bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of the monofluorides of nitrogen, silicon, phosphorus, and sulfur from a molecular orbital study
Authors: O'Hare P. A. G.
Published: February 2004

Self-consistent-field wavefunctions near the Hartree-Fock limit have been computed for the 3Σ states of NF and PF, and for the 2Π states of SiF and SF. Based on a Dunham analysis of the computed total energies, results have been derived for the equilibrium bond lengths and spectroscopic constants. Values of 830 ± 20, 4.7, and 0.0042 cm−1 are predicted for the hitherto undetermined ωe, ωexe, and αe of SF. Computed ionization potentials are in excellent agreement with experiment. Electron affinities of −0.1, 1.1, 1.1, and 1.7 eV are predicted for NF, SiF, PF, and SF, respectively. The dissociation enthalpy D0° of PF is estimated to be 4.65 ± 0.2 eV, and values of 0.25, 0.5, and 0.6 D are suggested for the dipole moments of NF, SiF, and PF, respectively. Dissociation enthalpies of the positive and negative ions have also been calculated. A previously calculated re(OF) has been revised to 1.34 Å.
Critical phenomena in fluids. The Percus-Yevick radial distribution functions
Authors: Mandel Frederic
Published: February 2004

The Percus-Yevick theory is studied in the neighborhood of the critical point for the Lennard-Jones 6:12 potential. It is shown that near the critical point the PY radial distribution functions g(r) display a functional form different from that at other temperatures and densities. The asymptotic behavior and the behavior of the second peak of g(r) are particularly striking.
Magnetic moment of 181Ta
Authors: Erich L. C. , Gossard A. C. , Hartless R. L.
Published: February 2004

The nuclear magnetic moment of 181Ta is measured by NMR of a tantalum solution. For tantalum dissolved in HF/HNO3 broad lines arising from 181Ta nuclei in TaF6− complexes are observed at room temperature. A study of linewidth vs temperature shows motional narrowing of the quadrupole broadened line with increasing temperature. Applying the quadrupolar correction, we obtain a nuclear gyromagnetic ratio for 181Ta of 2π(0.5098 ± 0.0002) × 103 sec−1 G−1 and an uncorrected nuclear moment of 2.342 ± 0.001 nm. The chemical shift correction gives 2π(0.5097 ± 0.0002) × 103 sec−1 G−1 for the nuclear gyromagnetic ratio. Correcting the nuclear moment for core diamagnetism, we get 2.361 ± 0.010 nm.
Absolute measurements of total cross sections for electron scattering by Na2 and K2 (0.5–50 eV)
Authors: Miller Thomas M. , Kasdan Abraham
Published: February 2004

Absolute measurements have been made of total cross sections for the scattering of electrons by sodium and potassium diatomic molecules, over the electron energy range 0.5–50 eV, at temperatures of 405 and 335 °C, respectively, using the molecular beam recoil technique. We find the molecular cross sections to lie about 60% and 33% above the respective sodium and potassium atomic cross sections above 2 eV. The measured sodium and potassium molecular total cross sections range from 305 and 430 Å2, respectively, at 0.5 eV and 85 and 97 Å2, respectively, at 50 eV. The over-all uncertainty in the sodium dimer results is at most 16%, and in the potassium dimer results is at most 20%.
EPR spectra of Cu2+ in single crystals of chabazite
Authors: Chao Chien-Chung , Lunsford Jack H.
Published: February 2004

An EPR study of Cu2+ ions in chabazite single crystals has revealed that the copper is presented in three magnetically inequivalent sites. Copper ions at two of these sites differ only in symmetry axes which are 7° apart. This is believed to be a result of twinning or strain in the crystals. These ions are characterized by g∥ = 2.324, g⊥ = 2.068, A∥ = 0.0159 cm−1, A⊥ = 0.0018 cm−1 and Q = 0.0009 cm−1. They are thought to be in the site 2 position, which is located near the center of the six-membered rings. The symmetry axis of the ions essentially coincides with the symmetry axis of the crystal. Copper ions in the third type of site are less abundant and are in a more isotropic environment which suggests that they are located at the site 1 position in the center of the distorted hexagonal prisms.
Ionic solution theory for nonideal solvents
Authors: Stell G.
Published: February 2004

A statistical-mechanical study is made of the deviations from the primitive model (PM) of an ionic solution. In the PM, the solvent is treated as an ideal continuum that manifests itself only through the appearance of a dielectric constant ε ≠ 1. This paper begins with the introduction of a simple model that complements the PM, the NCDM (no charge-dipole model) in which the granularity of the solvent is treated exactly. A second more realistic model, the EISIM (exact ion-solvent interaction model), is then defined and discussed, as is the limit in which the PM approximation becomes an exact result. Like the PM the EISIM can be used as an ``ideal-solvent'' approximation in which the solvent-solvent interaction is idealized so that it manifests itself only through the appearance of ε. However, in the EISIM the solute-solvent interaction is treated exactly. A cluster expansion for Wn(0), the n -point potential of mean force, is derived and a thermodynamic perturbation theory for the problem is developed; an alternative treatment is also noted in which the mean-spherical approximation can be used to bypass the McMillan-Mayer theory and the attendant necessity for knowing Wn(0), n > 2. The connection between the expressions herein derived and the phenomenologically developed Gurney-Frank picture is pointed out; one term in the EISIM is shown to be identifiable with the solute-solvent contribution to the Gurney cosphere-intersection potential. Part of that term can be further isolated and identified as the exclusion-volume contribution to the cosphere-intersection potential.
Molecular rotational Zeeman effect in HOF, a comparison with H2O, F2O, and other fluorine containing molecules; and dipole moments of HOF and DOF
Authors: Rock S. L. , Pearson E. F. , Appleman E. H. , Norris C. L. , Flygare W. H.
Published: February 2004

