bluuebunny/crossref_metadata_2025 huggingface dataset:
Trajectory studies of hot atom reactions. II. An unrestricted potential for CH5
Authors: Valencich Trina , Bunker Don L.
Published: February 2004

An approximate empirical potential energy hypersurface has been fitted to a combination of experimental results and molecular structural information, by means of a trajectory analysis, without the restrictions imposed in Part I. On the basis of this, predictions are made for the incident energy dependence of the reactive cross sections when the reactants are T+CH4, T+CD4, D+CH4, H+CD4, and H+CH4. The scattering properties and some aspects of the energy disposal in these reactions are also examined, and the most characteristic molecular dynamic features of the reactions are described.
Dissociation energy of chlorine monofluoride
Authors: Nordine P. C.
Published: February 2004

Measurements of the equilibrium constant for the gas phase reaction F+Cl2=ClF+Cl by a Cl-atom chemiluminescence technique yield ΔH°0= −3.27±0.24 kcal/mole. This result settles the existing uncertainty in the spectroscopic determination of D°0(ClF) in favor of the larger value, 60.35 kcal/mole.
Densitometric measurements of the rate of carbon dioxide dissociation in shock waves
Authors: Kiefer John H.
Published: February 2004

The dissociation of CO2 in mixtures with Kr has been studied behind incident shock waves over the temperature range 3600–6500°K. The rate of the primary dissociation reaction was determined using the initial rate, laser schlieren method of Breshears, Bird, and Kiefer [J. Chem. Phys. 55, 4017 (1971)]. These experiments showed no trace of the ``dip'' phenomenon observed in previous schlieren dissociation studies and an extrapolation procedure was used for the estimation of initial rate. Arrhenius parameters obtained for the second order rate coefficient of Kr–CO2 mixtures (CO2 has about twice the efficiency) are logA = 14.59 (A in cm3/mole · sec) and an activation energy Ea = 107.2±1 kcal/mole. Agreement of both the present dissociation rates and recent low-temperature measurements of recombination to either classical RRK or RRKM expressions is obtained with a threshold energy for dissociation of 130–132 kcal/mole.
Gaussian wavefunctions in a semicontinuum model for solvated electrons
Authors: Feng Da-Fei , Ebbing Darrell , Kevan Larry
Published: February 2004

Gaussian wavefunctions have been compared with previously used hydrogenic wavefunctions in a semicontinuum model for solvated electrons. Although the Gaussian function eliminates the physically unreal cusp associated with a hydrogenic function there is little significant difference in the total energies and optical transition energies calculated with the two functions. The most significant difference is that the fraction of charge density enclosed within a given radius is greater for Gaussian than for hydrogenic functions.
Delayed emission from an organic mixed crystal: Decay and rise characteristics of phosphorescence from a biphenyl guest-carbazole host mixed crystal
Authors: Misra T. N. , Mandal Krishnagopal
Published: February 2004

The decay and buildup characteristics of phosphorescence of biphenyl guest-carbazole host mixed crystal have been investigated in the temperature range 15–110°K. The phosphorescence decay and rise are nearly exponential in the temperature range investigated. It has been found that the phosphorescence rise time of biphenyl guest is less than its decay time. This difference between rise and decay time in the ``real'' mixed crystal arises from heterogeneous triplet-triplet annihilation involving a guest triplet and a defect triplet. The delayed fluorescence of annihilative origin has not, however, been observed owing to a very small fraction of the triplets involved in annihilation. The temperature dependence of the guest phosphorescence lifetime is an intermolecular process and is controlled by the thermally excited process T1D → T*1D → T1H → T1G. A kinetic scheme for guest-impurity heterogeneous triplet-triplet annihilation is discussed. The thermal energy gap obtained from various Arrhenius plots relevant to the kinetic scheme is in good agreement with the spectroscopic energy difference T1H − T1D.
X-ray zero-angle scattering cross section of water
Authors: Hendricks R. W. , Mardon P. G. , Shaffer L. B.
Published: February 2004

The absolute x-ray scattering cross section for water has been determined at small angles for specimen thicknesses in the range 0.5≤μt ≤6.2 at 20°C and in the temperature range 6 to 75°C for μt = 1.0. The data determined as a function of specimen thickness are in agreement with a new determination of second order multiple scattering. After correction for multiple scattering, the temperature dependent results are in good agreement with the zero-angle scattering cross section computed from fluctuation theory. This result precludes certain cluster models of the structure of liquid water.
Breakdown of local equilibrium in coupled relaxation processes: Translational nonequilibrium during vibrational relaxation
Authors: Keizer Joel
Published: February 2004

Coupled relaxation processes involving several variables are examined using the theory of Markov Processes. This leads naturally to a relaxation equation for one of the variables which has the form of a master equation, but involves time dependent transition probabilities. The equation agrees with usual theories based on local equilibrium and time independent transition probabilities when both the correlations between the variables and the distribution function of the suppressed variables reach their equilibrium form more rapidly than the variable of interest. In order to test the relevance of deviations from local equilibrium, a model which mimics many of the properties of the coupled relaxation of translation and vibration for V−T energy exchange in a thermal reservoir is proposed and solved. Using cross sections which are like those for energy transfer in diatomic molecules, it is shown that important nonequilibrium correlations persist on the transient time scale of the relaxation of the translational degrees of freedom. These correlations can be large when the preponderance of molecules are initially in the ground state and are the order of magnitude of the enhancement of vibrational relaxation times observed at low temperatures.
Configuration interaction procedure based on the calculation of perturbation theory natural orbitals: Applications to H2 and LiH
Authors: Siu Albert K. Q. , Hayes Edward F.
Published: February 2004

