bluuebunny/crossref_metadata_2025 huggingface dataset:
X-band ESR spectrum of nitrogen dioxide
Authors: Burch David S. , Tanttila Walter H. , Mizushima Masataka
Published: February 2004

The ESR spectrum of gaseous NO2 has been studied experimentally over the pressure range 0.05–10 torr at X band for a range of polarizing magnetic field 1.5–8 kG. The spectra are interpreted by a theory which includes the effects of anisotropic electronic and molecular magnetism, intermediate coupling of angular momenta, and centrifugal distortion. Well isolated spectral lines at high magnetic field have been employed to give quantitative information on the electronic g tensor.
Cross sections for direct and charge-exchange excitation in some alkali ion-atom collisions
Authors: Aquilanti V. , Bellu G. P.
Published: February 2004

Absolute total cross sections for inelastic processes in (Li+, Na), (Li+, K), (Na+, K), and (K+, Na) collisions have been measured at ion energies lower than 1.5 keV. Both direct and charge-transfer excitation have been observed. The results are interpreted in terms of the electronic structure of asymmetric alkali dimer ions.
Partitioning of excess energy in dissociative resonance capture processes
Authors: Harland P. W. , Franklin J. L.
Published: February 2004

The translational energies of selected negative ions formed by dissociative resonance capture processes from the polyatomic systems NF3, BF3, CF4, C2F6, C3F8, and c-C4F8 have been measured as functions of excess energy over the resonances. The excess energy in the molecular negative ion intermediate prior to dissociation has been calculated and partitioned into translational, vibrational, and, in some cases, electronic excitation of the dissociation products. The degree of vibrational activation in the intermediate state before dissociation is found to depend on the particular molecule under investigation and to vary from one dissociation channel to another. These observations are discussed in relation to theoretical concepts of dissociative resonance capture and given a qualitative explanation. The measurement of translational energy has led to a more complete interpretation of the states involved in the various processes and in computing ground state thermochemical properties of the decomposition products.
The repulsive Σg+1 He2 potential obtained from total cross sections
Authors: Foreman P. B. , Rol P. K. , Coffin K. P.
Published: February 2004

An improved apparatus for obtaining short-range intermolecular potentials is described. The measured ground state He–He potential in the range 0.49 ≤ r ≤ 1.56 Å is V(r) = (215.3±9.4) × exp[−3.950±0.044)r] eV. This agrees extremely well with the results of molecular orbital theory, whereas earlier experiments were 25% lower, and is confirmed by a recent independent measurement in the range 0.9–1.5 Å. A comparison is also made with statistical model calculations.
Dielectric constant, refractive index, atomic polarization, and dipole moment derivatives of hexamethylenetetramine-h12 and -d12
Authors: Bertie John E. , Solinas Marco
Published: February 2004

The frequencies of the longitudinal and transverse components of the infrared-active modes of hexamethylenetetramine-h12 and -d12 have been used to determine the static dielectric constant and the dipole moment derivatives, using the refractive index. The sodium-D refractive index and the static dielectric constant of HMT-d12 are the same as those of HMT-h12, within experimental error. The static dielectric constant is 2.67±0.05 and the atomic polarization is 2.8 ±0.7 cm3. The dipole moment derivatives are listed for seven of the nine infrared-active modes of each molecule.
Vibrational energy levels of an acetylene molecule
Authors: Chang Chen-Fee
Published: February 2004

Pure vibrational energy levels of an acetylene molecule up to second order have been calculated by using a newly proposed labeling scheme of polar harmonics and newly constructed vibrational wave functions. The old energy level expressions emerge as special cases of the newly derived results in this paper.
Ab initio evaluation of the fine structure of the oxygen molecule
Authors: Langhoff Stephen R.
Published: February 2004

The electron spin dipole-dipole and spin-orbit contributions to the zero-field splitting in the O2 Σg−3 ground state are calculated using the correct microscopic Hamiltonians. The calculations are carried out using minimum, double-zeta, and double-zeta-plus polarization basis sets constructed from contracted Gaussian-lobe functions. Configuration-interaction wavefunctions are used for the ground state and all excited states that couple to the ground state via the spin-orbit Hamiltonian. Values of 1.790 and 1.928 cm−1 are obtained for the splitting parameter λ for the double-zeta and double-zeta-plus polarization bases, respectively, in good agreement with the accurate experimental value of 1.981 cm−1. The spin-orbit contribution which comes primarily from the low-lying excited Σg+1 state accounts for about 2/3 of the total splitting. It is observed that only states which are single excitations from the ground state have a significant spin-orbit contribution and that the over-all effect of electron correlation on the parameter λ is less than 10%. A value of λ1, λ1 = [R(dλ/dR)]Re, of 0.746 cm−1 was calculated in comparison to the experimental value of 0.7129±0.0012. The spin-spin and spin-orbit contributions to λ1 were, respectively, −1.478 and 2.224 cm−1.
Pi electron states of the cyclopentadienyl cation: A comparison of complete CI and UHF results
Authors: Purins D.
Published: February 2004

Complete CI pi electron wavefunctions and energy levels are calculated for the cyclopentadienyl cation and compared to the UHF results of Phillips and Schug [J. Chem. Phys. 57, 3498 (1972)]. The projected UHF and CI energies for the lowest singlet (1E2′) and triplet (3A2′) states are in good agreement, but energies of the projected excited states do not correspond to the lowest CI levels of the same symmetry. In the UHF 1E2′ and 3A2′ wavefunctions, the contribution of excited configurations is smaller than in the CI functions.
Visual observation of the critical temperature and density: CO2 and C2H4
Authors: Moldover M. R.
Published: February 2004

