurity–matrix systems yields values for the impurity lattice coupling parameters which are of the same order of magnitude as those found for f-electron excitations in rare-earth impurity–matrix systems. Because Shpolskii matrices are weakly interacting host crystals for aromatic solutes, it is possible to study the upper excited states of such solutes as if they were a “dilute cold gas.” The implication of this observation for the study of radiationless processes is indicated.
Perturbation Theory for a High-Temperature Triangle-Well Fluid
Authors: Farrar W. C. , De Rocco Andrew G.
Published: February 2004

Using the PY approximation to the radial distribution function for hard spheres, the first temperature correction to the fourth virial is obtained for a triangle-well perturbing potential. The results are compared with those obtained for a square well and a LJ (12–6) with a hard-sphere cutoff. The TW is shown to be in somewhat closer agreement with the LJ (12–6) than is the SW and for the same value of the cutoff (n = 2) that characterizes similar agreement for the lower virial coefficients.
Many-Body Aspects of Physical Adsorption
Authors: MacRury T. B. , Linder B.
Published: February 2004

A theory is presented for determining the effect of many-body interactions on the dispersion energy of a pair of gas molecules adsorbed on a crystalline solid. The formalism is based on a reaction field technique and includes potential nonadditivity to fourth order. Model calculations are carried out for the change in the interaction energy between a pair of Ne atoms, a pair of Ar atoms, and a pair of Kr atoms adsorbed on solid Xe by summing over the Xe lattice. The results are analyzed and compared with calculations based on a model which treats the solid as a continuous dielectric.
Optical Model Analysis of Nonreactive Collisions of Reactive Molecules: Scattering of K, Rb, and Cs from CCl4, CH3I, and SnCl4
Authors: Harris R. M. , Wilson J. F.
Published: February 2004

Crossed beam studies of nonreactive scattering of K, Rb, and Cs atoms from CCl4, CH3I, and SnCl4 have been carried out and the differential cross sections compared with calculations based on a phenomenological optical model analysis. The models employed make use of a parameterized “reference” potential which is intended both to represent a multipole expansion of the potential surface of the reactants for internuclear distances greater than the radius of chemical interaction, and to provide a systematic means of calculating the real parts of the optical phase shifts. A new semiclassical method for calculating nonreactive differential cross sections for an isotropic central potential (reference) and a parameterized probability of reaction (opacity) function, P(β), is presented and applied to the scattering of M+CCl4. It is found that the observed cross sections are consistent with a Lennard-Jones reference potential and a P(β) which is a rounded-off step function. A better description of the reactivity for these systems was obtained by expressing the opacity function in terms of y, the reduced distance of closest approach, instead of the impact parameter β. The velocity dependence of the opacity function was virtually removed upon making this transformation, and the reactivity for a given alkali atom was found to resemble a diffuse “black sphere” of radius yc, the opacity becoming less diffuse in the order Cs<Rb<K. The optical model has been extended to include an anisotropic term in the reference potential for analysis of the nonreactive scattering of M+CH3I. The magnitude of the anisotropic term was found to be much larger than that predicted from long-range dispersion forces alone. It is shown that the large anisotropy can account for the sudden decrease in the wide angle nonreactive scattering, which was previously interpreted as a reaction threshold angle. Probability of reaction functions were derived from the data, and the results were consistent with the steric effect found in experiments which employ oriented CH3I molecules. The cross sections for M+SnCl4 are interpreted on the basis of orbiting from an “electron jump” potential, which is the adiabatic potential resulting from the crossing of covalent (M+SnCl4) and ionic (M++SnCl4−) curves. Parameters for the potential are extracted from the data and used to estimate the electron affinity of the SnCl4 molecule. The value obtained, 2.1 ± 0.2, is in fair agreement with a recent estimate from direct measurement of the threshold for ion-pair formation.
Theory of Molecular Polaritons. Application to the Reflection Spectra of Anthracene, 1,5-Bis(dimethylamino)pentamethinium Perchlorate, and Some Other Cationic Dye Crystals
Authors: Philpott Michael R.
Published: February 2004

The reflection spectra of anthracene in the 3800 Å region and 1,5-bis(dimethylamino)pentamethinium perchlorate (BDP) in the 4090 Å region are calculated using molecular polariton theory. In the crystal the anthracene transition, oscillator strength f = 0.1, involves weak to intermediate vibronic coupling of molecular exciton states, and the model calculations easily reproduce the main features of the observed reflection spectrum. In contrast, the intense transition (f = 3.31) of the dye BDP involves strong vibronic coupling of molecular excitons, and polariton theory with phenomenological damping constants does not adequately reproduce the “vibrational” structure observed in the reflection spectra. Theory and experiment are reconciled by considering the coupling among and distribution of two-exciton states in which vibronic and vibrational excitations occupy different lattice sites.
Metastable a 3Π 13CO: Molecular-Beam Electric-Resonance Measurements of the Fine Structure, Hyperfine Structure, and Dipole Moment
Authors: Gammon R. H. , Stern R. C. , Lesk M. E. , Wicke B. G. , Klemperer W.
Published: February 2004