A configuration interaction method, based on the calculation of perturbation theory natural orbitals, is presented. The method offers an attractive alternative to commonly used procedures for obtaining truncated configuration interaction wavefunctions. Studies of H2 and LiH indicate that natural orbitals obtained using first order perturbation theory are nearly identical to those obtained by standard configuration interaction techniques.
Resonance Raman spectra of the nickel, cobalt, and copper chelates of mesoporphyrin IX dimethyl ester
Authors: Verma A. L. , Mendelsohn R. , Bernstein H. J.
Published: February 2004

Resonance Raman spectra have been obtained for the Ni, Co, and Cu chelates of mesoporphyrin IX dimethyl ester in solution using the tunable Rhodamine 6G dye and Ar+ lasers. Several bands show variation of intensity and depolarization ratio with exciting wavelength. Excitation profiles for some isolated bands peak at the maxima of the corresponding α electronic absorption bands. The variation of depolarization ratio for some anomalously polarized bands (ρl > 3/4) has been interpreted in terms of lowering of the symmetry of metalloporphyrins from D4h. The rigorous symmetry of these chelates is proposed as Cs because of the effect of peripheral substituents. A vibrational assignment is suggested for some of the metal sensitive modes.
Vacuum ultraviolet and photoelectron spectra of fluoroethanes
Authors: Sauvageau P. , Doucet J. , Gilbert R. , Sandorfy C.
Published: February 2004

The photoelectron and vacuum ultraviolet absorption spectra of ethylfluoride, 1,1-difluoroethane, 1,1,1-trifluoroethane, and hexafluoroethane have been measured up to 20 eV. The photoelectron spectra show that the highest filled orbital in the ground state is an orbital mainly populated in the C–C bond in the molecules containing two or more fluorine atoms; for ethane itself and for ethylfluoride a mainly C–H and a mainly C–C orbital are almost degenerate. The ultraviolet absorption spectra can be interpreted in terms of Rydberg bands, some of which are superimposed on the ionization continuum.
PES of high-temperature vapors. VI. 304 Å and 584 Å PES of Zn, Cd, and Hg halides and the electronegativity scale
Authors: Berkowitz J.
Published: February 2004

The He I and He I photoelectron spectra of Zn, Cd, and Hg halides (except fluorides) are presented. The inner metal d-like orbitals exhibit a larger chemical shift for Zn and Cd halides than for Hg halides. Analysis leads to a larger electronegativity for Hg than for Zn and Cd, contrary to a recently reported result, but in agreement with the thermochemical Pauling scale. The partial cross sections manifest dramatic photon energy dependence; the ionization cross section of the p-like orbitals decreases drastically, that of the d-like orbitals increases very significantly while the s-like orbitals slightly decrease between 21.2 and 40.8 eV.
Effect of pressure on hydrogen bonds on organic solids
Authors: Moon S. H. , Drickamer H. G.
Published: February 2004

The effect of pressure to 125 kbar has been measured on the O–H (or N–H) stretching frequency in a number of hydrogen bonding solids. Some data were also obtained on C–H stretching frequencies and on peak widths. For the hydrogen bonding peaks the initial shift is to lower energy. In a number of cases the direction reverses after shifts of 200–300 cm−1. The C–H frequencies increase in energy at all pressures. The results can be reproduced quite well by a simple model which adds a repulsion from the surroundings to Lippincott's model of an isolated H bond. The regularities observed among a number of substituted phenols are discussed in terms of substituent effects. The C–H bands broadened slightly with pressure while the bands involved in hydrogen bonding broadened substantially. These observations are discussed briefly in terms of a configuration coordinate model.
Collision complex model for spin forbidden reactions: Quenching of O(1D) by N2
Authors: Tully John C.
Published: February 2004

A collision complex model based on the RRKM theory of unimolecular decomposition is developed to describe spin-forbidden molecular collision processes. The model is applied to the quenching of O(1D) atoms by molecular nitrogen. The calculated rate constant (300°K) is 7 × 10−11 cm3 mol−1 · sec−1, in excellent agreement with experiment. An average of roughly 30% of the 1.98 eV exothermicity of this process is predicted to go into product vibration. This suggests, in contrast to previous studies, that collision with O(1D) is a very efficient mechanism for vibrational excitation of N2.
Low temperature magnetic susceptibilities and phase transitions in two linear Ni2+ salts: TMNC and TMNB
Authors: Dupas C. , Renard J-P.
Published: February 2004

We studied the magnetic susceptibilities parallel and perpendicular to the chain axis in TMNC in the temperatures ranges 20–13 K and 4.2–0.4 K. These experiments lead to TN=(1.195±0.005) K, J/kB=(1.09±0.10) K, D/kB=(2.10±0.46) K. Because of the ferromagnetic character of the intrachain exchange parameter, the dipolar interchain interaction is much more important in TMNC than in isostructural TMMC, as shown by our calculations. In TMNB, a transition to a 3-d antiferromagnetic ordered state was found at TN=(2.680±0.010) K.
Radiative and radiationless transition phenomena in 1,4-, 1,3-, and 1,2-diazanaphthalene vapors
Authors: McDonald J. R. , Brus L. E.
Published: February 2004