The critical temperature (Tc) and density (ρc) of carbon dioxide (CO2) and ethylene (C2H4) have been determined by a modern version of the classical technique of visual observation of the disappearance of the meniscus. We discuss in some detail what a ``visual observation of the disappearance of the meniscus'' is, a subject that is relevant to the possible use of critical temperatures as secondary temperature reference points. For CO2 we find Tc = 30.977±0.004°C and ρc = 0.4678±0.0022 g/cm3. For C2H4 we find Tc = 9.194±0.004°C and ρc = 0.2146±0.0006 g/cm3. The errors quoted for ρc are two standard deviations from a fit to an assumed symmetrical scaling equation of state. The errors quoted for Tc are an ``estimated'' limit of error. A comparison of the values of Tc which we have measured with recent PVT data yields new values for the critical pressures (Pc). We find that Pc = 73.753 bar (72.789 atm) for CO2 and Pc = 50.390 bar (49.731 atm) for C2H4.
Electron impact excitation of metastable states of benzene, toluene, and aniline
Authors: Smyth Kermit C. , Schiavone James A. , Freund Robert S.
Published: February 2004

Electron impact excitation functions for the formation of metastable states of benzene, toluene, and aniline are measured under low pressure conditions (∼1 × 10−5 torr) with an electron energy resolution of 0.3 eV. Considerable evidence is presented for assigning these metastables as the lowest triplet states T1. Each excitation function exhibits several features at low electron energy (4–15 eV), which are interpreted in terms of resonances which decay to give T1 and nonresonant exchange excitation processes. Comparison of these triplet excitation functions with the optical excitation functions for fluorescence (see the preceding paper) indicates that intersystem crossing does not make a major contribution to T1 formation under the present experimental conditions. From time-of-flight measurements a lower limit of 500 μsec is estimated for the lifetime of the lowest triplet state T1 for these three molecules.
Characteristic properties of thermodynamic functions for the theory of localized and nonlocalized adsorption
Authors: Oh Byung K. , Kim Shoon K.
Published: February 2004

The maxima, minima, and inflection points of the thermodynamic functions are calculated from the theory of localized and nonlocalized adsorption. Experimental determinations of the molecular thermodynamic functions, which depend on temperature alone, are discussed. Existing empirical methods of determining monolayer capacity from entropies and isosteric heat are examined. The inflection point of isosteric heat or of differential entropy directly gives monolayer capacity within an error less then 5% for ordinary systems. Similar results obtained for the BET theory are given in the Appendix; it is noted that the inflection point of the isosteric heat occurs at the coverage θ = 1−2c−1.
Proton dynamics in hydrated gallium sulfate
Authors: Thompson R. T. , Kydon D. W.
Published: February 2004

The proton relaxation times in the laboratory, T1, and rotating frame, T1ρ, and the dipolar relaxation time T1D have been measured in hydrated gallium sulfate. A proton to gallium cross-relaxation mechanism has been observed. By employing spin thermometry the previous cw work has been reanalyzed and the existence of the OH3+ group confirmed.
Quantum mechanical transition state theory and a new semiclassical model for reaction rate constants
Authors: Miller William H.
Published: February 2004

An ``exact'' quantum mechanical transition state theory is defined, i.e., a model which invokes the basic transition state idea to calculate the rate of a chemical reaction but which is free of any auxiliary approximations. Most importantly, for example, it is not necessary to assume that the Hamiltonian is separable about the saddle point. It is argued that this model should provide an accurate description of the threshold region of the reaction where quantum effects are most significant. Finally, an even more general model, a new kind of semiclassical approximation, is presented which is essentially a synthesis of this quantum mechanical transition state model and the completely classical trajectory procedure for determining the rate constant; at sufficiently high temperatures, quantum effects become negligible, so that the correct rate constant is obtained; while at low temperature, the correct result is obtained because the transition state model becomes valid.
Chemical CO and CO2 lasers produced from the CH + O2 reaction
Authors: Lin M. C.
Published: February 2004

Strong 5 μm CO laser emission was observed in the flash photolysis (λ≥ 165 nm) of mixtures of O2 and CHBr3 in the presence of large amounts of diluent (SF6, Ar, or He). About 60 vibration-rotation transitions were identified in the range between Δν = 14→13 and 2→1. The laser intensity was found to vary linearly with flash energy. The effects of various additives (He, Ar, SF6, CO, N2, N2O, and CO2) were investigated. The stimulated emission is concluded to result primarily from the four-centered reaction CH+O2→ lim 1CO†+OH†,Δ H10=−159 kcal/mole. Other possible minor reactions were also considered. No OH emission was detected under the same experimental conditions. With the aid of a band-pass filter (8.6–15 μm range), 10 μm CO2 emission was observed concurrently with the 5 μm CO emission. The CO2 emission, which consisted of the P(58)–(70) lines of the (001)→(020) band, was found to vary strongly with the partial pressure of O2. Since both the intensity of this emission and the yield of CO2 increased linearly with flash energy, the (001) → (020) CO2 emission is believed to be the direct consequence of the following CH+O2 reaction: CH+O2→ lim 10H+CO2†,Δ H100=−184 kcal/mole. This is the first example of lasing from a chemically produced excited polyatomic molecule. When a small amount of N2O or CO2 was added to the O2–CHBr3–He mixture, the regular (001)→(100) band of both molecules began to lase at ∼P(18)–P(28), presumably resulting from the energy transfer process OH†+M(000)→OH+M(001), where M = CO2 or N2O.
Transferability of electron pairs between H2O and H2O2
Authors: Levy Mel , Stevens Walter J. , Shull Harrison , Hagstrom Stanley
Published: February 2004