The linear and quadratic rotational Zeeman effect in HOF has been observed with a high magnetic field. The magnetic susceptibility anisotropies are 2χaa −χbb −χcc = (−19.6±0.6) × 10−6 erg/G2·mole and 2χbb −χaa −χcc = 12.8±1.2 (the a axis is nearly along the OF bond and the c axis is perpendicular to the molecular plane); the molecular g values are gaa = 0.642±0.001, gbb = −0.119±0.001, and gcc = −0.061±0.001 and the molecular quadrupole moments are Qaa = (0.2±0.4)×10−26 esu · cm2, Qbb = 1.9±0.8, and Qcc = −2.1±1.1. These results are compared with H2O and F2O. The effect of in-plane fluorine substitution on the out-of-plane minus the average in-plane magnetic susceptibility anisotropy, Δχ, is discussed for a number of molecules and additive values are obtained for each successive fluorine substitution for planar molecules. These contributions to Δχ are first fluorine = +4.5±1.2, second F = +2.5±1.1, and third F = +0.6±0.8. These trends are explained in terms of changes in hybridization of the atom to which the fluorine is bonded. These values are used with results on mono- and difluorobenzene to estimate Δχ for benzene and trifluorobenzene. The electric dipole moments were obtained by the Stark effect and are HOF: μa = |0.37|±0.10 and μb = |2.20|±0.10. The total electric dipole moment of HOF is μ = |2.23|±0.10 D. The electronic structure of HOF is discussed in light of these results.
ESR spectrum and structure of the n -propyl radical
Authors: Adrian Frank J. , Cochran Edward L. , Bowers Vernon A.
Published: February 2004

We have observed the electron spin resonance (ESR) spectrum of the n -propyl radical in argon at 4 °K, following its production by the photolysis at 2537 Å of n -propyl iodide in the argon matrix. The spectrum is much better resolved than previously observed spectra of this radical, and thus could be analyzed in detail to obtain the following complete set of magnetic constants for the radical: g1 = 2.00290, g2 = 2.00302, g3 = 2.00249; A1(α) = −28.7. A2(α) = −17.8, A3(α) = −21.0 Oe; and A1(β) = 37.7, A2(β) = 33.3, A3(β) = 33.9 Oe. Axis 1 is the CβCα bond, and the plane determined by axes 1 and 2 approximately bisects the β-CH2 bond angle. Comparison of the observed hyperfine structure (hfs) constants with calculated values shows that the radical is rapidly reorienting between approximately equivalent conformations in which the α-CH2 plane makes angles of approximately ± 30 ° with the 1–2 plane of the principal axes of the magnetic tensors. However, a small triplet splitting (5 Oe) of the center line of the spectrum indicates that the β protons, and thus the aforementioned conformations of the radical, are not exactly equivalent. The outer lines of this triplet can be accounted for if certain radicals are reorienting either between a pair of conformations in which the α-CH2 plane makes angles of 35 ° and − 15 ° with the 1–2 plane (state I) or between the pair of conformations with angles of 15 ° and − 35° (state II), which pairs of conformations are equivalent except for an interchange of the β-proton hfs constants. The center line of the triplet can be explained if either some but not all of the radicals occupy matrix sites which permit rapid reorientation between states I and II, or if there is tunnelling between states I and II at a frequency of the same order of magnitude as the difference between the β-proton hfs constants in a single state. As a sidelight to this study, we observed the ESR spectrum of the ethyl radical. The resulting hfs constants for ethyl are in good agreement with those obtained by McDowell et al., and, in addition, we obtained the following components of the g factor tensor: g∥ = 2.00268, and g⊥ = 2.00273, where the parallel axis is the CC bond.
Absolute rate constant for the O + NO chemiluminescence in the near infrared
Authors: Golde Michael F. , Roche Aidan E. , Kaufman Frederick
Published: February 2004

Infrared chemiluminescence from the process O + NO (+ M) → NO2 + h ν (+ M) has been studied between 1.3 and 4.1 μm. The wavelength dependence of the continuum between 1.3 and 3.3 μm is in fair agreement with previous studies and the measured radiative rate constant at 1.51 μm, I1.510 = I1.51 / [O][NO], of (2.4 ± 0.8) × 10−17 cm3 sec−1 · μm−1 establishes the NO–O glow in this spectral range as a secondary emission standard. Comparison with previous studies of the visible region of the glow implies that the over-all radiative rate constant Io lies in the range (9.4–11.2) × 10−17 cm3 sec−1. In the region 3.3–4.1 μm, the previously observed broad band, peaking at 3.7 μm, shows a complex kinetic dependence on [O] and [M].
Radiative lifetimes and pressure dependence of the relaxation rates of some vibronic levels in N2+, N2, CO+, and CO
Authors: Dotchin L. W. , Chupp E. L. , Pegg D. J.
Published: February 2004

