bluuebunny/crossref_metadata_2025 huggingface dataset:
Dimers and Clusters in Free Jets of Argon and Nitric Oxide
Authors: Golomb D. , Good R. E. , Brown R. F.
Published: February 2004

Molecular cluster abundances of argon and nitric oxide have been measured with a mass spectrometer in free jets with reservoir pressures p0 from 10–104 torr and nozzle diameters d of 0.034 and 0.117 cm, using a phase-sensitive detection system to eliminate background effects. For a given nozzle diameter, the dimer and larger cluster signals increase with rising reservoir pressure until a peak is reached. The position of the peak scales with d and occurs at a constant factor p0d of 100 ± 10 torr·cm for argon and 78±4 torr·cm for nitric oxide. It is proposed that the peaks of dimer and cluster abundances indicate condensation in the expanding jet. The maximum number of clusters formed depends on nozzle diameter and reservoir temperature. In argon the dimer mole fraction exceeded 0.5, in nitric oxide the maximum detected mole fraction was 0.03. A three-body dimer formation mechanism is invoked to compare the observed and estimated dimer abundances in an expanding jet.
Anisotropic Electron Spin Resonance Spectrum of PF2 in Low-Temperature Matrices
Authors: Wei Michael S. , Current Jerry H. , Gendell Julien
Published: February 2004

The anisotropic electron spin resonance spectrum of the PF2 radical has been observed. P2F2 was thermally decomposed by passing the gas over a hot wire. The radicals produced were trapped in an argon matrix on a flat sapphire rod held at 20°K. The same radicals were formed by photolysis of PF2H in an argon matrix. In contrast to N2F4, PF2 radicals were not detected unless the P2F4 was heated above 200°C. The observed 12-line ESR spectrum is interpreted as being due to randomly oriented nonrotating radicals with axially symmetric g and hyperfine tensors. Based on computer-simulated spectra, the following assignment has been made: g‖ = 2.0011, g⊥ = 1.9922; C‖ = (P) = 307 G, C⊥(P) = − 83.0 G; C‖(F) = 127 G, C⊥(F) = 33.5 G. The same radical was also trapped in different matrices. The nature of the trapping sites and the effect of environment on the radicals is discussed. Comparison with data available for NF2 indicates that the unpaired electron in PF2 is localized on the central atom to a greater extent than it is in NF2. Extended Hückel calculations also give this result.
Laser-Induced Fluorescence of BaO
Authors: Sakurai Katsumi , Johnson S. E. , Broida H. P.
Published: February 2004

Fluorescence spectra of the A 1Σ − X 1Σ system of BaO excited by seven visible Ar ion laser lines have been observed over a wavelength region from the exciting lines to beyond 1000 nm. The strongest fluorescence was observed from υ′ = 8, J′ = 49 excited by 488.0 nm and υ′ = 7, J′ = 3 and 7 excited by 496.5 nm. The rotational and vibrational assignments of the various excitation transitions have been made, and rotational and vibrational constants for the lower electronic state were obtained. A rotational perturbation in υ′ = 7 of the upper electronic state was found. Studies have been made, from 0.4 to 40 torr, of the collisional energy transfer to other rotational and vibrational levels of the A 1Σ state after optical pumping by laser lines. The lifetime of the A 1Σ state of BaO was found to be 12 ± 3 × 10−6 sec. The BaO molecules were produced by gas-phase chemical reactions between O2 and Ba vapor in an inert gas at room temperature. A weak chemiluminescence of the A 1Σ − X 1Σ system of BaO was observed.
Some Propensity Rules in Collision-Induced Rotational Quantum Jumps
Authors: Ottinger Ch. , Velasco R. , Zare R. N.
Published: February 2004

When a mixture of lithium vapor and argon is irradiated with the light from an argon ion laser and the resulting fluorescence of the Li2 B 1Πu − X 1Σg+ band system is examined under high resolution, a pattern of collision-induced satellite lines is observed to accompany the parent resonance fluorescence series. Under conditions of low pressure these satellite lines originate from single inelastic events which alter the rotational state of the excited Li2 molecule. The relative intensities of the satellite lines are found to be markedly different depending on whether the collision-induced transition originates from the upper or lower component of the Lgr; doublet of the Π state, referred to as c or d, respectively. An increase in J(+ ΔJ jump) is favored over a decrease (− ΔJ) for d → c jumps whereas − ΔJ is favored over + ΔJ for c → d jumps. On the other hand ± ΔJ changes that preserve the character of the Λ component, i.e., c → c and d → d, occur with nearly equal probability for the same value of ΔJ. This behavior has been observed for the satellite lines corresponding to ΔJ = ± 1, ± 2, and in some cases ± 3 for (υ′, J′, c, or d) levels (2, 31, c), (3, 30, c), (9, 38, c), (4, 24, d), and (7, 61, d) of 7Li2 and (0, 45, d) of 6Li 7Li. In 7Li2 only collisional transitions between symmetric or between antisymmetric levels are allowed. For 6Li 7Li, which does not have this symmetry, more satellite lines are observed. However, these additional lines are significantly weaker since the 6Li 7Li molecule is nearly homonuclear. A simple classical model is suggested which may help to explain the different rotational quantum jump propensities for the two Λ components.
2491-Å Absorption System of NO2 and a Double-Minimum Potential
Authors: Coon J. B. , Cesani F. A. , Huberman F. P.
Published: February 2004