A pulsed, frequency doubled dye laser has been used to study time and wavelength resolved emission from low pressure quinoxaline, quinazoline, and cinnoline vapors. The S1, 1(n−π*) states of quinoxaline and quinazoline undergo statistical limit intersystem crossing, while the S2 (π−π*) states undergo S2−S1 and singlet-triplet intermediate strong coupling. Excitation into S2 yields a two-component ``fluorescence'' having an S1-type emission spectrum, and a longer component lifetime 102–103 longer than predicted by the S0−S2 f number. This anomalous emission is discussed principally in terms of a sequential decay theory of Tric and co-workers. Intermediate strong coupling appears to evolve into statistical limit coupling as a function of excitation energy. The 3B2 quinoxaline collision free phophorescence lifetime is within a factor of 2 of its value in condensed phases at low temperature. Thus the existance of rotational degrees of freedom in the gas does not significantly enhance the T1→S0 intersystem crossing rate, in disagreement with a recent theory. Cinnoline exhibits no detectable long-lived phosphorescence or intermediate strong coupling emission.
Electronic and vibrational spectra of Cr2O7−− ions in potassium halide matrices
Authors: Radhakrishna S. , Sharma B. D.
Published: February 2004

Optical and infrared spectra of dichromate ions in KCl, KBr, and KI matrices are reported. Optical spectra of Cr2O7−− consist of three absorption bands that are attributed to the electronic transitions A11(t16)→T21(t15t21); A11(t16)→E1(t15t21) or T21(t15t21); and A11(t16) →T21(t15e1) on the basis of molecular orbitals. Fine structure caused by coupled vibration-electronic transitions is observed in the A11(t16)→T21(t15e1) band. This fine structure further splits at low temperature (77°K) because of the symmetry lowering of the dichromate ion from Td to C3v. Infrared spectra show a number of lines. A model that assumes that the dichromate ion enters the lattice by replacing two halide ions with no charge compensating vacancy satisfactorily explains all the experimental results.
Pressure dependence of electronic relaxation: A stochastic model
Authors: Freed Karl F. , Heller Donald F.
Published: February 2004

We have constructed an exactly solvable stochastic model describing the pressure dependence of electronic relaxation processes in polyatomic molecules. From it closed-form algebraic expressions for time resolved emission intensities and quantum yields are extracted. Fundamental to this model are (1) a variation of the radiative and nonradiative decay rates of the electronic state with vibrational excitation within that state and (2) a ``step-ladder'' collisional dynamics scheme similar in nature to those investigated by Montroll and Shuler and applied to diatomic molecules. We describe how this model can be used to obtain estimates of the average variation of the radiative and nonradiative decay rates with excess vibrational energy as well as the average vibrational energy transferred per vibrationally inelastic collision and the rate for this energy transfer process. Furthermore, the model suggests physical situations in which ``nonexponential'' electronic relaxation can be expected to be observed.
Luminescence of calcium tungstate crystals
Authors: Treadaway Michael J. , Powell Richard C.
Published: February 2004

Fluorescence, excitation, and pulsed fluorescence measurements have been made on a single crystal of CaWO4 over a wide temperature range. The temperature dependences of the integrated fluorescence intensities and lifetimes were obtained for different excitation wavelengths. A sharp increase in the fluorescence lifetimes is observed below about 75°K and zero-phonon lines can be observed. These results are used to formulate a model for the tungstate luminescent center based on the WO42− ion in a crystal field of S4 symmetry. Energy migration and impurity trapping effects are also discussed.
New optical method for studying anisotropic diffusion in liquid crystals
Authors: Hakemi H. , Labes M. M.
Published: February 2004

A new approach to studying diffusion in liquid crystals is described in which the optically observable textural changes in a nematic phase caused by a cholesteric diffusant gives direct visualization of the concentration gradient. Utilizing either homeotropic of homogeneous alignments under different boundary conditions, and with and without an applied magnetic field, the parallel and perpendicular components of the diffusivity have been determined for a cholesteryl ester diffusing into N-(p -methoxybenzylidene)-p -n -butylaniline as a function of temperature. The diffusion coefficients in the isotropic phase can also be determined by annealing at a high temperature and quenching to room temperature, whereupon the cholesteric texture is again developed. Values of the diffusion coefficients and the activation energies of the diffusion process are discussed and compared to other available data.
Chemical potentials and related thermodynamics of liquid Na–Cs alloys
Authors: Ichikawa K. , Granstaff S. M. , Thompson J. C.
Published: February 2004

Data on the temperature and composition dependence of the chemical potential of Na in liquid Na–Cs alloys, obtained from an electrochemical cell, are reported. A variety of thermodynamic parameters are calculated. In particular the long-wavelength limit of the concentration correlation function is calculated and used to rule out the existence of Na2Cs. Rather, it is shown that there are long range fluctuations (as at a phase separation) in the vicinity of xNa = 0.80. This incipient phase separation must then be the cause of anomalies in acoustic and other properties reported in the Na-rich portion of the phase diagram.
Translational energy dependence of the reaction cross section for Rb + CH3I → RbI + CH3 from 0.12 to 1.6 eV (c.m.)
Authors: Litvak H. E. , Ureña A. González , Bernstein R. B.
Published: February 2004