Radiative lifetimes of the B2Σu+(ν′ = 0) level in N2+, the C 3πu (ν′ = 0, 1, 2) levels in N2, the B1Σ+(ν′ = 0) and C1Σ+(ν′ = 0) levels in CO, and the B2Σ+(ν′ = 0, 1) levels in CO+ have been measured to be 60.4 ± 0.4, 40.4 ± 0.5, 40.6 ± 0.5, 38.5 ± 0.6, 23 ± 3, 2.2 ± 0.8, 53.6 ± 0.7, and 64.1 ± 0.8 nsec, respectively. The measurements were made by studying the time distribution of photons emitted in the decay of these levels after collisional excitation by a pulsed-proton beam. The apparent lifetime of the levels was studied as a function of target pressure over a range 1–200 mtorr. Collisional quenching and resonance trapping were observed in varying degrees. The radiative lifetimes are derived from the extrapolated zero pressure relaxation rates, and ν′ - progression transition probabilities are determined by using our measured B-A and C-A electronic branching ratios in CO, and the CO+ band strength measurements of Judge and Lee.
Exact solution of the mean spherical model for simple polar mixtures
Authors: Adelman S. A. , Deutch J. M.
Published: February 2004

Wertheim's solution of the mean spherical model (MSM) for pure fluids composed of hard spheres with embedded dipoles [J. Chem. Phys. 55, 4291 (1971)] is extended to multicomponent polar fluid mixtures. The components are restricted to have equal hard sphere radii but may have different dipole moments. The anisotropic part of the pair correlation functions for an m-component fluid characterized by hard sphere diameter d, temperature parameter β, dipole moments μ1, μ2, ···,μm, and densities ρ1, ρ2, ···,ρm are shown to be expressable in terms of the corresponding functions for an effective pure MSM polar fluid with the same hard sphere radius and the same temperature parameter but with an effective dipole moment μ̂ = [m−1 (μ12 + μ22 + ⋯ + μm2)]1/2 and an effective density ρ̂ = μ̂−2(μ12ρ1 + μ22ρ2 + ⋯    + μm2ρm). The excess thermodynamic properties of the mixture (relative to a pure hard sphere Percus-Yevick fluid) are shown to be those of the effective pure fluid. The dielectric constant of the mixture is also that of the effective pure fluid. The case of polar-nonpolar mixtures is considered by allowing one or more of the dipole moments to vanish. It is found that the potential of mean force and spatial distribution of the nonpolar molecules is independent of the magnitude of the dipoles while the anisotropic correlations between the polar molecules are independent of the presence of the nonpolar species.
Electronic spectroscopy and source of spin-orbit coupling in phenyl sulfides
Authors: Becker Ralph S. , Jordan Anthony D. , Kolc Jaroslav
Published: February 2004

Monoalkyl and diphenyl sulfides have a significantly higher value of the ratio φp/φF and shorter phosphorescent lifetimes than do the ether (oxygen) analogs. The results in the sulfides are explained in terms of the existence of: (1) a To,π* state between the lowest S1 (π, π*) and T1 (π, π*) states, (2) first-order spin-orbit coupling involving one-center terms connecting S1 and the Tσ,π* state and a heavy-atom effect, and (3) a relatively large second-order coupling (pertinent to the lifetime). The addition of HCl(g) to phenyl-n-propyl sulfide causes a dramatic change in the absorption and emission spectra, the value of φp/φF, and τp such that all of these become essentially identical to those of anisole. The latter results establish the importance of the role of the nonbonding electrons of sulfur in determining the spectral parameters of the sulfides and are consistent with the state energy ordering and the sources and nature of the couplings given above. Exciton interaction is a salient factor determining the differences in the φp/φF values of the diphenyl sulfides and ethers compared with the monophenyl derivatives.
Numerical extended-Hartree-Fock calculation of the magnetic hyperfine structure of lithium
Authors: Burke E. A. , Cassar L.
Published: February 2004

A two-determinant nonrelativistic approximation to the full extended-Hartree-Fock formulation is proposed. The approximation is tested on the ground state of the lithium atom. It is the intention of the authors to obtain calculated values of total energy and the hyperfine structure for lithium which are in reasonable agreement with comparable formulations. It is argued that the approximation is extendable and most attractive when applied to larger atomic systems. The two determinants are derivable from two spin functions [πi(αβ)i]σ and [πi(βα)i]σ where the products are over pairs of core orbitals and σ is the spin configuration of the valence orbitals. The one electron orbitals are determined numerically using an iterative self-consistent procedure. For lithium the electron spin density at the nucleus is calculated to be 2.8424/4π as compared to the value 2.9062/4π determined from experimental measurements of the magnetic hyperfine structure.
Ionization enhanced diffusion
Authors: Bourgoin J. C. , Corbett J. W. , Frisch H. L.
Published: February 2004

The diffusion equation and diffusion coefficient parametrization are established for the normal ionization-enhanced diffusion mechanism and the Bourgoin mechanism. These mechanisms can facilitate the diffusion of impurities and defects in semiconductors and insulators. The Bourgoin mechanism is athermal, i.e., it does not require thermal activation.
Molecular electron affinities from collisional ionization of cesium. II. SF6 and TeF6
Authors: Compton R. N. , Cooper C. D.
Published: February 2004

The relative cross sections for the production of mass selected negative ions resulting from collisions of Cs with SF6 and TeF6 have been studied as a function of the incident cesium atom energy from 0 to 40 eV. Electron affinities (E.A.) for SF6 and TeF6 are derived from accurate measurements of the threshold for ion-pair production with the results E.A. (SF6)=0.54−0.17+0.1 eV and E.A. (TeF6)=3.34−0.17+0.1 eV. Dissociative ionization studies resulted in E.A.(SF5) ≥ 2.8 ± 0.2 eV and D(SF6−−F)=1.05± 0.1 eV.
Reorientational and angular momentum correlation times in gaseous tetrafluoromethane at moderate densities
Authors: Campbell J. H. , Seymour S. J. , Jonas J.
Published: February 2004