The 2491-Å absorption system of N16O2 and the corresponding system of N18O2 have been photographed at temperatures up to 600°C. For each molecular species measurements yield the ground-state frequencies ν1″, ν2″, 2ν1″,and ν1″ + ν2″ as well as the excited-state frequencies ν1′, ν2′ and 2ν3′. A large isotope shift observed for the (0–0) band is found to be consistent with the assignment 2ν3′ = 713 cm−1 even though this frequency is quite small compared to the frequency ν1′ = 1156 cm−1. Two facts which demand explanation are the isotope shift of the frequency ,2ν3′, and the relative intensity of the cold band involving 2ν3′. These facts cannot be explained in terms of harmonic potential in the antisymmetrical coordinate Q3′, but can be explained in terms of a double-minimum potential in this coordinate. The barrier of this potential is about 722 cm−1 and the inversion doubling is near 103 cm−1. At vibrational equilibrium the calculated N–O bond lengths are 1.426 and 1.202 Å.
Electronic Spectra of Cesium Fluoride Complexes of Pentavalent Neptunium
Authors: Varga L. P. , Asprey L. B. , Keenan T. K. , Penneman R. A.
Published: February 2004

The absorption spectra of magenta-colored CsNpF6 both as a mull of the crystalline solid and as a solution in CsF·2HF were obtained under various conditions. The room-temperature spectra were unique to the electronic energy levels of the seven Russell–Saunders states for the 5f2 configuration, split by spin–orbit coupling into 13 free-ion levels; this confirms the chemical evidence for the presence of pentavalent neptunium. At liquid-nitrogen temperatures the spectra of CsNpF6 mulls were interpreted in terms of the free-ion f–f transitions of Np5+ split by an Oh crystal field. Term assignments to the following experimental energy levels obtained at room temperature were made on the basis of the observed Stark splitting in the low-temperature spectra, and agreement with calculated energy levels (in cm−1): F23 = 4337, 3H5 = 8425, 3F3 = 8797, 3F4 = 9701, 3H6 = 13 738, 3P0 = 16 129, 1D2 = 16 736, 1G4 = 18 265, 3P1 = 19 531, 1I6 = 20 619, 3P2 = 26 667. All levels above the H43 ground state were observed except S01. A least-squares fit of these experimental energy levels was made to the Racah Coulomb interaction parameters, E1 = 2807 cm−1, E2 = 19.98 cm−1, E3 = 284.1 cm−1; the spin–orbit coupling parameter ζ = 2316 cm−1; and the configuration-interaction parameters, α = 2.7 cm−1 and β = 52.9 cm−1. The position of the 5f2 levels of Np5+ on the intermediate coupling diagram compared to the f2 levels of the isoelectronic series Pr3+, Nd4+, Th2+, U4+, and Pu6+ (in PuF6) was intermediate between U4+ and Pu6+ as expected.
Proton Magnetic Resonance of Ammonia at Low Temperatures
Authors: O'Reilly D. E. , Peterson E. M. , Lammert S. R.
Published: February 2004

Proton relaxation times (T1, T2, T1ρ) were measured for liquid and solid ammonia from 50 to 280°K. Second moments (M2) were determined from the melting point (195°K) to 10°K. In the liquid T1 ≠ T2 due to spin–spin coupling of the proton and nitrogen-14. The spin–spin interaction is modulated by chemical exchange above 220°K which has an activation energy of 1.9 kcal mole−1. T1 decreases discontinuously by an order of magnitude at the melting point with decrease in temperature and reaches a minimum at 119°K. The activation energy for the threefold axis reorientation of the NH3 molecule is 2.41 kcal mole−1 and the intramolecular H–H distance is 1.63 Å. T1ρ decreases with increase in temperature from about 160°K to the melting point. This corresponds to self-diffusion in the solid with an activation energy of 4.94 kcal mole−1. M2 increases from 14 G2 above 90°K to 20 G2 below 70°K but does not attain the calculated rigid lattice value of 48 G2. This effect appears to be due to quantum-mechanical tunneling at low temperatures with a frequency of about 60 kHz. The self-diffusion observed in the solid is interpreted with reaction rate theory models. It is necessary to introduce a orientational transmission factor that is equal to 5 × 10−3 in order to account for the magnitude of the observed self-diffusion coefficients and jump times.
Comparison of Lennard-Jones and Exponential-Six Pair Potentials for Solid Argon at Low Pressure
Authors: Hoover W. G. , Holt A. C. , Shortle D. R. , Gray S. G.
Published: February 2004

Monte Carlo calculations of thermodynamic properties for solid argon are carried out using both the Lennard-Jones and the exponential-six pair potentials. When quantum corrections are taken into account the calculated energies and pressures derived from the Lennard-Jones potential agree better with experiment. Neither pair potential successfully reproduces the experimental elastic constants.
Aerodynamic Separation Effect on Gas and Isotope Mixtures Induced by Invasion of the Free Jet Shock Wave Structure
Authors: Campargue Roger
Published: February 2004

The shock wave system of the underexpanded free jet, in a region where the pressure is in the range of 10−2 up to 1 torr, is partly invaded by background molecules, these latter being pumped and carried by the supersonic flow. When a gas mixture is introduced into the nozzle chamber and outside the shock barrel, this aspiration acts very selectively on the light molecules, and a mixture enriched in lighter species is attainable by skimming the free jet. This new aerodynamic separation effect, which is applicable to isotopic mixtures, is very strong in comparison to the efficiency of an elementary gaseous diffusion membrane.
Rotational Relaxation in Fluids
Authors: Kivelson D. , Kivelson M. G. , Oppenheim I.
Published: February 2004