The transferability of strongly orthogonal geminals between H2O and H2O2 is investigated. Wavefunctions for H2O are constructed from the appropriate geminals in H2O2. Likewise, except for optimization of the oxygen-oxygen bond geminal (ΛOO), wavefunctions for H2O2 are constructed from the appropriate geminals in H2O. The results are encouraging. In all cases, the energies of the wavefunctions constructed from the transferred geminals are actually lower than the energies of the optimum MO wavefunctions and are close to the energies of the optimum geminal wavefunctions. The optimum geminals of H2O are compared with those of H2O2. The corresponding geminals are found to be almost identical. Some factors which influence the success of geminal transferability are examined. In particular, a view of geminal localization is presented, and shielding and inductive effects are discussed. Owing to substantial shielding of the secondary oxygen nucleus in H2O2, the effective fields seen by the OH geminals turn out to be quite similar in the two molecules. The slight change in the structure of ΛOH that occurs in going from H2O to H2O2 is compatible with the slight difference in the effective field associated with ΛOH in H2O2 as compared to H2O. This effective field difference is reflected in a small kinetic energy (bond energy) change for ΛOH.
Brillouin and Rayleigh scattering in polybutadiene
Authors: Huang Y. Y. , Wang C. H.
Published: February 2004

Light scattering studies of polybutadiene from 110 to 350°K reported herein include measurements of Brillouin shift, Brillouin linewidth, and Rayleigh depolarization ratios as functions of temperature. The hypersonic attenuation coefficient over one wavelength (α λs) is insensitive to temperature variation below Tg; above Tg, α λs increases rapidly with increasing temperature. The sound attenuation theory of Woodruff and Eihsenreich gives an adequate description of the measure α λs value below Tg; no quantitative theory describes the sound attenuation above Tg. The Krishnan effect, depolarization ratio ρn = Vh/Hn ≠ 1, was observed for polybutadiene below 250 °K. The frozen-in density fluctuation mechanism proposed by Mueller fails to explain the effect; frozen-in fluctuations of the dielectric anisotropy are a possible mechanism.
Theory of line narrowing by double-frequency irradiation in NQR
Authors: Grigolini P.
Published: February 2004

It is shown that the standard time-dependent perturbation theory is inadequate to treat the problem of line narrowing by double-frequency irradiation in NQR. We show here that a semiclassical treatment which avoids the secular terms provides results in agreement with the radiation field quantization method, which is here extended for the first time to NQR problems. As an application, we consider a hypothetical 14N NQR double irradiation experiment and we determine the conditions which lead to line narrowing.
Monte Carlo studies of the fluid-solid phase transition in the Lennard-Jones system
Authors: Streett William B. , Raveché Harold J. , Mountain Raymond D.
Published: February 2004

Monte Carlo calculations for 108- and 256-particle Lennard-Jones systems have been carried out at 140 temperature-density points in the vicinity of the fluid-solid phase transition. Several types of initial configurations have been used, including fcc lattice arrays, disordered arrays, and combinations of lattice and disordered arrays. The results of runs at high densities show that for small periodic systems the calculations are dependent on the initial configuration and that such systems can exist in many different metastable states from which minimum energy states are not accessible in runs of the order of 106 to 107 configurations. In the vicinity of the smallest density at which the fcc lattice is stable, the calculated pressure-volume curve exhibits many of the features of a ``van der Waals loop''; however, because a single phase is thermodynamically unstable over part of this region, the loop cannot be completely resolved through machine calculations. The use of the van der Waals loop to estimate the melting parameters for the Lennard-Jones system leads to fluid and solid densities 3% to 4% lower than those calculated by the indirect method of Hansen and Verlet.
Freezing and melting properties of the Lennard-Jones system
Authors: Raveché Harold J. , Mountain Raymond D. , Streett William B.
Published: February 2004

Using Monte Carlo simulations, we investigate average molecular arrangements that occur with the fluid-solid transition in a classical Lennard-Jones system. The crystalline order of the solid phase is explicitly shown by the angularly averaged molecular correlation functions which, in the solid, exhibit a behavior not observed in the fluid. The pair and triplet correlation functions delineate the crystalline pattern of the ordered phase out to internuclear separations of many nearest-neighbor distances. A molecular criterion for freezing is reported which claims a proportionality between the values of the pair correlation function in the fluid at the positions of the first and second nearest neighbors. The general behavior of the triplet correlation function in the fluid phase is interpreted. We also compare predictions for melting pressures and the densities of the coexisting fluid and solid phases.
Optical studies of the products of charge exchange between He+ and CO
Authors: Coplan M. A. , Ogilvie K. W.
Published: February 2004

The optical emission from the A-X and B-X transitions of CO+ produced by charge exchange collisions between He+ and CO have been examined over the incident ion energy range 500 to 1500 eV. Absolute excitation cross sections for the transitions were measured from 200 to 1500 eV and compared with measurements of the total charge exchange cross section. To account for the difference between the two sets of measurements, amounting to a factor of 30 at low ion energies and a factor of 4 at higher energies, alternate reactions are proposed.
Correlated wavefunctions, energies, and one-electron radial densities for S states of the He atom
Authors: Winkler P. , Porter R. N.
Published: February 2004