NMR 19F spin-lattice relaxation times and Raman 435 cm−1 doubly degenerate [ν2(e)] vibrational-rotation band shapes have been measured in gaseous carbon tetrafluoride at 25 °C and densities of 9 to 120 amagat. NMR spin-lattice relaxation times have also been measured over the temperature range of −60 to 40 °C for the above densities. The Fourier transform analysis of the Raman band shapes has allowed us to calculate the reorientational correlation time τθ,2. Since spin rotation interactions provide the dominant relaxation mechanism for fluorine in CF4, then the angular momentum correlation time τJ is obtained directly from the 19F T1 relaxation times with the assumption that the anisotropy of the spin-rotation interaction tensor is small. A comparison of our experimental τθ,2 and τJ relationship agrees well with that predicted by the dilute gas limit of Gordon's J - and M -diffusion model as extended to classical spherical molecules by McClung.
Exciton-phonon interaction in crystalline phenanthrene
Authors: Tomioka Kenichi , Amimoto Hiroyuki , Tomotika Tosiro , Matsui Atsuo
Published: February 2004

The polarized optical absorption spectrum of the first exciton band (the first progression member of 1A1 exciton band) of crystalline phenanthrene has been measured in the temperature range 81 to 293 °K. The exciton-phonon interaction is discussed using Toyozawa's theory. The lower energy tail of the first exciton absorption band is confirmed to be expressed by Urbach's rule with the modified steepness parameter σ′a = 2.39 and σ′b = 2.35. The half-width of the first exciton band is also confirmed to change linearly with temperature. The value of the steepness parameter and the temperature dependence of the half-width provide experimental evidences that the exciton-phonon interaction in crystalline phenanthrene is weak. The degree of the interaction is compared with that in anthracene. The assignment of the shoulder absorption band located at the first exciton absorption tail is discussed.
Properties of two-component bimolecular and trimolecular chemical reaction systems
Authors: Tyson John J. , Light John C.
Published: February 2004

By a very simple argument we show that for chemical reaction mechanisms containing only bimolecular steps, which are open to a flow of matter so that there are only two time-dependent concentrations (X and Y), the steady state is either a saddle point, a center, or a stable node or focus. For mechanisms containing trimolecular steps we identify two processes which can lead to instability: A + 2X → 3X, and 2X + Y → 3X. The autocatalytic step A + 2X → 3X, where A is maintained at constant concentration, is explosive and it is very hard, if not impossible, to obtain limit cycle oscillations based on such an instability though we give an interesting example of conservative oscillations in a mechanism containing this step. There already exists a well-characterized mechanism admitting limit cycle oscillations which depend on the destabilizing self-limiting autocatalytic step 2X + Y → 3X, and these results suggest that this is the simplest example of chemical limit cycle oscillations. When the chemical reactions are coupled with diffusive processes, we also find that for bimolecular kinetics the nodes and foci are stable.
Correlation effects in atomic spin density distributions
Authors: Brown Richard Edwin , Larsson Sven
Published: February 2004

A comparison is made between the spin density distributions obtained from spin polarized Hartree-Fock (SPHF) and ``first order'' (FO) configuration interaction functions for atomic states with open 2s 2p shells. The SPHF spin densities are found to be close to those from the FO functions. Some additional comparisons are made with the extended Hartree-Fock methods.
Zeeman effect of 14N nuclear quadrupole resonance with polycrystalline samples
Authors: Pissanetzky Sergio
Published: February 2004

A theory of the Zeeman effect of 14N nuclear quadrupole resonance with polycrystalline samples is presented. A method for the identification of lines and the measurement of asymmetry parameters is described. The linewidth is taken into account and plays an important role. The results are general and apply for arbitrary angles between the radio-frequency magnetic field and the Zeeman magnetic field, and for any value for the asymmetry parameter between 0.005 and 0.993. No such results exist in the literature, since the only particular case reported so far is invalidated in its quantitative aspects by an error as demonstrated in this paper. The method is shown to be useful when only one line of a pair is known, when several lines have to be identified, or when attempts are made to assign the lines in ν+, ν− pairs. The results have been experimentally verified in several cases.
Microwave spectrum of cyclopropyl methyl ether
Authors: Penn R. E. , Boggs James E.
Published: February 2004

Microwave spectral assignments have been made for the ground and several excited vibrational states of a gauche rotamer of cyclopropyl methyl ether. For the ground state, the internal rotation splitting and intensity patterns are followed from the low K perturbed asymmetric rotor case to the high K pseudohindered symmetric rotor case, finding good agreement with theory for K values up to ∼ 16, above which the damping effect of the asymmetry is greater than calculated. The internal rotation splittings of the ground state transitions up to K ≈ 16 and the K = 0 → 1 Q branch transitions of the first excited methyl torsional state give a V3 barrier of 2276 ± 80 cal/mole. The dipole moment of 1.20 ± 0.02 D approximately bisects the COC angle.
Optical pumping of molecules II. Relaxation studies
Authors: Drullinger R. E. , Zare R. N.
Published: February 2004