In this paper a number of expressions for angular momentum and reorientation correlation times are obtained. The inverse of the angular momentum correlation time is related to a sum of two terms, one of which involves the shear viscosity of the medium and the other of which describes the precessional relaxation of the molecule. The derivation is based on the similarity of the time dependences of the torque and the force exerted on the molecule of interest. The reorientation correlation time is related to the angular momentum relaxation time in the diffusion and the near-diffusion limits. The expressions obtained here have been confirmed by a number of ESR experiments.
Photolysis of Ethane at 11.6–11.8 eV
Authors: Lias S. G. , Collin G. J. , Rebbert R. E. , Ausloos P.
Published: February 2004

The photolysis of ethane, carried out with an argon resonance lamp, has been reinvestigated with the related purposes of (1) measuring quantum yields of all fragments formed in the dissociation of excited ethane and (2) associating these fragments with the primary processes occurring in the photolysis of ethane. These and their relative abundances are C2H6*→C2H6+, 5% →CH4+CH2, 16% →C2H5+H, 41% →C2H4+H2, 26% →CH3+CH3, 15%. These results are compared with conclusions reached in earlier studies on the photolysis of ethane with xenon and krypton lamps in order to determine the effect of energy on the relative probabilities of the primary processes. It is found that direct bond scission increases in importance with increasing energy, while processes involving rearrangement decrease in importance. The radical and molecular fragments formed in the dissociation of excited ethane were determined by (a) analyzing the products formed in C2H6–C2D6–NO (1:1:0.1) mixtures and (b) C2D6in the presence of H2S, which scavenges free radicals to form isotopically unique hydrocarbon products, and (c) C2H6 in the presence of C3D6, which scavenges H atoms to form propyl radicals, which in turn react with radicals in the system to form characteristic products. Such experiments, as well as quantum yield determinations, were also carried out at the krypton and xenon lines.
Optical Emission from O(1D) and O2(b 1Σg) in Ultraviolet Photolysis of O2 and CO2
Authors: Noxon J. F.
Published: February 2004

The presence of O(1D) has been detected via 6300 Å emission in ultraviolet photolysis of O2 and CO2. Quenching rates for O(1D) and O2(1Σg) have been measured for O2, N2, CO2, and CO; we also find that quenching of O(1D) by O2 yields O2(1Σg) with nearly unit probability. The quenching rates compared well with those deduced from day airglow emission from the upper atmosphere; however we find a much smaller quenching rate by CO2 on O(1D) than have earlier workers using less direct methods. Photolysis of O2–CO mixtures leads to optical emission which exhibits a pronounced periodic variation in time. The quenching coefficients for O2, N2, CO2, and CO, in order, are as follows (cm3/sec): for O(1D), k1 = 6 × 10−11, k2 = 9 × 10−11, k3 = 3 × 10−12, k4 <5 × 10−11; for O2(1Σ)k5 = 1.5 × 10−16, k6 = 2 × 10−15, k7 = 3 × 10−13, k8 = 3 × 10−15.
Temperature Dependences of the Rate Coefficients for the Reactions of Ar+ with O2, H2, and D2
Authors: Adams N. G. , Bohme D. K. , Dunkin D. B. , Fehsenfeld F. C.
Published: February 2004

A series of measurements have been made using the flowing afterglow technique to investigate the temperature dependence of the rate coefficients for the reactions of Ar+ with O2, H2, and D2 in the temperature range 80–560°K. The rate coefficient for the reaction of Ar+ with O2 has been found to decrease with increasing temperature approximately as T−0.5. In contrast, the rate coefficients for the reactions of Ar+ with H2 and D2 increased with increasing temperature, and the rate coefficients for the reactions ArH+ + H2 and ArD+ + D2 were independent of temperature within experimental error. The rate coefficient for the reaction of Ar+ with N2 was measured at 280°K and found to be dependent on the Ar number density.
Carrier Lifetimes in γ-Irradiated Anthracene
Authors: Ringel H. , Whitten W. B. , Damask A. C.
Published: February 2004

The effect of 60Co gamma rays on the lifetimes of photoinjected electrons and holes in anthracene has been studied. Reciprocal lifetimes of both carriers vary linearly with dose. Steady-state space-charge-limited current measurements gave a production rate for deep electron traps of 1.4 × 109 cm−3·R−1. The variation of lifetime with dose is interpreted in terms of radiation-produced traps with trapping cross sections comparable to the geometric cross section of a unit cell.
Hydrogen–Deuterium Self-Exchange in Hydrogen Sulfide and Hydrogen Selenide as Studied with a Pulsed-Molecular-Beam Quadrupole Mass Filter
Authors: Pyper J. W. , Newbury R. S.
Published: February 2004

The equilibrium constants for hydrogen–deuterium self-exchange in hydrogen sulfide and hydrogen selenide have been studied over a wide range of deuterium atom percent using a pulsed-molecular-beam quadrupole mass filter. KHDS was found to be 3.88 ± 0.03 at 24.0 ± 0.4°C and KHDSe was found to be 3.92 ± 0.04 at 22 ± 1°C. The experimental results agree with calculations from spectroscopic data to within 1%. It is shown that equilibrium constants for self-exchange reactions in systems where two hydrogenic species are exchanged tend toward the geometric mean value of K = 4 in the series H2O:H2S:H2Se as expected from theory.
Effusion from Knudsen Triple Cells
Authors: Bidwell Lawrence R.
Published: February 2004

A quantitative theory for vapor effusion from Knudsen triple cells has been developed. These cells, when used in conjunction with a mass spectrometer, permit a direct determination of the thermodynamic activity of a binary alloy component. In conventional Knudsen effusion studies, the vapor pressure of an element in an alloy and in the pure state is determined in separate experiments, and the ratio is used to compute the activity. Because of the exponential relationship between vapor pressure and temperature, even small errors in temperature reproducibility result in large errors in the calculated activities. The Knudsen triple cell avoids these errors but is subject to other limitations that are discussed.
Electron Spin Resonance Studies of Irradiated Single Crystals of Dihydrothymine
Authors: Henriksen Thormod , Snipes Wallace
Published: February 2004