A priori approximation of integral-transform wavefunctions by Gauss quadrature provides an efficient and simple method for obtaining a finite approximation to the complete set of eigenfunctions of the Hamiltonian of a two-electron atom. These functions are described, and the energies and one-electron radial densities of the lower-lying S states of the He atom and the. ground state of H− are given. The energies are close to the exact values obtained from conventional variational results with Hylleraas-type functions extrapolated to the limit of an infinity of terms. The one-electron radial densities of the S states of He are found to have n −2 pseudonodes, where n is the principal quantum number, the triplet-state pseudonodes lying slightly closer to the origin than those of the corresponding singlet states.
Merging beams study of the reaction H2+ (D,H) HD+
Authors: Wendell K. L. , Rol P. K.
Published: February 2004

The merging beams technique was used to study the reaction H2+ (D,H) HD+ in the energy range of 0.05–12 eV. The cross sections for the reaction have been measured in the range 0.05–5 eV, and at 2 eV there is good agreement with trajectory surface hopping calculations. The diatomic product is scattered forward with respect to the direction of the neutral beam in the c.m. coordinate system over the entire energy range. The relative kinetic energy of the products is nearly equal to the relative kinetic energy of the reactants.
Exact ground and excited state second-order properties of the hydrogen atom. I. Polarizabilities
Authors: Laurenzi Bernard J. , Williams Daniel G. , Bhatia Gertrude Stuchlik
Published: February 2004

Using the exact generalized Green's functions for the first three energy levels of the hydrogen atom, we have computed the static dipole polarizabilities for the S states. The calculations were done analytically and exactly on a digital computer using the list-processing language LISP.
Depolarized Rayleigh scattering and 13C NMR studies of anisotropic molecular reorientation of aromatic compounds in solution
Authors: Bauer D. R. , Alms G. R. , Brauman J. I. , Pecora R.
Published: February 2004

Measurements of reorientational relaxation times of simple aromatic compounds have been made by both depolarized Rayleigh light scattering and 13C NMR spin-lattice relaxation. Combination of the reorientation times determined by these techniques makes it possible to extract the reorientation times about the different molecular axes. The viscosity dependence of reorientation times about the individual molecular axes has been measured for benzene, mesitylene, toluene, and nitrobenzene. The viscosity dependence, which is highly anisotropic, is discussed in terms of a ``slip'' model of reorientational motion.
Europium in the ultraphosphate lattice: Polarized spectra and structure of EuP5O14
Authors: Brecher C.
Published: February 2004

The polarized emission and absorption spectra of single crystals of europium ultra(penta)phosphate, EuP5O14, were measured and interpreted. Most of the observed transitions were identified and the energy level structure of the 7F multiplet defined. The over-all site symmetry is found to be extremely low (C1), but in the immediate vicinity of the Eu3+ ion the local symmetry appears to deviate little from C2v. Crystal field calculations were performed for such symmetry and gave a respectable fit to the observed Stark splittings of the 7F multiplet. A simple structural model for the first coordination shell of the Eu3+ ion is proposed, consistent with the spectroscopic behavior and with the signs and relative magnitudes of the calculated crystal field parameters. Finally, the decay times of the 5D0 and 5D1 emitting states of the ion were calculated and found to be consistent with measurement.
Raman spectra and out-of-plane ring vibrations of bicyclo [3.1.0] hexane and its analogs
Authors: Lewis J. D. , Laane J. , Malloy Thomas B.
Published: February 2004

The low-frequency vapor phase Raman spectra have been recorded for bicyclo[3.1.0]hexane, 3-oxabicyclo[3.1.0]hexane, 6-oxabicyclo[3.1.0]hexane, and 3,6-dioxabicyclo[3.1.0]hexane. From the six observed ring-puckering transitions for bicyclo[3.1.0]hexane, the ring-puckering potential energy function was determined to be V(cm−1)=24.70(Z4+25.72Z2+ 9.28Z3), where Z is the reduced ring-puckering coordinate. For each of the oxabicyclohexanes three transitions were observed for the puckering mode and these were in agreement with previously reported far-infrared spectra. No puckering transitions were observed for the dioxabicyclohexane. For each of the four molecules, frequencies corresponding to twisting of the five-membered ring and rocking of the three-membered ring were also observed.
Thermal expansion of α-trinitrotoluene from 77 to 273 K
Authors: Heberlein D. C.
Published: February 2004

Relative length changes in orthorhombic crystals of α-TNT have been measured from 77 to 273 K. Using a three-terminal capacitance technique, length changes were measured with a resolution of 10−9 cm under optimum conditions. Relative temperature changes of 1 part in 105 were detected with a platinum resistance thermometer used as one arm of an ac resistance bridge. The linear expansion coefficient calculated from these data is found to have a second-order transition with a critical temperature, Tc = 211.7 K. Mangelsdorf plots indicate logarithmic behavior of the linear expansion coefficient along all crystalline axes for the temperature intervals 203 K < T < Tc and 223 K < T < Tc. The volume expansion coefficient was obtained from the three linear expansion coefficients.
Magic-angle carbon-13 NMR study of CO2 adsorbed on some molecular sieves
Authors: Stejskal E. O. , Schaefer Jacob , Henis J. M. S. , Tripodi M. K.
Published: February 2004