The (ν″ = 3, J″ = 43) level of Na2 has been optically aligned using the 4880-Å line of a cw argon ion laser as a light source. The relaxation of this alignment is measured upon addition of foreign gas. In a low-pressure regime, where the mean free path exceeds the diameter of the light beam which both pumps and samples the alignment, the relaxation of the alignment versus pressure shows a ``dog-leg shape'' consisting of two linear regions. The first linear region corresponds to both elastic (velocity-changing) and inelastic (primarily rotational transfer) collisional relaxation whereas the second corresponds purely to inelastic collisional relaxation. The former process is dependent on the mode structure of the laser and shows saturation with increased pressure. In this low-pressure regime, the measured cross sections are shown to be lower bounds to the true cross sections and excitation by a multimode laser is shown to be inequivalent to excitation by a white light source when the width of the holes in the velocity distribution of the absorber molecules are nonoverlapping.
On the determination of spinodal temperature by electron microscopy
Authors: Sarkar A. , Gupta P. K. , Srinivasan G. R. , Volterra V. , Macedo P. B.
Published: February 2004

In a previous publication we reported that equilibrium composition fluctuations in the supercritical region of a multicomponent inorganic glass can be observed by replica electron microscopy and that the mean linear intercept length l(T, Xo) measured from the electron micrographs varies with temperature T according to a law of the type l(T, Xo) ∼ [T − To(Xo)]−ν; ν = 0.50. In the present paper we report measurements of the equilibrium volume fractions of the minor phase as a function of temperature and use them to estimate the spinodal temperature TSp(Xo). Our results suggest that TSp(Xo) = To(Xo); a result in agreement with the classical theories of phase separation.
Absorption line shapes and triplet exciton scattering times in organic crystals
Authors: Burland Donald M.
Published: February 2004

The low temperature singlet-triplet absorption line shapes of single crystals of naphthalene and 1,4-dibromonaphthalene are used to investigate the dynamic properties of triplet excitons. The line shapes although asymmetric, can be related to the approximate lifetimes of the k ≈ 0 exciton states. The temperature dependence of the line half-widths can be explained by acoustic phonon or lattice defect scattering at temperatures below 20°K. For 1,4-dibromonaphthalene an optical phonon mode begins to contribute to the line broadening above 20°K. The experimental linewidths indicate that exciton transport passes from an incoherent to a coherent process as the temperature decreases from 30 to 4°K.
Rotational band shapes in photoelectron spectroscopy: HF and DF
Authors: Walker T. E. H. , Dehmer P. M. , Berkowitz J.
Published: February 2004

Rotational line strengths for ionization are calculated assuming only s partial waves. Rotational band contours are then constructed by broadening each rotational line with a known instrumental line shape. This technique is applied to HF and DF, and reproduces the experimental results well, allowing an accurate value of the spin-orbit coupling constant to be extracted from experiment. The value of − 290 ± 10 cm−1 agrees with previous Hartree-Fock calculations. The ionization potentials (16.044 ± 0.003 eV for HF, 16.058 ± 0.003 eV for DF) are obtained with an accuracy one order of magnitude better than the experimental resolution, and there is some evidence for an electronic isotope shift.
Vibrational relaxation of hydrogen by direct detection of electronic and vibrational energy transfer with alkali metals
Authors: Jennings D. A. , Braun W. , Broida H. P.
Published: February 2004

A technique has been developed to measure the rate constant for vibrational relaxation of H2ν = 3,4 by H2ν = 0. The technique uses a mechanically chopped, tunable, cw dye laser coincident with either of the Na resonance lines at 589.6 or 589.0 nm. Sodium vapor is contained in a glass cell along with Cs atoms and H2. Sodium atoms, excited by the dye laser radiation, collisionally transfer electronic energy to H2 producing some H2ν. Only vibrational energy in H2ν from levels ν = 3,4 can transfer to Cs as electronic energy and cause Cs resonance line emission at 894 and 852 nm. In this manner, using the observed emission as a detector of H2ν = 3,4, the vibrational relaxation rate constant was determined to be 3.9 × 10−14 cm3 sec−1. Similar rate constants were measured, with somewhat less accuracy, for D2ν colliding with D2 and for H2ν colliding with He. It was found that N2, Na, and Cs also undergo electronic to vibration and vibration to electronic energy exchange.
Absorption and photoionization cross sections for H2O and D2O in the vacuum ultraviolet
Authors: Katayama D. H. , Huffman R. E. , O'Bryan C. L.
Published: February 2004

The total absorption, photoionization and neutral product cross sections for H2O and D2O have been determined over the wavelength range 580 to 1050 Å. The helium continuum was used as a background with a bandwidth of approximately 0.5 Å. Previously observed Rydberg series converging to the (000) level of the ionic ground state have been extended and utilized to obtain ionization thresholds of H2O (982.47 ± 0.5 Å, 12.619 ± 0.006 eV) and D2O (981.16 ± 0.5 Å, 12.636 ± 0.006 eV). At wavelengths shorter than 1000 Å, the total cross section curves for H2O and D2O exhibit a number of previously unreported bands superimposed on broad continua which have peaks at approximately 720 and 925 Å. These bands are most likely due to progressions belonging to Rydberg states converging to the first and second excited states of the molecular ion. There is evidence from photographic spectra of H2O16 and H2O18 that the Rydberg states converging to the first excited state of the ion (Ã2A1) have an effectively linear conformation.
Generalized scattering model for the hydrogen molecular ion
Authors: Pettifor D. G.
Published: February 2004