Both the 5-thymyl radical and the 6-thymyl radical are formed when dihydrothymine is irradiated at room temperature. In this paper the 6-thymyl radical is analyzed in detail by use of electron spin resonance (ESR) spectroscopy. Principal values for the spectroscopic splitting tensor are gu = 2.0039, gυ = 2.0031, and gw = 2.0022. Hyperfine coupling to the β proton is nearly isotropic with Aβ = 44.0 G. The α-proton hyperfine tensor has principal values, in gauss, of Axα = 7.8, Ayα = 26.9, Azα = 17.5. Comparisons between the principal axes for the ESR parameters and the known crystal structure of dihydrothymine indicate that radical formation is accompanied by a conformational change in the pyrimidine ring. This change results in a radical structure which is more nearly planar than the original puckered dihydrothymine molecule. Irradiation and observation at 77°K revealed that both the 5-thymyl radical and the 6-thymyl radical are formed, but the relative quantities of the two radicals are different than at room temperature.
Stress Relaxation in Solutions of Linear Macromolecules
Authors: Bird R. Byron , Warner Harold R. , Ramakka William R.
Published: February 2004

The rigid dumbbell model has been used to derive expressions for the relaxation of shear and normal stresses after the cessation of steady shearing flow. It is found that the shear stresses relax more rapidly than the normal stresses, and that all stresses relax more rapidly as the velocity gradient during the prior steady state shearing flow increases; this behavior is in qualitative agreement with experimental data. The results further show that the integral under the shear-stress relaxation curve is simply related to the normal stress in steady flow. The elastic dumbbell model, with a Gaussian spring, gives results inconsistent with experiment.
Interaction Coordinates and Compliance Constants
Authors: Jones Llewellyn H. , Ryan Robert R.
Published: February 2004

It is shown that interaction coordinates are closely related to compliance constants. Also it is emphasized, using a vibrational analysis of H2O as an example, that compliance constants are invariant with the force field and thus are more unique quantities than are force constants.
Theoretical Study of the Barriers to Internal Rotation in Formic Acid
Authors: Schwartz Maurice E. , Hayes Edward F. , Rothenberg Stephen
Published: February 2004

The nonempirical self-consistent-field molecular-orbital method with a basis set of groups of accurate Gaussian atomic orbitals has been used to study formic acid, HCOOH, for three different geometries. The conformer with the hydroxyl hydrogen cis to the carbonyl oxygen is correctly computed to be the most stable. This geometry is 13.0 kcal lower in energy than the geometry with the hydroxyl hydrogen at a 90° dihedral angle with the carbonyl oxygen (experimental estimate: 13.4 kcal) and 8.1 kcal lower than the trans form (experimental estimate: ≥ 4 kcal). The population analysis suggests a screening of the carbonyl oxygen in the high nuclear repulsion cis form and a partial breaking of the hydroxyl oxygen–carbon bond from cis to 90°. The electronic contribution to the calculated dipole moment shows shifts of electronic charge toward the carbonyl end of the molecule in cis and trans forms compared to the 90° form. Molecular properties related to the nuclear–nuclear and nuclear–electron potentials at the various nuclei exhibit increased attraction of electronic charge for a given nucleus when that nucleus is in an energetically unfavorable nuclear potential field, illustrating nuclear screening as an important feature of the barrier.
Further Studies on Temperature Dependences of Isotope Effects
Authors: Spindel W. , Stern Marvin J. , Monse E. U.
Published: February 2004

It is shown that, although the temperature behavior calculated in the harmonic approximation for a specific isotope-exchange reaction may be extremely sensitive to the force fields used in the computations, small force-field changes do not affect significantly the over-all prevalence of temperature-dependence “anomalies.” In a series of calculations for a large number of 13C-, 18O-, and D-isotope-exchange equilibria involving organic and inorganic molecules, such “anomalies” are found in 50 of the 171 13C exchanges considered, in 84 of the 153 18O exchanges considered, and in 40 of the 120 D exchanges considered. When the present results are combined with previous results for 15N- and 18O-exchange reactions involving simple inorganic molecules, “anomalies” appear in about 40% of the almost 700 reactions investigated. It is concluded that isotope-effect temperature-dependence “anomalies” are not due to unusual or fortuitous combinations of force constants, but represent a more general phenomenon. Further, the phenomenon is not restricted to particular structural features in molecules or to isotopes of particular elements.
Dissociation of the Hydrogen Molecule–Ion from the Viewpoint of the Integral Hellmann–Feynman Formula
Authors: Marron Michael T. , Parr Robert G.
Published: February 2004

The dissociation energy of the hydrogen molecule–ion is computed and analyzed by means of the integral Hellmann–Feynman theorem. The molecule is considered to dissociate either unsymmetrically by the removal of one of the nuclei to infinity or symmetrically by the simultaneous removal of both nuclei to infinity. The energy change is computed for each path and compared with the difference of the energy expectation values for the initial and final states. The Hellmann–Feynman results are in general different for the two paths, while the differences of expectation values are not. The final separated-atom state is represented by the exact wavefunction. The initial state is represented by a variety of wavefunctions including variational functions in both AO bases and elliptic MO bases, wavefunctions with correct cusp behavior forced, wavefunctions which approximate correct long-range behavior, and wavefunctions formed from a linear combination of initial-state functions and final-state functions. A dissociation process wherein the nuclear charge increases upon dissociation is also examined. The integral Hellmann–Feynman method produces a 0  0 indeterminacy for symmetric dissociation, which is resolved by a limiting procedure. The integral Hellmann–Feynman approach involves the construct of transition density, which contains information about reorganization of electronic distribution from the initial to the final state, and which permits the dissociation energy to be expressed as the sum of the nuclear–nuclear repulsion energy and the classical electrostatic attraction energy of the nuclei for the transition density. Contour plots of the transition densities and plots of the transition densities along the internuclear axis are given.
Investigation of S → T and S → S Transitions by Phosphorescence Excitation Spectroscopy VII. 1-Indanone and Other Aromatic Ketones
Authors: Case W. Alan , Kearns David R.
Published: February 2004