A crossed molecular beam study of the reaction of Rb with methyl iodide has been carried out over a wide range of translational energy. At each of seven different incident relative velocities, the total product flux and thus the reaction cross section σR was determined by integration (over the laboratory spherical polar angles) of the in- and out-of-plane angular distributions of RbI. Over the available range of Ē (the mean translational energy in the center-of-mass system), σR is an essentially decreasing function of Ē. This behavior is somewhat similar to the post-maximum decline of σR(Ē) for the analogous K+CH3I reaction, but whereas σR for that reaction exhibited a sharp maximum at Ē≃0.18 eV, any such maximum for the Rb reaction must be presumed to occur below 0.12 eV.
Ion model and dipole polarizabilities in energy calculations. The dissociation energies of the rare-earth monoxides and the alkaline-earth monoxides and monosulfides
Authors: Guido M. , Gigli G.
Published: February 2004

The applicability of the polarized ion model to the gaseous rare-earth monoxides and to the highly electropositive alkaline-earth monoxides and monosulfides has been proved. The polarizability values here used for O−2, S−2, Ca+2, Sr+2, Ba+2, and rare-earth double ions indicate the possibility of establishing a polarizability scale to be used in ion model calculations.
Laser measurements of the radiative lifetime of the B2Σ+ state of CN
Authors: Jackson W. M.
Published: February 2004

A tunable dye laser has been used to measure the radiative lifetime of the individual rotational levels of the B2Σ+ state of CN. The radiative lifetime of the unperturbed rotational levels is 65.6±1.0 nsec, in agreement with previous workers. A longer radiative lifetime of 72±1 nsec is observed for the K′ = 4 level of the B state. The measured values of the perturbed and unperturbed levels support the longer lifetimes for the A2Π state of CN. The quenching cross section of the B2Σ state of CN is 41±20 Å2 and is independent of the rotational energy of the B state.
Laser photoluminescence spectroscopy of photodissociation fragments
Authors: Jackson W. M. , Cody R. J.
Published: February 2004

Laser induced photoluminescence spectroscopy has been used to study the energy partitioning among CN fragments produced by the photodissociation of C2N2. The CN radicals are produced in both the A2Π and the X2Σ+ states. The A state is formed primarily in the ν′ = 0 level, and the X state is formed in the lower vibrational levels. Since the photodissociation process does not produce the maximum amount of vibrational excitation in the CN fragments, it is suggested that the excess energy goes into either translational and/or rotational excitation of the CN.
Velocity dependence of absolute total cross sections for LiF scattered by nonpolar targets
Authors: Dehmer P. M. , Wharton L.
Published: February 2004

Total cross sections accurate to 1–2 percent were measured in the thermal energy range for LiF scattered by rare gas atoms (He, Ne, Xe) and nonpolar molecules (D2, CH4). In all cases, the cross sections were pressure independent, indicating that (1) the scattering was not a discernable function of the internal state of the primary beam molecule, and (2) the degree of inelasticity occuring at the outermost impact parameter regions probed was small. This allowed the observed velocity dependence of the cross sections to be interpreted in terms of spherically averaged monotonic potentials except in the cases of LiF–He, LiF–Ne, and LiF–D2 where the repulsive and well regions are probed. For every system, the slope d lnQ/d ln v of the cross section deviated from the theoretical slope of −0.4 predicted for a pure van der Waals 1/r6 interaction, suggesting the presence of higher order forces. As the size of the impact parameters explored increased, as increasingly large scattering targets were used, the slopes approached −0.4. For systems which sampled attractive regions of the intermolecular potential, cross sections which were calculated from the Schiff-Landau-Lifschitz (SLL) relation using the induction energy and the Slater-Kirkwood dispersion energy were 6–8 percent smaller than the corresponding experimental cross sections. For LiF–Xe, the system which most closely approached pure van der Waals behavior (with a slope of −0.389), the calculated cross section was 8 percent smaller than experiment. The absence of glory oscillations in the cross sections, attributed to rotational transitions at small impact parameters, provided an estimate of the lower limit for opacity at the glory impact parameter.
Generalized Langevin equation approach for atom/solid-surface scattering: Collinear atom/harmonic chain model
Authors: Adelman S. A. , Doll J. D.
Published: February 2004

Zwanzig's approach to inelastic atom/harmonic chain scattering is recast in a form which suggests generalization to atomic collisions with real solid surfaces. We reduce the infinite set of equations of motion for the impinging atom and harmonic chain to a pair of equations of motion. These equations describe the collision of the incident particle with a generalized Langevin oscillator. The first and second fluctuation-dissipation theorems for the Langevin oscillator are verified and their implications for the scattering process are discussed.
Some new energy formulas for atoms and molecules
Authors: Politzer Peter , Parr Robert G.
Published: February 2004

An exact formula for the nonrelativistic ground-state energy of an atom or molecule is derived: E=12 ∑ A ZA2(∂ φA∂ rA)rA=0−12 ∑ A ∫ Z′ZAA=0 Z′A2[∂∂Z′A(∂φA∂rA)rA=0]NdZ′A.