The importance of the nonspherical terms in Johnson's potential scattering treatment of molecules is illustrated for the particular case of the hydrogen molecular ion. These nonspherical terms lead in the angular momentum representation to a set of coupled differential equations, which can be solved analytically within the inscribed spheres. It is found that the wavefunctions are appreciably modified by these coupling terms, so that the generalized scattering model of Evans and Keller must be used if accurate eigenvalues are to be obtained. Analytic expressions for the s, p, and d components of the exact 1 σg and 1 σu eigenfunctions are derived within the inscribed spheres. The bonding eigenfunction does not display the contractive behavior predicted by the variational LCAO wavefunction.
Measurement of CO(ν = 1) vibrational energy transfer rates using a frequency-doubled CO2 laser
Authors: Green W. H. , Hancock J. K.
Published: February 2004

Laser-induced fluorescence studies of CO collisional relaxation have been carried out using the output of a frequency-doubled, pulsed CO2 laser as a direct source of CO(ν = 1) excitation. Energy transfer cross sections at 298 °K are reported for CO in collisions with He, Ar, H2, D2, N2, O2, Cl2, NO, CH4, CF4, and SF6. The D2–D2 self-relaxation rate was also obtained from the analysis of CO–D2 mixtures.
Studies on the lowest triplet state of mono- and dicarbonyl compounds. II
Authors: Gacoin P. , Leclercq J. M.
Published: February 2004

The modified CNDO method of Del Bene and Jaffé has been applied to the study of the phosphorescence spectra of some carbonyl compounds, namely, benzaldehyde, acetophenone, propiophenone, and various forms of the β-diketone studied in the first paper of this series: the keto form and two chelated enol forms of benzoylacetone. The results are quite satisfactory. The phosphorescence spectra of the carbonyl compounds and the keto form of benzoylacetone has been assigned to a n → π* transitions whereas the phosphorescence spectrum of the preponderant chelated enol form of benzoylacetone has been assigned to a π → π* transition.
Rate constants for the reaction of CH3 with N2F4 and NF2
Authors: Rice James K. , Truby Frank K.
Published: February 2004

The rate constants for the following reactions have been determined by mass spectrometric measurements following flash photolysis of CH3I/N2F4/(NF2)/N2 gas mixtures: CH3 + N2F4 → CH3NF2 + NF2, k1 = 6.7 ± 0.8 × 10−12 cc/molecule · sec (1), and CH3 + NF2(+M) → CH3NF2, k2 = 2.0 ± 1.1 × 10−12 cc/molecule · sec (2). The measurements were made near room temperature (40 °C) with sufficient N2 buffer gas to insure that only ground-state methyl radicals were reacting. Changes in the buffer-gas pressure did not change the observed second-order rate constant k2. This result is consistent with the rapid HF elimination from CH3NF2 that has been estimated for Reaction (2).
Dipole moment derivatives and vibrational intensities of BCl3
Authors: Bruns Roy E. , Kuznesof Paul M.
Published: February 2004

The CNDO approximate molecular wavefunctions for BCl3 have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates. New experimental derivatives calculated from previously published intensity data are presented. The set of experimental derivatives with respect to internal coordinates definitely preferred by these calculations is that with all signs negative. Inclusion of the d orbitals of chlorine in the atomic orbital basis set markedly influences the magnitudes of the derivatives as well as improves the agreement with the experimental in-plane and out-of-plane bending derivatives. The pd polarization terms appear to play an important role. Our results for BCl3 are compared with those previously obtained for BF3.
Relaxation processes in excited CO states. Part III: Inelastic cross-relaxation and radiative transitions caused by weak perturbations
Authors: Slanger T. G. , Black G.
Published: February 2004

An analysis has been carried out of the pathways by which low lying vibrational levels of the d3Δ and e3Σ−- states of CO are collisionally populated from higher levels produced by resonance absorption of CO resonance radiation. It has been established that a principal source of the d3Δν=3 and d3Δν=4 levels is energy transfer between ground state CO and an e3Σν=4− molecule. The experiments suggest that transfer of the entire electronic energy of the e3Σν=4− molecule occurs. The highly populated d3Δν=5 level is a less important source of the lower 3Δ levels than is e3Σν=4−. In the presence of several torr Ar, cross relaxation between the A1Π state and the triplet states becomes very important, and appears to take place elastically. For example, A1Πν=0 is a source of d3Δν=4, but not of d3Δν=3. Whereas earlier work had demonstrated that the strong spin-orbit perturbations of d3Δν=5 by A1Πν=1 caused the d3Δν=5 − X1Σ+ transition to be intense enough to observe resonance radiation effects, we have now shown that similar effects, although considerably weaker, may be observed with d3Δν=4 and d3Δν=3, where in the latter case the perturbing levels of A1Πν=0 lie 750 cm−1 higher. For the ν′ = 3, 4, and 5 bands of the d3Δ-X1Σ+ transition, the expected ratio of the CO absorption strengths can be calculated, based on the relevant A1Π-X1Σ+ Franck-Condon factors. The relative values are in reasonable agreement, and also agree with the data obtained for the A1Π ← X1Σ+ transition. Observations have been made on the e3Σ− → a3Π (1−ν″) bands, which have not previously been observed, and reason why transitions from the strongly perturbed e3Σν=1− level are not a more prominent feature in this system are discussed.
Semiclassical theory of molecular spectral line shapes in gases
Authors: Fitz D. E. , Marcus R. A.
Published: February 2004

A semiclassical theory of the width and shift of molecular spectral lines is developed for gases. Overlapping and nonoverlapping lines are considered, within the framework of the impact approximation. Use is made of ``exact'' semiclassical theory of molecular collisions, recently developed by Miller and by Marcus, and of developments in the quantum mechanical theory of spectral line shapes, by introducing the former into the latter. Comparison is made with a classical-like approach.
Paramagnetic contribution of magnetic shielding constant in some tetrahedral and octahedral molecules
Authors: Mohanty S.
Published: February 2004