Carbon-13 NMR spin-lattice relaxation times of isotopically enriched CO2 adsorbed on a variety of channel and cavity molecular sieves have been obtained. At room temperature, the spin-lattice relaxation of adsorbed CO2 is dominated by paramagnetic impurities in commercial molecular sieves with critical cage dimensions less than about 8 Å, but by spin rotation in some sieves with larger cage dimensions. Asymmetric 13C line shapes are generally observed for CO2 adsorbed in these molecular sieves. This asymmetry is, for the most part, independent of the presence of paramagnetics, but is instead generated by the local microscopic magnetic susceptibility heterogeneities of the host sieve. Substantial narrowing of the asymmetric lines can be achieved by magic-angle spinning. For CO2 adsorbed on Na+-mordenite, spinning experiments at 3 kHz reveal only a single symmetric line, consistent with the great majority of CO2 molecules in the system being physi- rather than chemisorbed.
Mössbauer effect study of the deuterated and hydrogenated hydrates of ferrous chloride
Authors: Brunot Bernard
Published: February 2004

A detailed study of isotope effects on Mössbauer hyperfine parameters is presented. Isomer shifts and quadrupole splittings for FeCl2 · n H2O and FeCl2 · n D2O, where n = 1, 2, 4, and 6, were measured between 90 and 273°K. Identical isomer shifts δ were observed for the mono-, tetra-, and hexahydrates. Concerning the dihydrates, different δ were found with parallel temperature dependence. For the four studied hydrates, different quadrupole splittings ε were measured for the deuterated and the hydrogenated compounds. The temperature dependence of δ and ε were briefly analyzed with reference to structure and chemical bond considerations. A summary study of Debye-Waller factors suggested that a comparative investigation of lattice dynamics for the deuterated and hydrogenated hydrates is possible.
Interionic forces and ionic polarization in alkaline earth halide crystals
Authors: Yuen P. S. , Murfitt R. M. , Collin R. L.
Published: February 2004

Ionic force parameters for a soft sphere model have been derived from the known crystal structures and thermodynamic lattice energies of alkaline earth halides. Polarization of the chloride, bromide, and iodide ions has been taken into account by a simple shell-core model. The derived parameters are capable of reproducing the crystal structures of the alkaline earth halides to within a root mean square deviation of under 3% in interionic distance. Ionic polarizabilities are in rough agreement with those deduced for crystal ion polarizabilities by other means but are smaller than the commonly accepted values in all cases.
Vibrational excitation of ozone formed by recombination
Authors: von Rosenberg C. W. , Trainor Daniel W.
Published: February 2004

A new facility coupling flash photolysis and time resolved ir detection and uv absorption diagnostics is described. Its application to studying the reaction O+O2+M→ lim (1) O3†+M followed by O3†+M→ lim (2)O3+M with M=O2 or N2 and where O3† denotes vibrationally excited ozone is described. Our results give k1=3×10−34 cm6 sec−1, k2=2×10−14 cm3 sec−1, φ(ν1)+φ(ν3)=1.6, and φ(ν2)=3.7, where φ(νi) is the average number of quanta of energy νi, resulting in mode νi from each recombination (ν1,2,3=1103, 701, 1042 cm−1). This partitioning of the product energy accounts for 50% of the 25 kcal exothermicity of the recombination. These results are peculiar to the model used for interpretation, which is discussed in some detail in the text.
Double resonance study of relaxation in nitric oxide
Authors: Nachshon Yehuda , Coleman Paul D.
Published: February 2004

A double resonance technique, employing a pulsed transverse HF laser to pump the ν =0→2 level of the 2Π1/2 ground electronic state of NO and a CW electrically excited CO laser to probe the ν =1→2 and ν =2→3 levels of both the 2Π1/2 and 2Π3/2 states of NO, was used to determine the V-T rate constant k10 and estimate the V-V and spin relaxation rates. The value of k10 for the process NO(1)+NO(0)→2NO(0) was found to be 2.6±0.2×103 torr−1 · sec−1 at 295°K.
Vibrational relaxation of HF(v = 1) and DF(v = 1) by H2 and D2
Authors: Bott Jerry F.
Published: February 2004

The vibrational relaxation times of DF(v = 1) in the presence of H2 have been measured in a combined shock tube laser-induced fluorescence experiment at temperatures from 440 to 690°K and 295°K. The data fall along an extrapolation of previously obtained high temperature shock tube data. Data are presented also for the relaxation of HF(v = 1) by H2 and DF(v = 1) by D2.
Compression and anharmonicity of rare-earth metals
Authors: Reynolds C. L. , Barker R. E.
Published: February 2004

In a recent paper Gust and Royce have presented some equation of state data and given evidence of an electronic interaction during the compression of the rare-earth metals. We have shown that their data are in agreement with an anharmonicity postulate and the coefficients in the compression equation, −Δ V/V0 = a 1p + a 2p2 + a 3p3, have been calculated. The anharmonicity coefficient C2≡ a2/a12, was found to be −1.58.
Resonance Raman spectra of copper-porphin
Authors: Verma A. L. , Bernstein H. J.
Published: February 2004