The function φA is defined for each nucleus A by φA = rA V/ZA, where ZA is the nuclear charge and V is the total electrostatic potential produced by the electrons and nuclei at a point rA measured from nucleus A. φA represents the screening of nucleus A by the electrons and other nuclei. The integration must be carried out over an isoelectronic path, the number of electrons being equal to the actual number N in the atom or molecule being considered. Equation (I) gives the molecular energy as a sum of atomiclike terms. It is shown that atomic energies can be calculated with remarkable accuracy with the equation E=37Z2(∂ φ / ∂ r)r=0, using Hartree-Fock values for (∂φ/∂r)r=0. Equation (II) is identical in form with a relationship in the Thomas-Fermi theory of atoms. These equations emphasize the dependence of atomic and molecular energies upon the electrostatic potentials at the nuclei. This is further discussed and illustrated. A semiempirical formula for the energy of an atom as a power series in Z1/3 is also presented.
On the product of surface tension and compressibility of liquids
Authors: Present R. D.
Published: February 2004

The surface tension γ is inversely proportional to the isothermal compressibility κ, and the product κγ near the triple point is equal to 0.32±0.15 Å for many liquids of dissilimar binding, including liquid metals, molten salts, organic liquids, aqueous solutions, and liquids of the common gases. A semiempirical derivation of this relation is given, in which we use Fowler's formula for γ and two formulas for κ: (1) the scaled-particle Percus-Yevick hard-sphere compressibility formula and (2) the compressibility derived from Carnahan and Starling's equation of state. We find that ρkTκ = 0.04±0.03 for many liquids of dissimilar binding, including the categories mentioned above (ρ = number density). Values of κγ obtained for liquid 4He and liquid 3He extrapolated to 0°K are found to agree with the κγ values of classical liquids.
Electron-impact excitation of the low-lying electronic states of formaldehyde
Authors: Chutjian Ara
Published: February 2004

Electron-impact excitation has been observed at incident electron energies of 10.1 and 20.1 eV to the first five excited electronic states of formaldehyde lying at and below the 1B2 state at 7.10 eV. These excitations include two new transitions in the energy-loss range 5.6–6.2 eV and 6.7–7.0 eV which have been detected for the first time, either through electron-impact excitation or photon absorption. The differential cross sections of these new excitations relative to that of the optically-allowed 1B2 ← X̃ 1A1 transition are given at scattering angles between 15° and 135°. These cross-section ratios peak at large scattering angles—a characteristic of triplet ← singlet excitations. From a comparison of the observed and calculated vertical transition energies, the transitions are assigned as 3A1 ← X̃ (5.6–6.2 eV) and 3B2 ← X̃ (6.7–7.0 eV). The design and performance of the electron-impact spectrometer used in the above observations is outlined and discussed.
Rotational lifetimes and self-quenching cross sections in the B 3Πou+ state of 127I2
Authors: Paisner J. A. , Wallenstein R.
Published: February 2004

Lifetimes and self-quenching cross sections of individual rotational levels in the B 3Πou+ state of 127I2 were measured by observing the fluorescent decay following excitation by an optical pulse from a narrowband tunable dye laser. The investigated levels were excited via 127I2 transitions coincident with Ar+ and Kr+ laser lines. The accurately determined rotational lifetimes and self-quenching cross sections are compared with those known for the same or adjacent vibrational states.
The methanium ion, CH5+. Evidence for the structure of a nonclassical ion from reaction studies by ion cyclotron resonance spectroscopy
Authors: Sefcik Michael D. , Henis Jay M. S. , Gaspar Peter P.
Published: February 2004

Studies of proton and deuteron transfer from methanium ions to various substrates and collision-induced dissociation of isotopically substituted methanium ions suggest that under the low-energy conditions of the ICR experiment, the addition of a hydrogen ion to methane produces a methanium ion whose hydrogens are structurally and chemically distinguishable. The reactions of methanium ions formed in the low energy electron impact ionization of CH4–CD4 mixtures are compatible with a methanium ion of Cs symmetry in which intramolecular rearrangement does not occur. Reaction studies on the methanium ions formed by the exoergic proton transfer from D3+ to methane indicate that rapid intramolecular rearrangements occur in these ions.
Vibrational spectra and ring puckering progressions in the C–H stretching region of trimethylene oxide and several deuterated analogs
Authors: Wieser H. , Danyluk M. , Kydd R. A. , Kiefer W. , Bernstein H. J.
Published: February 2004

The infrared (vapor, and solid at 15°K) and Raman (vapor and liquid) spectra in the region of 2700–3200 cm−1 are reported for three deuterated analogs of trimethylene oxide, viz. α-d2, β-d2, and α,α′-d4, and compared to the spectra of the normal compound. All principal infrared absorptions and Raman lines have been identified and assigned to vibrational modes of the α-CH2 and β-CH2 groups (six stretching fundamentals and three scissoring overtones). A number of band sequences are observed in the infrared and Raman spectra of the vapors. They are ascribed to combinations of various C–H stretching fundamentals and CH2 scissoring overtones with the ring puckering vibration and its overtones. The puckering separations in these vibrationally excited states in general do not differ greatly from the pure puckering differences.
Standing-wave modification of Regge trajectories and its application to atom-atom and ion-atom scattering at thermal energies
Authors: Tani Smio , Inokuti Mitio
Published: February 2004

We consider the global behavior of the phase shift δ(k, l) as a function of linear momentum k and angular momentum l. The loci of points at which δ(k, l) = π/2 (mod. π) represent essential features of an interaction potential. In a series of examples, we illustrate close relations of these loci to (1) the strength of the interaction potential, (2) the presence of glory undulation in the total cross section, (3) the orbiting effect due to penetration through the centrifugal barrier at low energies, and (4) the domain in which semiclassical approximations are valid. On certain theoretical grounds, one may consider this new method to be a standing-wave modification of the direct-channel Regge trajectory approach. An application to the He–Li+ scattering is also presented.
Collisional relaxation of electronically excited Pb; 6p2 (3P2) and (3P1)
Authors: Ewing J. J. , Trainor Daniel W. , Yatsiv S.
Published: February 2004