A detailed examination of the phosphorescence excitation spectra of three aromatic ketones, acetophenone, p-bromoacetophenone and 1-indanone, has been carried out at both 77 and 4°K. The studies of 1-indanone demonstrate the following: (1) The 0–0 band of the S0 → S(n, π*) transition is allowed and polarized perpendicular to the plane of the molecule, indicating substantial delocalization of the oxygen long-pair orbital into the aromatic ring system. (2) Most of the intensity (80%–90%) in the S0 → S(n, π*) transition is vibronically induced. (3) A strong carbonyl progression appears to be absent in the S0 → S(n, π*) absorption spectrum, and this is attributed to mixing of the carbonyl stretching mode with other vibrational modes in the excited state. (4) The S0 → T(n, π*) transition has allowed character as a result of spin–orbit interaction between the T(n, π*) state and the La1(π, π*) state. (5) The intensification of the S0 → 1Lb transition in indanone relative to acetophenone is attributed to mixing of the Lb1 state with the La1 state induced by orthosubstitution. The introduction of La1 character into the Lb1 state is also responsible for the intensification of the S0 → T(n, π*) transition in indanone relative to acetophenone. (6) The 0–0 band of the S0 → T(π, π*) transition is allowed by spin–orbit coupling with the allowed, out-of-plane polarized component of the S0 → S(π, π*) transition. (7) Vibronic coupling between the T(π, π*) state and a nearby T(n, π*) state introduces significant in-plane polarized intensity into the S0 → T(π, π*) transition. Essentially similar results were obtained with acetophenone and p-bromoacetophenone, with the exception that the strong S0 → T(π, π*) transition in p-bromoacetophenone was found to be in-plane polarized parallel to the long-axis polarized transition to the La1(π, π*) state. Diffuseness observed in the 4°K single-crystal S0 → T spectra of each of the three compounds is attributed to vibronic interaction of the T(n, π*) with nearly degenerate vibronic levels associated with a lower-lying T(π, π*) state.
Vibrational Spectra and Structures of Ionic Liquids. IV. Isotopic Dilution of the Alkali Metal and Ammonium Nitrates
Authors: Devlin J. Paul , Li Paul C. , Pollard Gary
Published: February 2004

The isotopic isolation of the 14NO3− ion in molten Li15NO3 has been found to produce a 3-cm−1 increase in the ν2 (out-of-plane) frequency. This is interpreted as the result of the decoupling of 14NO3− ions in a perturbed lattice structure. The shift direction and magnitude resembles that observed upon isotopic decoupling of ions in solid LiNO3 and NaNO3. This comparison, plus the recently reported similarity between the far-infrared phonon spectrum of solid and molten NaNO3, is contrasted with other spectroscopic observations which suggest a substantial structural modification upon melting. For example, a 50% 15N lithium nitrate sample displayed an infrared é2 intensity anomaly which is thought to be characteristic of a stacked (orthorhombic) structure. It is suggested that most spectral features which seem to indicate substantial structural change upon melting may merely reflect the inevitable reduction in the symmetry of the cation field at the anion site as a consequence of cation vacancies. Several new Raman sightings are also reported, certain of which support the validity of earlier ATR infrared results in the ν3 range. The infrared and Raman spectra of NH4NO3 and ND4NO3 have also been determined guided by the assumption that ammonium nitrate would represent the limiting case of weak cation–anion interaction in ionic melts. However, the data indicate some distortion of both polyatomic ions, but, in contrast to the alkali metal nitrates, no evidence for anion–anion or cation–cation dynamical coupling has been detected.
Some Comments on the Variational Approach to the Theory of Simple Liquids
Authors: Henderson D. , Barker J. A.
Published: February 2004

The recently proposed variational approach to the perturbation theory of liquids is examined. It is found that although the approach yields good results in many applications, the use of the difference between the actual and reference intermolecular potentials as a perturbation can allow the perturbation to be infinite for some intermolecular separations. At best, this is unattractive and, at worst, will lead to poor results.
U-Band Transition Energies in Alkaline-Earth Fluorides
Authors: Singh R. S. , Galipeau David W. , Mitra S. S.
Published: February 2004

The singlet ground and first excited-state energy levels of U centers (substitutional H− ions) in alkaline-earth fluorides are calculated using a point-ion model. 1s2 → 1s2p transition energies for the center were found to be 6.82, 6.37, and 5.89 eV, respectively, in CaF2, SrF2, and BaF2. The oscillator strength for this transition is 1.8. The transition energies follow an Ivey-type relation with respect to the lattice constants, the exponent of which was found to be − 1.143. Effect of ion polarizations contributes less than 1% to the transition energy.
Polarized Infrared Spectra of TCNQ and TCNQ-d4 Single Crystals
Authors: Lunelli Bruno , Pecile Cesare
Published: February 2004