Resonance Raman spectra of copper-porphin in solution have been obtained using the tunable rhodamine 6G dye, Ar+, and HeCd lasers for excitation. Several bands show variation of intensity with excitation wavelength and many combination and overtone bands have been observed with 5145 Å excitation. Depolarization ratios for the two anomalously polarized bands [ρl > (3/4)] at 1322 and 1587 cm−1 remain constant (∼45) with all the exciting wavelengths in the α and β absorption regions while some polarized bands show variation of their ρl values. It is shown that the rigorous molecular symmetry of Cu-porphin in solution is D4h. Symmetry species of the vibrational modes have been assigned.
Intensities in the x-ray photoelectron spectra and electronic structures of the oxyanions of Si, P, S, Cl, Mn, and Cr
Authors: Prins R.
Published: February 2004

X-ray photoelectron spectra of the valence region of the lithium salts of SiO44−, PO43−, SO42−, ClO4−, ClO3−, ClO2−, SO32−, S2O32−, MnO4−, and CrO42− have been measured. With the aid of molecular orbital calculations and available x-ray fluorescence data an assignment is given of the photoelectron lines. The line intensities are analyzed with the aid of an LCAO-type model that relates the molecular-orbital photoionization cross sections to atomic-orbital photoionization cross sections and atomic populations in the molecular orbitals. The required atomic cross sections have been obtained from the valence photoelectron spectra of MgO, LiCl, S, P, and Si. The intensity model is shown to give a satisfactory interpretation not only of the trends in the spectra but also of the absolute intensities. Both intensities and energies of the high-binding-energy photoelectron lines demonstrate that the contribution of the oxygen 2s orbitals to the bonding in the main group oxyanions increases with increasing atomic number of the central atom and is especially important in the ClOn− anions. The increase in the e, 3t2 − t1 energy splitting from SiO44− to ClO4− is due to increased π backbonding between the oxygen 2p and central atom 3d orbitals. The intensities of the low-binding-energy lines of CrO42− and MnO4− show that the e and 3t2 orbitals of these anions have appreciable metal 3d character.
Thermodynamics of ternary systems. Quasichemical approximation and the excess ternary term
Authors: Hagemark K. I.
Published: February 2004

Based on the quasichemical theory, second order expressions in terms of the nearest-neighbor interaction parameters are given for the molar energy of mixing, ΔE, and the partial molar excess free energy of mixing, ḠCE, of a ternary system. In order to improve the applicability, the quasichemical binary contributions are replaced by the experimental binary values. The ``leftover'' term or the ``excess'' ternary term is discussed in more detail. The quasichemical theory suggests the ternary excess energy term is of a more complex form than N AN BNC × const. The expressions are useful in calorimetric work and in discussing phase stabilities (miscibility gaps).
Dye laser two-photon excitation study of several 0,0′-bridged biphenyls
Authors: Drucker Ronald P. , McClain W. M.
Published: February 2004

Polarized dye laser two-photon excitation spectra are reported for the following series of 0,0′-bridged biphenyls: fluorene, dibenzofuran, dibenzothiophene, carbazole, and phenanthrene. Two-photon polarization selection rules are used to assign the peaks observed. Several new states are reported and a number of tenuous assignments in the literature are confirmed. The spectra of the bridged compounds are compared with the biphenyl two-photon spectrum.
Long wavelength electromagnetic fluctuating interactions between macroscopic bodies
Authors: Fornés J. A. , Goscinski O.
Published: February 2004

The interaction force between two semi-infinite dielectric media separated by a third one is derived using a method of Rytov. Comparison is made with Green's function results of Dzyaloshinskii et al. Certain limiting procedures of their work are avoided by making a central physical assumption.
Theoretical studies of molecular ions. Vertical ionization potentials of hydrogen fluoride
Authors: Smith Wesley D. , Chen Tsung-Tai , Simons Jack
Published: February 2004

The 2Π and 2Σ+ vertical ionization energies of hydrogen fluoride are studied within the framework of an equations-of-motion approach, which permits the direct calculation of the ion-molecule energy differences. The contributions of charge redistribution and correlation energy change to the calculated ionization potentials are evaluated. The computational efficiency of the method is illustrated and comparisons are made with recent photoionization experimental results.
The inelastic scattering of He and Ne from a (001) surface of sodium fluoride
Authors: Mason B. F. , Williams Brian R.
Published: February 2004

The inelastic scattering of He and Ne atoms from a cleaved (001) surface of NaF has been studied at different surface temperatures. The study was similar to that for the He–LiF system, in that the intensity of the inelastic streaks in the vicinity of diffraction peaks was explored as a function of detector location and crystal rotation. For diffraction peaks not too close to the normal the phonon emission and absorption effects separated into regions on either side of the elastic peak, the latter events being on the side closest to the normal. At 140°K the phonon absorption events were less probable than phonon emission events, i.e., atoms tended to lose energy while at higher surface temperature the probability of energy gain increased. The positions of the streaks moved predictably in space by varying the incident momentum of the beam, a parameter which also influenced the intensity of the streaks. Comparisons have been made to the He–LiF system using the elastic constants of the two materials.
Interactions among the lower valence states of the OH radical
Authors: Smith Wm. Hayden , Elmergreen Bruce G. , Brooks Neil H.
Published: February 2004

In order to define the origins of experimentally observed predissociations within the A2Σ+ state of OH, we have computed overlaps of the bound level vibrational wavefunctions in the A2Σ+ state with the vibrational continua of states of OH arising from the ground electronic state separated atoms. Rapid variation of overlap with rotational quantum number is found to occur for the a4Σ− and X2Πi states with the A2Σ+ state. The resulting predissociation widths are compared with the experimental data, and shown to be able to reproduce it by assuming that the a4Σ− state dominates in radiationless depopulation of the OH A2Σ+ state. The dependence of the transition moment upon internuclear distance is derived, and compared with previous results. Implications of this analysis in terms of the two body formation of OH are indicated.
Visible chemiluminescence from supersonic mixing metal-oxidant flames
Authors: Johnson S. E. , Scott P. B. , Watson G.
Published: February 2004