Time resolved measurements have been made of the room temperature decay of excited electronic states of Pb. The excited atoms were produced by photodecomposition of tetramethyl lead and the concentrations of the excited states were monitored by atomic resonance absorption. Quenching rate constants of the spin orbit states 3P2 and 3P1 were obtained for the collision partners Ar, Xe, H2, D2, N2, and O2. These results are discussed in terms of curve crossings, curve merging, chemical reaction, and E→V energy transfer processes. Comparison is made with the quenching rate constants for these states reported by Husain and Littler.
Heat pulse induced delayed phosphorescence and fluorescence in molecular crystals
Authors: Attia A. I. , Loo B. H. , Francis A. H.
Published: February 2004

Fast heat pulses are utilized to examine the dynamics of electronic relaxation processes in neat and chemically mixed crystals. The kinetics of triplet exciton and trap phosphorescence and singlet delayed fluorescence are discussed and the results of several experiments presented. Fast heat pulses are employed to determine the electronic relaxation time of long lived spin-states of chemical traps in mixed crystals. It is suggested that the technique of heat pulse modulation of delayed fluorescence, exciton phosphorescence, and trap phosphorescence may be generally useful for the exploration of electronic relaxation dynamics in molecular crystals.
Semiclassical collision theory. Multidimensional Bessel uniform approximation
Authors: Kreek H. , Ellis R. L. , Marcus R. A.
Published: February 2004

A multidimensional Bessel uniform approximation for the semiclassical S matrix is derived for the case of four real stationary phase points. A formula is also developed for the particular case when four stationary phase points may be considered to be well separated in pairs. The latter equation is then used in the treatment of two real and two complex stationary phase points.
Electron scattering from NO and N2O below 10 eV
Authors: Zecca A. , Lazzizzera I. , Krauss M. , Kuyatt C. E.
Published: February 2004

Total electron scattering cross sections for NO and N2O in the energy range 0–10 eV were obtained from exponential attenuation in a straight-line collision chamber without a confining magnetic field. Good agreement is obtained with previous measurements where available. For NO, cross sections have been obtained for the first time for resonance structure in the energy range 0–2.5 eV. There appear to be small, sharp resonances between the large resonances. For both NO and N2O the cross section is observed to increase rapidly at very low energies. Structure in the cross sections is interpreted in terms of electronic states of NO− and N2O−.
Molecular beam electric resonance analysis of inelastic collisions: Vibrational relaxation of LiF scattered by polyatomic molecules
Authors: Mariella R. P. , Herschbach D. R. , Klemperer W.
Published: February 2004

A thermal beam of LiF molecules at ∼1100°K is crossed by a target gas beam at temperatures ranging from 300–800°K and the LiF scattered at a laboratory angle of 20° is analyzed by electric resonance spectroscopy. The relative populations are measured for the lowest four vibrational states of LiF in the J = 1, MJ = 0 rotational state. With Ar, Xe, N2, O2, NO, CO, HF, HCl, or CO2 as the target beam, the vibrational populations of scattered LiF correspond to a Boltzmann distribution with the same vibrational temperature (within ±30°K) as the unscattered beam. With an H2O beam at ∼300°K, weak relaxation is observed. With target beams of SF6, NH3, ND3, or CHFCl2, marked vibrational relaxation is observed. Comparison with the concurrent elastic scattering gives rough lower bound estimates for the differential cross sections for inelastic scattering: ≳ 0.02 Å2/sr for H2O and NH3 at a center-of-mass scattering angle θ∼45° and ≳ 0.05 Å/sr for CHFCl2 and SF6 at θ∼25°. In each case, the vibrational distribution of the scattered LiF (elastic + inelastic) remains approximately Boltzmann. For the SF6 case, the LiF vibrational temperature varies with the target beam temperature: Tv(LiF)∼800°K with the SF6 at ∼300°K and Tv(LiF)∼950°K with SF6 at ∼500°K.
Optically detected zero field magnetic resonance studies of the photoexcited triplet states of chlorophyll a and b
Authors: Clarke Richard H. , Hofeldt Robert H.
Published: February 2004

The zero-field EPR transitions for the triplet states of chlorophyll a and chlorophyll b in n-octane solutions at 2°K have been observed by optical detection methods. Both triplet absorption detection of magnetic resonance and fluorescence-microwave double resonance techniques were used. Sharp-line (5–20 MHz) zero-field EPR spectra were recorded for both molecules. The rates of depopulation for the individual triplet state spin sublevels were determined by microwave-modulated fluorescence intensity measurements. These experiments show that the middle spin sublevel is the most active in triplet state intersystem crossing for both chlorophyll a and chlorophyll b.
Nature of the interaction forces associated with the concentration fluorescence quenching of Nd3+ in silicate glasses
Authors: Chrysochoos John
Published: February 2004

The nature of the concentration fluorescence quenching of Nd3+ in silicate glasses, which is associated with the reaction Nd3+ (4F3/2) + Nd3+ (4I9/2) → 2Nd3+ (4I15/2), has been reinvestigated by monitoring the fluorescence intensity of Nd3+ at 1060 nm as a function of time. The experimental decay curves were compared with theoretical ones, based upon dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The latter two interaction models appear to predominate in deexciting Nd3+. Their relative contributions depend upon the [Nd3+]. At higher [Nd3+], rare-earth ions having another Nd3+ ion as a nearest neighbor, namely ion ``pairs,'' may give rise to possible contribution of exchange interactions through a rapid electronic excitation energy migration from an excited Nd3+ ion to such pairs.
Comparison of quasiclassical trajectory and classical S-matrix treatments of collinear collisions of F and D2
Authors: Whitlock P. A. , Muckerman J. T.
Published: February 2004