The radio-frequency spectrum of metastable a 3Π 13CO has been measured in molecular-beam electric resonance in the range 0–2000 MHz. Electric-dipole transitions with ΔJ = 0 and ΔF = 0, ± 1 have been observed in states | υ, Ω, J, F〉 = | 0–3, 1–2, 1–7, J ± 12〉 at zero field. The set of transitions in each vibrational state has been analyzed to give three parameters describing the lowest-order magnetic hyperfine interactions of the 13C nuclear spin (I = 12) with the spin (S) and orbital (L) angular momenta of the two unpaired electrons in the 5σ2π open-shell configuration. The vibrational dependence of the measured hyperfine parameters is fitted to a polynomial in (υ + 12)n to give: OriginParameterValue at Re(a 3π) (in MHz)I·SFermi contactK=1935.1 ± 0.5I·Sspin–spin dipoleDδ=106.5 ± 0.1D=7.9 ± 0.1I·Lspin–orbitalG=162.5 ± 0.1 Restricted Hartree–Fock calculations of these hyperfine terms are in good agreement with the measured values. The Stark effect has been measured in states | υ, Ω, J, F〉 = | 0–3, 2, 2–3, J + 12〉 of a 3Π 13CO to give dipole moments which display a slight nonvibrational isotopic shift (1 in 104) from the moments measured in the corresponding states | υ, Ω, J〉 of a 3Π 12CO.
Molecular-Beam Electric-Resonance Spectroscopy of the a 3Π (υ = 4)−a′ 3Σ+ (υ′ = 0) Perturbation in CO
Authors: Gammon R. H. , Stern R. C. , Klemperer W.
Published: February 2004

The heterogeneous perturbation of the a 3Π (υ = 4) state of CO by the nearly degenerate a′ 3Σ+ (υ′ = 0) state is observed in the rf electric–dipole spectrum of the metastable a 3Π (υ = 4) state. Perturbed lambda doublings and Stark effects in states | υ, Ω, J〉 = | 4, 2, 2–6〉 have been measured in molecular-beam electric resonance from 7–400 MHz. These measurements are combined with existing optical data to obtain the off-diagonal matrix elements of the fine structure which describe the a–a′ interaction, 〈a 3Π ‖ AL+ / 2 ‖ a′ 3Σ+〉 = − 18.1 ± 0.3 cm−1, 〈a 3Π ‖ BL+ ‖ a′ 3Σ+〉 = 0.16 ± 0.01 cm−1, and the diagonal and off-diagonal components of the dipole moment, 〈a 3Π ‖ μ ‖ a 3Π〉 = 1.3791 ± 0.0003 D, 〈a 3Π ‖ μ ‖ a′ 3Σ+〉 = 0.62 ± 0.02 D. This last quantity is identically the electronic transition moment of the (a′ 3Σ+−a 3Π) Asundi system.
ESR Studies of Covalent Copper Complexes with a Rhombic Arrangement
Authors: Buluggiu E. , Dascola G. , Giori D. C. , Vera A.
Published: February 2004

A method of calculation of bond parameters is proposed for magnetic molecular orbitals which describe the 3d9 configuration in the case of complexes with a rhombic surrounding (D2h symmetry), when the experimental spin Hamiltonian is known. This treatment contains as a particular case that of Kivelson et al. for square planar structures and allows us to evaluate both the anisotropic presence of unpaired spin at the various ligands, and the mixing of the d3z2−r2 orbital in the ground state which is essentially dx2−y2. Applications of this treatment in calculating the bond parameters in the CuCl2·2H2O and CuF2·2H2O compounds allow a comparison between the covalent characters of the Cu–Cl and Cu–F bonds in a similar surrounding. The results show that there is a relevant spin density at the halide ions in both compounds and that, in CuCl2·2H2O, the anisotropy of covalence in the principal plane of coordination is strong. The reliability of the proposed criteria is considered by a comparison between the covalence values obtained following our method and those obtained directly from the extrahyperfine structure in the case of a square planar copper complex.
Molecular Collisions. XIV. First-Order Approximation of the Generalized Phase Shift Treatment of Rotational Excitation: Atom–Rigid Rotor
Authors: Pattengill M. D. , Curtiss C. F. , Bernstein R. B.
Published: February 2004

The generalized phase shift approach to the rotational excitation problem, introduced in Paper XII of this series, is applied to the atom–rigid rotor case in the lowest (first-order) approximation. The treatment involves the computation of generalized action integrals over curved trajectories. Numerical results are presented to illustrate the dependence of the transition probabilities on the usual physical parameters, as well as a new parameter, ζ, which is proportional to the ratio of the moment of inertia of the van der Waals' atom–diatom system to that of the diatomic rotor (and thus to the ratio of the collision time to the diatom rotation time). In the limit ζ → 0, the development reduces to the sudden approximation. In the large impact parameter limit (straight-line trajectories), the deviation from the sudden approximation is described by “resonance functions” identical to those obtained implicitly by Van Kranendonk. The numerical results are presented in a manner which illustrates the deviation from each of these two limits.