Ground-state contributions to paramagnetic shielding constants of proton and fluorine nuclei in some tetrahedral and octahedral molecules have been obtained using Chan and Das's theory. The results are compared with observed values of molecular-beam experiments. Excellent agreement is obtained for proton shieldings. For fluorine shieldings, the method does not work well but gives values that are not as bad as the proton results reported earlier in some less symmetric molecules. A general trend of agreement is noticed with atomic number of the central atom (of all the molecules studied here) belonging to the same group of the Periodic Table.
Quenching of excited triplets of aromatic hydrocarbons by molecular oxygen
Authors: Benson Robert , Geacintov Nicholas E.
Published: February 2004

The quenching by molecular oxygen of photoexcited triplets of a number of aromatic hydrocarbons dissolved in a solid polystyrene matrix at 298°K was studied. The compounds studied are anthracene, pyrene, a, h-dibenzanthracene, chrysene, coronene, naphthalene, benz(a)anthracene, and eight of the latter's monomethyl derivatives. The quenching constant γ decreases with increasing triplet energy of the aromatic molecules and varies by a factor of seven, coronene yielding the smallest value and anthracene the highest. This result is in good agreement with the quenching studies in fluid solutions by Porter and co-workers and is due mainly to a decrease in the Franck-Condon factors with increasing triplet energy. Within the methyl benz(a)anthracene family, variations in the Franck-Condon factors are minor but differences in γ of up to 45% are observed depending on the position of the methyl group. With the methyl groups at the 7 or 12 positions of benz(a)anthracene, which are sites of high electron densities, the quenching constant is the smallest. These results are attributed to variations in the electronic matrix elements β coupling the initial and final states within the intermediate bimolecular complex. Relative values of β are calculated using INDO molecular orbital coefficients and are compared to the experimental results.
Effect of high pressures on molecular electronic spectra and electronic relaxation
Authors: Lin S. H.
Published: February 2004

The purpose of this paper has been to develop a theoretical model which can be used to deal with the effect of high pressure on the spectral band shapes and frequency shifts of molecular electronic spectra, rates of electronic relaxation, transformation of electronic structures, etc. We have shown that this model predicts that the pressure-induced frequency shifts of vibronic bands are the same for different vibronic bands, the pressure dependence of the frequency shifts is parabolic, the relation between the rate of nonradiative decays and external pressure is exponential, and the pressure effect on the rate of nonradiative decays and the pressure-induced frequency shift of the corresponding electronic transition are closely related.
Quantum mechanical tunneling in NMR: Effects of a potential barrier having sixfold symmetry on the spectrum of a methyl group
Authors: Cobb Thomas B. , Johnson Charles S.
Published: February 2004

The Apaydin and Clough model of quantum tunneling rotation for a methyl group in a threefold symmetric hindering potential has been extended to potentials having sixfold symmetry. The spectra predicted by this extension have been generated for representative single crystal and powder patterns and the results compared with those of the threefold model. It is shown how misinterpretation of spectra which appear to fit the threefold tunneling description is possible, but significant differences occur only in a very limited range of tunneling frequencies which correspond to rather unrealistically high sixfold barrier heights. Some experiments are suggested which could possibly lead to experimental verification of the predicted effects directly in the NMR spectrum.
Methods for experimentally determining the angular velocity relaxation in liquids
Authors: Kushick Joseph , Berne Bruce J.
Published: February 2004

It is shown that the angular velocity autocorrelation function for symmetric top molecules can in principle be determined from infrared and Raman band shapes, and from thermal neutron scattering when the molecular tumbling rate is slow compared with the relaxation of angular momentum. The theory is compared with molecular dynamics studies on a liquid crystal and an isotropic liquid.
Rayleigh scattering: Orientational motion in highly anisotropic liquids
Authors: Dardy H. D. , Volterra V. , Litovitz T. A.
Published: February 2004

Light scattering studies of the depolarized Rayleigh line are reported for liquid benzene over the temperature range +13 to 76°C and for other substituted benzenes. Values of the 〈 P2(o)P2(t)〉 and 〈 Ṗ2(o)Ṗ2(t)〉 correlation functions calculated from these spectra show considerable free rotor behavior (∼ 15° steps) and incomplete loss of memory after collision. Further consideration of the 〈 Ṗ2(o)Ṗ2(t)〉 correlation allows calculation of the angular velocity correlation function. The time between collisions, τBC, is also obtained and found to be in good agreement with a ``moveable wall'' cell model. It is proposed that the ``shoulder'' noted in the wings of many anisotropic liquids is caused by incomplete loss of memory after collision.
Effect of lattice vibrations on the NMR second moment. I. Intramolecular contribution
Authors: Shmueli U. , Polak M. , Sheinblatt M.
Published: February 2004

The effect of average librational motion of rigid molecules in the solid on the second moment of the NMR spectral line is investigated. The intramolecular contribution to the second moment is corrected for these motions by representing  in terms of the libration tensor employing the formalism put forward by Schomaker and Trueblood. It is possible, with the aid of the equations derived here, to evaluate the motional correction of the intramolecular contribution to the second moment, for both single crystal and powder samples, using the relevant crystallographic positional and thermal parameters of the molecule in question.
Theoretical studies of the interaction of MgF2 with rare gas atoms
Authors: Hayes Edward F. , Siu Albert K. Q. , Kisker David W.
Published: February 2004