The dynamics of collinear collisions of F with D2(n 1 a=0) have been studied using standard quasiclassical trajectory and classical S-matrix (semiclassical) techniques for collision energies ranging from 0.65 to 5.50 kcal mole−1 in the center-of-mass system. The results are compared to previous quantum mechanical calculations on the same potential energy surface. At most only three transitions (NR 0→0, R 0→3, and R 0→4) are ``classically allowed'' at any energy studied. Of these, the only transition for which the ``uniform semiclassical'' and quasiclassical results are significantly different is R 0→4. The predicted energy dependence of this transition is discussed in terms of recent experimental determinations of the relative rates of R 0→4 and R 0→3. The ``classically forbidden'' R 0→2 transition is predicted (using the complex-valued trajectory method) to have a probability which exhibits distinct oscillations as a function of collision energy.
Proton spin thermometry and molecular dynamics of the liquid crystal PAA in the solid phase
Authors: Thompson R. T. , Kydon D. W. , Pintar M. M.
Published: February 2004

The molecular motions in the solid phase of PAA from 77°K to the solid-nematic phase transition have been investigated using proton magnetic resonance and spin thermometry. This has shown that there are at least four dynamic processes that influence the relaxation times. Between 77 and 167 °K, the CH3 reorientation about the C3 axis is the predominate relaxation mechanism. In the region 167–238°K the rotation of the CH3 about the C–O axis and C3 axis influence the relaxation. There is also indication of proton cross relaxation to the nitrogen. In the higher temperature regions, the rotations of the molecules and diffusion are apparent in the relaxation.
Vibrational analysis using crystalline models: Vibrational spectra and potential constants for Cs2LiFe(CN)6
Authors: Jones L. H. , Swanson B. I. , Kubas G. J.
Published: February 2004

Single crystal Raman and infrared powder spectra have been observed for Cs2LiFe(CN)6, and for species Cs2LiFe(13CN)6 and Cs2LiFe(C15N)6 enriched to 94% 13C and 99% 15N, respectively. The infrared spectrum of the 6Li isotopically enriched species has also been observed. The above vibrational data have been used in a normal mode calculation including interionic interaction potential constants and lattice modes. While the overdetermined A1g and Eg symmetry blocks converge readily, the 6×6 F1u symmetry block is ill defined. A comparison of the potential constants obtained for Cs2LiFe(CN)6 with those obtained earlier for Co(CN)6−3 shows that the M–C sigma bonding is slightly weaker for the iron complex.
Electron drift mobility in 2-methyltetrahydrofuran organic glass
Authors: Huang Timothy , Kevan Larry
Published: February 2004

The electron drift mobility in 2-methyltetrahydrofuran glass has been measured by a time-of-flight method from 4.2 to 77 K and is 0.055 cm2 V−1·sec−1 at 77 K. The mobility is field independent from 16 to 40 kV cm−1. The mobility is approximately temperature independent from 4.2 to 36 K and increases exponentially with temperature above 36 K with an activation energy of ≈0.0035 eV. The Debye temperature of this matrix appears to be ≈35 K. Below 35 K incoherent hopping transport is postulated which is little affected by acoustical phonon modes. Above 35 K small polaron, hopping transport is postulated which is aided by excitation of optical phonon modes. The electron mobility in this organic glass is discussed with respect to electron mobilities in organic liquids and in aqueous glasses.
Magnetic properties of CsCl-type rare-earth cadmium compounds
Authors: Buschow K. H. J.
Published: February 2004

The magnetic and crystallographic properties of rare-earth cadmium compounds of equiatomic composition were studied. All compounds were found to be ferromagnetic. Indications were obtained that the CsCl structure type is not stable at all temperatures. The magnetic properties of the rare-earth cadmium compounds are compared with the isostructural zinc and magnesium compounds. It is suggested that, apart from the RKKY interaction involving s -conduction electrons, there exists a second coupling mechanism which in some cases even predominates.
Rotational diffusion model with a variable collision distribution. II. The effect of energy transfer
Authors: Frenkel D. , Wegdam G. H.
Published: February 2004

In this paper we present the results of model calculations on the rotational motion of linear molecules in dense systems. To this end we have developed a matrix description for the rotational diffusion, which is extended in this article to the J-diffusion limit. Closed expressions are obtained for the orientational, angular momentum, and rotational energy autocorrelation functions. The precise time dependence of these correlation functions is determined by the time distribution of collisions and the magnitude of energy and momentum transfer during a collision. A systematic analysis of the role of these two effects on the rotational relaxation is presented.
Calculations of potential energy surfaces in the complex plane. IV. Ab initio surfaces for H3+
Authors: Jaffe Richard L. , Morokuma Keiji , George Thomas F.
Published: February 2004

Ab initio LCAO-MO-CI calculations are reported for selected geometries of H3+ in the vicinity of the real-valued avoided intersection and complex intersection. The complex energy difference between the two lowest singlet surfaces is compared to the corresponding DIM values. In addition, the effect of polarization functions in the basis set is investigated and atomic orbital electron populations for the complex CI wavefunction are determined.
Semiempirical potentials for alkali-noble gas interactions
Authors: Kielkopf J. F.
Published: February 2004