Intense visible chemiluminescence has been produced by injecting oxidants into a supersonic flow of metal vapor in an argon gas carrier. The metals aluminum, boron, barium, carbon, copper, magnesium, silicon, strontium, titanium, uranium, tungsten, and zirconium have been reacted with one or more of the oxidants oxygen, nitrous oxide, chlorine, and fluorine. A spectral survey is summarized herein and representative spectra are presented and discussed. The powder shock tunnel apparatus developed for these studies is briefly described. We emphasize its unique suitability to visible chemical laser studies as its high active species density enhances the available gain and the high flow velocity aids by sweeping the cavity of poisoning deexcited species.
An ionicity scale based on x-ray photoemission valence-band spectra of ANB8−N and ANB10−N type crystals
Authors: Kowalczyk S. P. , Ley L. , McFeely F. R. , Shirley D. A.
Published: February 2004

A quantitative scale of ionicity based on x-ray photoemission studies of the valence-band density of states of many ANB8−N and ANB10−N crystals is discussed. The scale is empirical. It involves allocating the energy splitting of the two most tightly bound valence-band peaks between covalent and ionic contributions. Several ternary alloys and chalcopyrite-type crystals were also included in this study. The scale was found to be superior to the molecular orbital approach of Coulson and the thermochemical scale of Pauling because of the symmetrical treatment of covalent and ionic contributions. It appears to have wider applicability than the Phillips-Van Vechten scale. The strengths and weaknesses of the proposed scale are discussed.
Vacuum uv photolysis of N2O
Authors: McEwan M. J. , Lawrence G. M. , Poland H. M.
Published: February 2004

Emission from N2 B(3Πg) and O(1S) produced during vacuum uv irradiation of N2O was studied as a function of the wavelength of the incident radiation. Two different processes were responsible for producing N2(B 3Πg) close to its production threshold. One process formed B 3Πg molecules directly and one indirectly via an unidentified precursor having a lifetime ∼27 μsec. The quantum yield of O(1S) atoms produced by photodissociation of N2O was determined as a function of incident photon energy. This yield is near 100% at 129 nm.
Evaluation of configuration coordinate parameters from high pressure optical data. I. Phenanthrene, anthracene, and tetracene
Authors: Okamoto B. Y. , Drickamer H. G.
Published: February 2004

A configuration coordinate model has been developed which relates the shift of optical absorption and emission peaks with pressure and the changes of half-width with pressure to the change in volume of the system upon electronic excitation, Δ, the ratio R of force constants of the excited and ground states, and the coupling of the force constant to the bulk modulus of the surroundings. The configuration coordinate which couples most strongly to the pressure is an inter molecular one. The analysis is applied to phenanthrene and anthracene in the crystalline state, in PMMA, and in hexane. Some data are also presented for crystalline tetracene, for anthracene in methanol and glycerol, and for benzene in hexane and water. Evaluation of these parameters by various combinations of absorption and emission data give consistent results within the precision of the data. The volume contraction upon excitation is significantly larger for anthracene than for phenanthrene, consistent with the larger dipole moment and stronger interaction of the 1La state with the surroundings compared with the 1Lb state. The volume contraction varies with the medium depending on the polarizability and compressibility of the medium. The coupling to the surrounding depends strongly on the rigidity of the medium. A brief discussion of the solvent effects in terms of dielectric theory is also given.
Radiationless decay from triplet state biacetyl molecules with selected vibrational energies
Authors: Moss Arthur Zenker , Yardley James T.
Published: February 2004

We report measurements of the intensity and decay rate of phosphorescence from biacetyl vapor excited into the 1Au1 electronic state as a function of additive pressure and excitation wavelength. The loss in phosphorescence intensity at short wavelengths and low additive pressure is interpreted in terms of an efficient 3AuI ↝ 1AgI intersystem crossing. The rate constant for this process has been determined as a function of excess vibrational energy in the 3 AuI state.
13C chemical shift tensor in K2Pt(CN)4Br0.3 · 3H2O
Authors: Stoll M. E. , Vaughan R. W. , Saillant R. B. , Cole Terry
Published: February 2004

Single crystal rotation spectra have been obtained for the 13C resonance in K2Pt(CN)4Br0.3 · 3H2O and the 13C chemical shift tensor determined. The principal values are (relative to the carboxyl carbon in CH3COOH): σ11=261±10 ppm (parallel to C–N bond), σ22 = −48±10 ppm (perpendicular to C–N bond and Pt–Pt chain), and σ33=−10±5 ppm (parallel to Pt–Pt direction). Since the 14N quadrupole interaction is of similar size to the 14N Zeeman interaction in this material, large effects of the 14N quadrupole interaction are observed on the 13C spectra.
EPR spectra of spin labels in lipid bilayers. II. Rotation of steroid spin probes
Authors: Schindler Hansgeorg , Seelig Joachim
Published: February 2004