The infrared-active vibrations of the TCNQ molecular structure have been investigated by using the spectra of the powder and those of the (001) and (010) crystal planes in polarized radiation for both TCNQ and its fully deuterated analog. These measurements give most of the significant indications which can be drawn from infrared spectra for the localization and symmetry class identification of infrared active modes. As a result, a well-based assignment of infrared-active fundamentals, as well as some information on crystal field effects and on the optical behavior of this anisotropic crystal in the (010) plane, is given.
Absorptive Part of Charge Polarization Corrections for Electron Scattering in the Kiloelectron Volt Energy Range
Authors: Bonham R. A.
Published: February 2004

The calculation of the effect of the absorptive part of charge polarization on elastic electron scattering is investigated in the second Born approximation using closure in an approximate manner. Errors in a previous study are corrected, and the angular dependence of the polarization correction is found to be strongly peaked in the forward direction with a long tail at large s values which makes a significant contribution to the scattering. The effects of the polarization correction on the scattered intensity and on the phase of the scattered amplitude are discussed in view of experimental observations. Results for the case of elastic electron scattering from Xe are found to be in good agreement with experiment. Corrections to the diffraction measurement of chemical binding energies of molecules containing first-row elements appear to be negligible.
Second Virial Coefficients Using a Modified Lennard-Jones (6, n, γ) Potential
Authors: Koo Ronald Y. , Hsu H. W.
Published: February 2004

A four-parameter modified Lennard-Jones (6, n, γ) intermolecular potential function was used to calculate the reduced second virial coefficients of gases. Comparisons of the second virial coefficients calculated by the modified potential and the L-J (6, 12) potential with the experimental data points show that there is an improvement for using the modified potential for nitrogen, carbon dioxide, ethane, n-butane, ethylene, and benzene.
Luminescence Properties of [Cr(atp)6][Cr(CN)6]. Further Studies and Evidence against Cation/Anion Energy Transfer
Authors: Kirk A. D. , Schläfer H. L.
Published: February 2004

The temperature dependencies of Eg2[Cr(CN)6]3− emission intensity from K3[Cr(CN)6] and [Cr(atp)6][Cr(CN)6] and of T2g4[Cr(atp)6]3+ emission intensity from [Cr(atp)6][Cr(CN)6] and [Cr(atp)6] (ClO4)3 have been compared for excitation into the [Cr(atp)6]3+ and [Cr(CN)6]3− absorption regions. In addition the emission intensity differences have been measured. 77°K lifetime measurements on the Eg2 anion and T2g4 cation emissions from these compounds show the former to be 1000 times longer lived. Studies of the excitation spectra and of the emission spectrum of the double salt as a function of excitation wavelength are also described. The results show unequivocal evidence against major cation to anion energy transfer in this compound.
On the Solutions of the Rice–Allnatt Equation for Two Choices of the Fokker–Planck Operator
Authors: Baleiko Marc O. , Davis H. Ted
Published: February 2004

The Fokker–Planck operator that occurs naturally in the derivation of the Rice–Allnatt (RA) singlet kinetic equation is not the one actually used in the original solution of the RA equation. A simpler Fokker–Planck operator, being characterized by a constant friction coefficient, was used. Here, the transport coefficients predicted for each version of the Fokker–Planck operator are compared. The difference is not trivial, especially for such systems as dilute plasmas where long-range interactions tend to dominate over short-range interactions. Also, a new solution of the RA equation is presented—for both Fokker–Planck operators—in which the original isobaric assumption is eliminated. This analysis is simpler, yet more general, than the original analysis. Fortunately, the transport coefficients predicted from both solutions are in agreement. It is proved that the original RA Fokker–Planck operator (which is formally identical with the Landau–Boltzmann plasma equation) is self-adjoint. Also given are several corrections to the hydrodynamic equations presented in the book by Rice and Gray.
H–H* Interactions: The Adiabatic Polarization of H by H*
Authors: Ritchie A. B.
Published: February 2004

The method of polarized orbitals of Temkin used for slow electron atom scattering is extended to interactions of the type (H, H*) and (H, p+, e−), where the excited electron is of high principal quantum number if bound or low k if in the continuum. The equation of motion for the excited electron is derived, and the solution written as a partial wave expansion. All direct potentials are calculated, and applications are discussed.
Dielectric Studies. XXVI. Relaxation Data and Apparent Dipole Moments of N-Methylaniline, N,N-Dimethylaniline, and N,N-Diethylaniline
Authors: Tucker S. W. , Walker S.
Published: February 2004

Dielectric studies have been carried out at microwave frequencies on dilute solutions of N-methylaniline, N,N-dimethylaniline, and N,N-diethylaniline, and the static dielectric constant has been measured at 2 MHz. N-Methylaniline has been studied at 25 and 50°C in cyclohexane, while N,N-dimethylaniline and N,N-diethylaniline have also been examined in this solvent at 15, 25, 35, and 50°C. N-Methylaniline and N,N-dimethylaniline have been studied at 25°C in 1,4-dioxan solution. Both the mean relaxation time and dipole moment data indicate intermolecular hydrogen bonding between N-methylaniline and 1,4-dioxan of the type NH···O. The dielectric data have been analyzed into contributions from two relaxation times, the longer of which has been identified with reorientation of the molecule. N,N-Dimethylaniline and N,N-diethylaniline yield dipole moments of the same order as that obtained by the non-dielectric absorption methods, whereas N-methylaniline has an appreciably lower moment and thus behaves similarly to aniline and o-, m-, and p-toluidine. The difference in behavior is mainly to be attributed to the presence of intermolecular hydrogen bonding of the type NH···N of the –NH2 and –NHCH3 groups which is not feasible for the –N(CH3)2 and –N(C2H5)2 groups. This leads to an additional higher-frequency dispersion exhibited by primary and secondary aromatic amines which seems (at least in part) to be related to the ability of the molecule to self-associate through forming intermolecular hydrogen bonds.
Scintillation Efficiencies of Cyclohexane Solutions with Varying Solute Concentration
Authors: Horrocks Donald L.
Published: February 2004