A semiempirical calculation of alkali-noble gas interatomic potentials applicable to excited states of the alkali at internuclear separations and energies important for the interpretation of optical line broadening experiments is presented. The assignment of a single adjustable parameter is based on a comparison with scattering cross-section measurements of ground state potentials. Evidence that the repulsive interaction scales as the collision cross section of the noble gas atoms for low energy electrons is presented, and simple formulas are developed to predict potentials for all alkali-noble gas combinations as a function of noble gas dipole and quadrupole polarizabilities and alkali unperturbed energy. Additional comparisons are made with data from satellite bands in Cs–Xe and Cs–Kr spectra, and the impact broadening and shift of alkali spectral lines at low foreign gas pressure is calculated from the predicted potentials and compared with available experimental data.
Optical emission spectra produced by electron impact excitation of benzene
Authors: Smyth Kermit C. , Schiavone James A. , Freund Robert S.
Published: February 2004

Optical spectra excited by low energy electron impact on benzene show the characteristic fluorescence (S1→S0, 1B2u→1A1g) of the parent molecule. At energies above 50 eV this benzene emission becomes weak and fragment emission from H, C, CH, and C2 predominates. In addition, at high electron energy an underlying continuum (or possibly many, closely-spaced lines) is present throughout the 220–520 nm spectral region. This continuum is responsible for the broad peak at ∼150 eV in the previously reported excitation function for wavelengths corresponding to the benzene fluorescence. The emitter of the continuum radiation has not been identified.
Anisotropic intermolecular potentials from an analysis of spectra of H2- and D2-inert gas complexes
Authors: Le Roy Robert J. , Van Kranendonk J.
Published: February 2004

A method is developed for analyzing the discrete infrared absorption spectra of the van der Waals complexes formed between H2 or D2 and Xe, Kr, Ar, or Ne. Its application involves automatic nonlinear least squares fits of trial spectra calculated from realistic three-dimensional intermolecular potential models, to the experimental data. The secular determinant method used for calculating the energy levels of the anisotropic trial potentials proves to be highly reliable and relatively inexpensive. As a result, the present techniques should be readily applicable to cases where the anisotropic part of the potential is much stronger than it is here. The potential form used here is a Lennard-Jones (m, 6) function with independent long- and short-range anisotropy coefficients, and independent parameters characterizing the effect of the stretching of the hydrogen bond on the attractive and repulsive parts of the potential. The final fits concurrently used all uniquely assigned and nonoverlapping lines of both isotopes (H2 and D2) of a given complex, and all parameters (except ``m,'' which was varied manually) were allowed to vary simultaneously. The resulting potential surfaces are compared with those determined from molecular beam and relaxation time measurements.
Correlation of nuclear quadrupole resonance and 119mSn Mossbauer spectral parameters
Authors: Debye Nordulf W. G. , Linzer Melvin
Published: February 2004

A precise redetermination of the 119mSn Mössbauer spectral parameters of a large number of organotin (IV) halides and of the tin (IV) tetrahalides has been made. The 35Cl NQR resonance spectra of (CH3)3SnCl and of (n-C5H11)2SnCL2 have been measured for the first time. These data, in conjunction with literature values of other halogen frequencies in this series, yield correlations of both the central tin atom Mössbauer isomer shift and quadrupole splitting values with the reduced ligand NQR coupling constants. The correlations may be interpreted qualitatively in terms of the bonding trends expected on the basis of ligand electronegativities, and the uniformities of the correlations strongly indicate a lack of sharply defined structural variations within these compounds.
Photon yields and spectra resulting from reactions of Ca with oxidants
Authors: Capelle Gene A. , Jones C. R. , Zorskie J. , Broida H. P.
Published: February 2004

Calcium atoms have been reacted with various oxidants to produce chemiluminescence of CaO, CaBr, CaCl, and CaF. Spectra of the flames were recorded, and photon yields were measured for the reactions. Photon yields of CaO at 1.2 torr vary from 6.0×10−2 for Ca+O3 to 0.04×10−2 for Ca+NO2. Ca+F2 gives yields as high as 0.9×10−2, while Cl2 and Br2 are considerably less efficient as oxidants.
Crystal structure of bromomalonamide: Study of hydrogen bonding and thermal motions
Authors: Picone R. F. , Rogers Max T. , Neuman M.
Published: February 2004

The crystal structure of bromomalonamide, HBrC(CONH2)2, has been determined from MoKa diffractometer data by use of Patterson and Fourier syntheses. The crystals are orthorhombic, Pnma, with cell constants at 22°C: a =9.487(3) Å, b =11.294(4) Å, c =5.885(3) Å, ρc =1.90 g cm−3, pm = 1.85 g cm−3. The value of R1 for 270 observed reflections is 0.029. There are four molecules in the unit cell and one-half molecule in the asymmetric unit. The bond lengths are C–Br, 1.954(5) Å; C=O, 1.236(7) Å; C–N, 1.290(5) Å; and C–C, 1.522(9) Å. The three-dimensional hydrogen bonding network contains 8- and 12-membered rings with N ··· O distances of 2.94(1) and 2.82(1) Å, and H ··· O distances of 2.21(7) and 1.85(7) Å, respectively; the N–H ··· O angles are 164(7)°. A rigid body analysis of the thermal motions indicates that there is a librational motion, dominated by the hydrogen bonding scheme, of about 7° about a line joining the amide nitrogens of a molecule.