The spin label method is used to investigate the nature of molecular motion in a liquid crystalline bilayer. The EPR spectra of different spin labels are simulated by means of perturbation theory. Using the diffusion model with a restoring potential the rotational diffusion coefficients for the different spin labels are evaluated from the linewidth. Rotational diffusion and viscosity are related by a modified Stokes-Einstein-Perrin formula. The correction factors account for the difference between the effective viscosity during rotation and the (translational) viscosity and are interpreted in terms of the geometry and the ordering of the spin probes. The bilayer viscosity η is found to be 3.7 cp ≤ η ≤ 5.7 cp.
Structural strain in small prenucleation water clusters
Authors: Hagen Donald E.
Published: February 2004

A method is developed for incorporating strain energy into a microphysical treatment of small prenucleation water clusters. The molecules are arranged in a clathrate-cage structure, and this structure is allowed to relax to minimize the strain energy resulting from hydrogen bond stretching and bending. The method is applied to various cluster sizes up to 130 molecules and the results are compared with the classical liquid drop model. The effect of anharmonic terms in the interaction is included.
Shear viscosity and order parameter dynamics of fluids near the critical point
Authors: Oxtoby David W. , Gelbart William M.
Published: February 2004

We present a simple modification of the mode-coupling equations which relate the shear viscosity to the decay rate of order parameter fluctuations of simple fluids and binary mixtures near their critical points. By including the background Rayleigh linewidth in these equations, both the critical shear viscosity and the critical Rayleigh linewidth can be calculated with no adjustable parameters, using only background transport data and static critical properties. Our predictions are found to be in good agreement with presently available experimental data.
Interpretation of Raman spectra of van der Waals dimers in argon
Authors: Frommhold Lothar
Published: February 2004

The rotational and vibrational eigenenergies of all bound and predissociating states of the Σg+Ar2 dimer are computed, together with certain averages of the nuclear wavefunctions needed for the computation of the Raman intensities for each transition. The MSV III potential of Parson, Siska, and Lee is used. With this information the complete rotational and vibration-rotation Raman spectra of the argon van-der-Waals molecule is obtained and found to consist of truncated and superimposed line sequences. They are thus characteristically different from such spectra of ordinary molecules. A theoretical ``low-resolution'' spectrum is obtained by superposition of approximated instrumental profiles for each line in the spectrum. At the lowest temperature (103°K) of the experiment nearly all of the observed intensity distribution is due to the dimer Ar2. At high temperatures (300°K) the experimental spectrum is due largely to the scattering of light by pairs of atoms in fly-by collisions, not to molecules. The Raman intensity maxima at ±8.3 cm−1 shift, therefore, must be explained in terms of the former. The apparent insignificance of the rotation-vibration Raman bands in comparison to the pure rotational bands can be explained by adoption of a simple model for the anisotropy of the polarizability tensor.
Measurement of the rate of excitation and deactivation of OCS(001), N2O(001), CS2(001), and C2N2(00100) using laser excited CO as a pumping source
Authors: Hancock J. K. , Starr D. F. , Green W. H.
Published: February 2004

The laser fluorescence method has been used to measure CO(ν=1) collisional transfer rates in several binary and ternary gas mixtures at 296°K. Excitation of the CO(ν=1) level was achieved using pulsed 4.6 μm radiation from a frequency doubled CO2 laser. The relative inertness of CO molecules towards V→T deactivation greatly facilitates the study of vibrational relaxation rates of the additive species in selected cases. In this paper, intermolecular V→V transfer rates at 296°K are reported for CO(ν=1) with N2O, OCS, SO2, CS2, C2N2, and for CO(ν=2) with CO. In addition, the additive deactivation rates were determined for the following collisional processes: N2O(001) with N2O, CO, Ar; OCS(001) with OCS, CO, Ar; CS2(001) with CS2, CO; and C2N2(00100) with C2N2 and CO.
Proton and deuterium magnetic resonance study of the aqueous nickelous complex
Authors: Granot J. , Achlama (Chmelnick) A. M. , Fiat D.
Published: February 2004

The absorption signals of protons and deuterons in bound and nonbound water molecules in the aqueous nickelous system were observed. From the PMR and DMR measurements, the hyperfine coupling constants were calculated and found to be (1.3±0.1)×105 and (2.0±0.2)×104 Hz, respectively. The spin density at the proton (and deuteron) nuclei was calculated to be (2.9±0.3)×10−5 electrons/a.u.3, in accordance with theoretical expectations. The rate constant at 298°K for the exchange of water was found to be 3×104 sec−1, and the activation energy 12 kcal/mole. The relaxation time of the electron at 243°K, assuming T1e =T2e was found to be 1.9×10−12 sec and the activation ernergy 0.8 kcal/mole. The temperature dependence of the proton transverse relaxation rate was studied. It is suggested that in the absence of chemical exchange the transverse relaxation rate is governed both by the relaxation of the nickelous unpaired electrons and by the diffusional motion of the water molecules. Methods of estimating the diffusional correlation time are discussed.
Interatomic potentials for krypton and xenon
Authors: Barker J. A. , Watts R. O. , Lee Jong K. , Schafer T. P. , Lee Y. T.
Published: February 2004

Accurate potentials for ground state krypton-krypton and xenon-xenon interactions are derived using a wide range of experimental evidence including second virial coefficients, gas transport properties, solid state data, known long-range interactions, spectroscopic information on dimers, and new measurements of differential scattering cross sections. In calculating solid-state properties account is taken of long-range many-body interactions. The use of the potentials permits a critical intercomparison of various kinds of experimental data. A ``corresponding states'' comparison of the shapes of the potentials for different inert gas pairs is given. It is concluded that contributions of overlap-dependent many-body interactions to condensed-phase properties of argon, krypton, and xenon are very small.