Nonempirical self-consistent field wavefunctions have been used to obtain the dipole moment of MgF2 as a function of bond angle. These dipole moments have been used to determine the dipole-induced-dipole interaction between various rare gas atoms and MgF2 for several F–Mg–F bond angles. These calculations predict that the dipole-induced-dipole interaction between MgF2 and argon, krypton, or xenon is sufficient to distort MgF2 from a linear configuration. This suggests a plausible explanation for the difference between the geometry of MgF2 in the gas phase and in krypton matrices.
Absence of a host-crystal deuterium effect on the phosphorescence lifetime of naphthalene
Authors: Borkman R. F. , Tsivoglou S. , Von Dullen R.
Published: February 2004

Phosphorescence lifetimes have been measured for naphthalene and naphthalene-d 8 in benzene, benzene-d 6, benzophenone, and benzophenone-d 10 host crystals at temperatures from 4 to 275°K. Within experimental error, there is no evidence for an intermolecular host-crystal deuterium effect on the phosphorescence lifetime of naphthalene or naphthalene-d 8. At the higher temperatures studied the naphthalene phosphorescence is weakened and the lifetime is shortened, yet there is no evidence for nonexponential decay or delayed fluorescence.
Kinetics and mechanism of the reaction of hydrogen and deuterium atoms with benzene and benzene-d 6
Authors: Kim Poongzag , Lee J. H. , Bonanno R. J. , Timmons Richard B.
Published: February 2004

The kinetics of the gas phase reactions of H (and D) atoms with benzene were investigated using fast flow techniques. Specific rate constants were obtained using two separate systems, one with ESR detection to monitor the decrease in atomic reactants and the other with mass spectrometry to follow the change in benzene concentration. The results from these two systems are in essential agreement with one another when discussed in the light of the proposed reaction mechanisms. The mass spectrometric studies lead to a recommended specific rate constant of (5.7 ± 1.0) × 1010 cm3 mole−1 · sec−1 at 300°K for the H+C6H6 reaction. The activation energies for the D and H atom reactions with C6H6 are equal, within experimental error, with the value of 2.70 ± 0.20 kcal/mole reported. For reasons discussed in this paper, it is concluded that this activation energy refers to the addition of the atomic reactant to the benzene ring. Since isotopic exchange reactions have been observed in these systems, the over-all rate of the D+C6H6 reaction obtained from the ESR studies is higher than the rate obtained mass spectrometrically for the H + C6H6 reaction. Competitive experiments using C6H6/C6D6 mixtures in reactions with H and D atoms revealed the absence of any primary kinetic isotope effect on reaction rates. Thus the rate determining step does not involve hydrogen (or deuterium) atom abstraction from the benzene ring. From the products observed mass spectrometrically, it is clear that the reaction of hydrogen atoms with benzene is an over-all complex process and must include reactions leading to (a) isotopic exchange, (b) net addition to the benzene ring leading ultimately to cyclohexane formation, and (c) some cracking of the benzene ring with formation of C2H6 and CH4 as well as probable other low-molecular weight saturated molecules.
On non-RRKM unimolecular kinetics: Molecules in general, and CH3NC in particular
Authors: Bunker Don L. , Hase W. L.
Published: February 2004

Monte Carlo rate constants for model CH3NC isomerization, determined at 200, 100, and 70 kcal/mole, disagree with theoretical predictions. Also, three different approximate methods of generating initial conditions at 200 kcal lead to divergent results. The molecule does not appear to us to obey the random lifetime assumption of conventional unimolecular rate theory at any of these energies. A discussion is given of the systematics of this kind of effect, and comments are made on the relationship between our results and those obtained in the laboratory.
Naphthalene-d8 phosphorescence in pressure-perturbed media at 77 °K
Authors: Beardslee R. A. , Offen H. W.
Published: February 2004

The phosphorescence spectrum and triplet lifetime of naphthalene-d8 have been measured as a function of pressure (1 atm-35 kbar) at 77 °K in five matrices: poly(methylmethacrylate), EPA, perfluoromethylcyclohexane, pentane, and benzophenone. Compression of these matrices results in strong spectral broadening which is attributed to increased solvent inhomogeneity and enhanced coupling with the lattice. The pressure-induced shift in the triplet energy is sensitive to the detailed interactions of host molecules with the solute molecule, and provides qualitative attitudes about the various types of interactions responsible for solvent perturbations of electronic processes.
Use of biorthogonal orbitals in calculation by perturbation of molecular interactions
Authors: Gouyet J. F.
Published: February 2004

A Rayleigh-Schrödinger type of perturbation expansion, using a partition of the Hamiltonian into non-Hermitian parts, and biorthogonal orbitals, is developed to study excited molecular states. In particular an expansion of the molecular interactions is defined in which all intramolecular terms cancel exactly.
PMR spectra of the 4-alkylnitrobenzenes
Authors: Beistel D. W. , Chen H. E.
Published: February 2004

Evidence of first-order alkyl-ring proton coupling is reported for the 4-alkylnitrobenzenes. Typical coupling constants of 0.7 Hz and 0.3 Hz were found for α-alkyl coupling with the ortho and meta ring protons, respectively, when the alkyl function was methyl, ethyl, and isopropyl. No β-alkyl coupling with ring protons was observed for the ethyl, isopropyl, or t-butyl groups, suggesting that the magnitude of the coupling constant is vanishingly small.