Increasing the concentration of scintillator solute in cyclohexane leads to an increase in the relative scintillation yield through the action of the scintillator molecules as electron and positive ion scavengers. In this work the increase was shown to be proportional to the logarithm of the cube root of the solute concentration. This dependency indicates that over the concentration range investigated, 10−3 to approximately 1 mole/liter, the scavenging process differs from the square-root dependence which has often been observed with other electron scavengers.
Hot-Atom Reactions in the Photolysis of Deuterium Chloride at 1849 Å
Authors: Wood Gerry O. , White John M.
Published: February 2004

The importance of hot deuterium atoms in photolyses of DCl–lCl2 mixtures at 1849 Å has been demonstrated, and the kinetics of this system have been described. Photodecomposition of DCl was followed by mass-spectrometric analysis of the D2 formed after successive intervals of time. The observed decreases in the initial rate of D2 formation upon addition of CO2, and inert gases CO2, Xe, and CF4 may be readily interpreted in terms of a hot-atom mechanism but cannot be made compatible with a completely thermal mechanism. Rate coefficient ratios for the hot-atom reactions, D*+DCl→ lim 2D2+Cl, D*+M→ lim 3D+M, D*+Cl2→ lim 6DCl+Cl, were found to be k6 / k2 ≈ 6.5, k3DCl / k2 = 0.65, k3CO2 / k2 = 1.15, k3CF4 / k2 ≈ 1.15, and k3Xe / k2 < 0.1. The ratio k6 / k2 increased from 6.5 in the absence of inert gas to 9.2 when [CO2]/[DCl] = 1.87. This ratio increases to ≈ 300 for a thermal atom distribution at 300°K. Comparisons of thermalizing efficiencies for several molecules suggest that inelastic collisions are important in thermalizing hot atoms produced photochemically at 2.1 eV.
Thermodynamic Properties and the Cohesive Energy of Calcium Ammoniate
Authors: Dickman S. , Senozan N. M. , Hunt R. L.
Published: February 2004

The equilibrium pressure of ammonia over calcium ammoniate, Ca(NH3)6, has been measured at over 40 temperatures extending from − 10 to + 13°C. The standard enthalpy, free energy, and entropy of dissociation, Ca(NH3)6(s)⇌Ca(s)+6NH3(g), per mole of ammonia at 0°C have been determined to be 9.95 ± 0.10 kcal, 1.890 ± 0.010 kcal, and 29.5 ± 0.4 eu, respectively. Combining the enthalpy of dissociation with other thermodynamic data, the energy of the reaction Ca(NH3)6(s)→Ca(NH3)62+(g)+2e−(g) is found to be 234 kcal/mole of calcium ammoniate. Comparison of this value with the predictions of the modified Hartree model indicates that the valence electrons of calcium are more highly delocalized in calcium ammoniate than they are in calcium itself; calcium ammoniate is more nearly an ideal metal than calcium—at least in so far as its cohesive energy is concerned.
Classical Treatment of Vibration–Rotation Intensities of Diatomic Molecules
Authors: Jacobi Nathan
Published: February 2004

The effect of vibration–rotation interaction on line intensities is treated semiclassically. Consideration of this effect enables one to determine the dipole moment function uniquely, and its classical treatment is both simpler and easier to visualize, although less precise, than the quantum-mechanical one. The calculation is performed for the fundamental, first, and second overtone bands, and the second overtone of CO is used as an example for the determination of M3 in the dipole moment function.
Generalized Oscillator Strengths for the 61S→61P1 Transition in Mercury
Authors: Skerbele Ausma , Lassettre Edwin N.
Published: February 2004

The generalized oscillator strengths for the 61S0→61P1 transition in mercury have been determined at 300-, 400-, and 500-eV electron kinetic energy. Extrapolation to zero momentum change gives f0 = 1.11 ± 0.10. This result is in very good agreement with the optical oscillator strength, f0 = 1.18 ± 0.07, which was determined by Lurio using the zero-field level crossing method.
Viscosity of Polar–Quadrupolar Gas Mixtures
Authors: Bhattacharyya P. K. , Ghosh A. K.
Published: February 2004

Viscosities of the polar–quadrupolar gas mixtures, CH3Cl–CO2 and SO2–CO2, have been measured in the temperature range from − 35–35°C by an oscillating-disk viscometer. The results show that viscosity is not significantly affected by the dipole–quadrupole term in the unlike interactions. Better combination rules than those now available are necessary for accurate prediction of properties of such gas mixtures.
Experimental Study of the Deactivation of Excited H Atoms by Atmospheric Gases
Authors: Shukla R. V. , Jain S. K. , Gupta S. K. , Srivastava A. N.
Published: February 2004

Hα and several other members of the Balmer series of the H atom have been observed in the afterglow of water vapor. The intensity variation of the Hα line with the pressure of H2O, O2, and N2 gases has been studied photometrically. The quenching coefficients of Hα line for these gases have been found to be 1.80 × 10−8, 3.32 × 10−8, and 1.98 × 10−8, cm3 molecule−1·sec−1, respectively.
Polarized Infrared and Raman Spectra of Single-Crystal CsNO3-II
Authors: Melveger A. J. , Khanna R. K. , Lippincott E. R.
Published: February 2004

Polarized infrared and laser-induced Raman spectra were obtained for single-crystal CsNO3-II. The spectra in the region of the internal vibrations of NO3− indicate that these ions are positioned at sites having C1 symmetry, and the unit cell symmetry of the trigonal space group is C31[C3]. Raman spectra of the lattice vibrations are presented.
Calculation of Ion–Molecule Reaction Rate Constants from Ion Cyclotron Resonance Spectra: Methyl Fluoride
Authors: Marshall Alan G. , Buttrill S. E.
Published: February 2004

A general method is given for obtaining ion–molecule reaction rate constants from low-pressure ion cyclotron resonance signal intensity measurements; the analysis can be applied to any kinetic scheme including those with tertiary and higher-order products. Steps in the analysis include determining the number of ions in a particular region of the analyzer, calculating from the zero-pressure ICR lineshape the power absorption from ions in that region, and then summing such contributions over all regions of the analyzer. To illustrate the analysis, explicit ICR intensity expressions are derived for a kinetic scheme with stable tertiary species. These expressions are used to determine the rate constants for the ion–molecule reactions in methyl fluoride. The resultant rate constants CH3F++CH3F→CH3FH++CH2F, k = 13.6 × 10−10cm3molecule−1·sec−1; CH3F++CH3F→C2H4F++HF+H, k = 0.96 × 10−10cm3molecule−1·sec−1; and CH3FH++CH3F→C2H6F++HF, k = 8.0 × 10−10cm3molecule−1·sec−1 are independent of pressure over the range from 2 to 5 × 10−5 torr. The theory accurately predicts the relative signal intensities in methyl fluoride for each ion up to a pressure of 5 × 10−5 torr, where the tertiary ion signal intensity is 30% of the total intensity of all species present.
Self-Consistent Molecular Orbital Methods. IV. Use of Gaussian Expansions of Slater-Type Orbitals. Extension to Second-Row Molecules
Authors: Hehre W. J. , Ditchfield R. , Stewart R. F. , Pople J. A.
Published: February 2004

Least-squares representations of the 3s and 3p Slater-type atomic orbitals by a small number of Gaussian functions are presented. The use of these Gaussian representations in self-consistent molecular orbital calculations extends our previous study to molecules containing second row elements. Calculated atomization energies, electric dipole moments, and atomic charges are shown to rapidly converge (with increasing number of Gaussians) to their Slater limits. Results of valence shell optimization studies on a series of second-row compounds are nearly independent of the level of the Gaussian approximation, and they allow a set of standard molecular ξ exponents to be proposed.
Widths of Rotational Lines of an Asymmetric-Top Molecule SO2 I. Broadening by a Rare Gas
Authors:   Krishnaji, Prakash Vinod
Published: February 2004

Widths of six rotational lines of SO2 with Ji ranging from 3 to 16 have been measured. Linewidths have been calculated theoretically on the basis of the Anderson theory, and an assessment of the relative importance of different interactions has been made. Calculations have also been done on the basis of the Murphy–Boggs theory. The theoretical and experimental linewidths are found to agree well.
Solubility of Phenanthrene in Compressed Methane, Ethylene, Carbon Dioxide, and Nitrous Oxide: The Correlation of Phenanthrene–Gas Second Cross Virial Coefficients Using Pseudocritical Parameters
Authors: Bradley H. , King A. D.
Published: February 2004

The solubility of phenanthrene in compressed methane, ethylene, carbon dioxide, and nitrous oxide has been measured over pressure ranges of 1–60 atm at temperatures ranging from 37 to 142°C. Second cross virial coefficients representing phenanthrene–gas pair interactions have been evaluated from this data. It is shown that when allowance is made for the effect of molecular quadrupole moments on the critical temperatures of carbon dioxide and nitrous oxide, ordinary combining rules produce pseudocritical parameters which reduce these phenanthrene–gas cross virial coefficients to a single function of reduced temperature. The data are fitted to several potential functions which are shown to be consistent with the reduced behavior of these systems.
Single-Crystal EPR Study of a Cu(II)dialkyldiselenocarbamate. An Example of Noncoinciding Principal Axes
Authors: van Rens J. G. M. , Keijzers C. P. , van Willigen H.
Published: February 2004

A single-crystal EPR study of Cu(II)di-n-butyldiselenocarbamate magnetically diluted in the corresponding Ni(II) complex is reported. The directions of the principal axes of the 63Cu and 77Se hyperfine splitting tensors and the magnitudes of the electron-spin–nuclear-spin dipole–dipole interactions along these axes were found to agree satisfactorily with what is expected for a planar complex of approximately D2h symmetry with one unpaired electron in an antibonding σ orbital. The Se hfs data were used to calculate the extent to which the Se 4s and 4p atomic orbitals participate in the orbital of the unpaired electron. It was found that two principal axes of the g tensor do not coincide with the principal axes of the Cu hfs tensor. In addition, the anisotropy in g value reaches a minimum in the plane where the anisotropy in the Cu hfs reaches a maximum. This indicates that the over-all electronic structure of the complex differs significantly from the structure normally evoked to interpret the EPR parameters of planar Cu(II) complexes, notwithstanding the “normal” hyperfine data. The consequences of the noncoincidence of principal axes for the powder spectrum are discussed. It is shown that the peak positions in the recorded powder spectrum can be accounted for quantitatively using the single-crystal EPR results.
Ionization of Atoms by Collisions with Metastable Helium Atoms
Authors: Matsuzawa Michio , Katsuura Kanji
Published: February 2004

A theoretical calculation for the cross sectionHe(23S)+He(23S)→He(11S)+He++e is carried out using the impact parameter method, and with and without the approximation of straightline trajectory. It is shown that the accuracy of wavefunctions is not so important and the ionization cross section is determined mainly by the interatomic potential between the two colliding particles. The validity of the semiempirical treatment for the process He(23S)+X→He(11S)+X+e by Ferguson, by Bates et al., and by Jones et al. is discussed.