bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman and dielectric function spectra of strained GaAs1−xSbx layers on InP
Authors: Serries D. , Peter M. , Herres N. , Winkler K. , Wagner J.
Published: July 2002

Raman spectroscopy and variable angle spectroscopic ellipsometry (SE) were used to study pseudomorphically strained GaAs1−xSbx layers (0.22⩽x⩽0.65) grown on InP by metal-organic chemical vapor deposition. From the Raman spectra the composition dependence of the GaAs-like LO phonon mode was deduced. For comparison with literature data for unstrained GaAs1−xSbx, the strain-induced frequency shift of the GaAs-like LO phonon was calculated and subtracted from the present experimental data. When corrected for strain effects the composition dependent GaAs-like LO phonon frequency could be fitted by the linear relation ωLO=292.3−51x(cm−1) for the present range of alloy compositions. The pseudodielectric function spectra, deduced from SE measurements covering the range of photon energies from 0.8 to 5.0 eV, were fitted by a multilayer model employing a set of parametric oscillators to describe the GaAs1−xSbx dielectric function. From the resulting parametric dielectric functions the composition dependence of the E1 and E1+Δ1 critical point energies was deduced for pseudomorphically strained GaAs1−xSbx on InP and, after correction for strain effects on the interband transitions, also for unstrained GaAs1−xSbx.
Regular arrays of quantum-dot cellular automata “macrocells”
Authors: Pasky Jonathan R. , Henry Lisa , Tougaw P. Douglas
Published: July 2002

Previous research has shown the viability of fundamental quantum-dot cellular automata (QCA) structures such as binary wires, coplanar wire crossings, inverters, and programmable AND/OR gates. Combining these and other logic devices, we have designed and simulated a regular array of QCA “macrocells,” with each macrocell housing an irregular array of strategically aligned, identical arrangements of individual QCA cells. In the functional arrays presented, the outputs of successive columns of macrocells converge to a one-dimensional centroid of the initial region of binary inputs. With this precursor to fully developed cellular automata using QCA architecture, potential applications are destined in computer vision, robotics, and pattern recognition. A 10×10 regular array of macrocells is ultimately simulated, displaying the desired “centroidal convergence” behavior.
Optical and electrical properties of opal carbon replica and effect of pyrolysis
Authors: Kajii H. , Kawagishi Y. , Take H. , Yoshino K. , Zakhidov A. A. , Baughman R. H.
Published: July 2002

The optical reflection, electrical conductivity, and magnetoconductance of porous opal carbon replicas which have a periodic nanoscale structure have been studied. The temperature dependence of resistivity in green opal carbon replica is different from that in red opal carbon replica. The electrical properties of replica heat treated up to 3000 °C are consistent with those of pyrolitic graphite. The periodicity is found to decrease with this heat treatment by scanning electron microscopy and reflection measurements. Due to alkali metal doping, optical reflection spectra of replica with a heat treatment temperature of 2800 °C have changed drastically. The occurrence of positive magnetoconductance indicates the existence of quantum effect at low temperature. These results indicate that the electrical and optical properties can be controlled by pyrolysis technique and porous graphite can be obtained.
Anisotropic Seebeck and magneto-Seebeck coefficients of Bi and Bi0.92Sb0.08 alloy thin films
Authors: Cho Sunglae , Kim Yunki , DiVenere Antonio , Wong George K. L. , Ketterson John B. , Meyer Jerry R.
Published: July 2002

We have grown Bi and BiSb alloy thin films on (211)CdTe substrates by molecular beam epitaxy. Growth proceeds with the Bi or BiSb (00.1) axis oriented along the CdTe[111] direction, which is tilted by 19° with respect to the substrate normal. Measurements of the Seebeck coefficient reveal a strong dependence on angle within the plane, due to the anisotropic electronic structure. The coefficient measured along the [1̄11] axis, which includes a trigonal contribution from the Seebeck tensor, is considerably higher than the value along the [011̄] axis. The magneto-Seebeck coefficient was also studied, for magnetic fields of 0–0.7 T. We observe a strong dependence on both crystal-axis and magnetic field direction, the so-called “umkehr” effect.
Correlation functions from multiple solution of the transient Boltzmann equation in semiconductors: Application to noise temperature of holes in silicon
Authors: Hlou L. , Amechnoue K. , Diyadi J. , Vaissiere J. C. , Varani L. , Moatadid A.
Published: July 2002

We present a new numerical method to calculate the correlation functions in semiconductor materials by a direct solution of the Boltzmann equation. The correlation function is calculated solving a set of time-dependent Boltzmann equations corresponding to different initial conditions. As application, we present the calculation of the correlation function of velocity fluctuations and the noise temperature for holes in silicon at T=300 K. The results are in good agreement with Monte Carlo calculation as well as with experimental data.
Visible-near ultraviolet ellipsometric study of Zn1−xMgxSe and Zn1−xBexSe alloys
Authors: Lee Hosun , Kim In-Young , Powell J. , Aspnes D. E. , Lee S. , Peiris F. , Furdyna J. K.
Published: July 2002

We report pseudodielectric function data 〈ε〉=〈ε1〉+i〈ε2〉 of Zn1−xMgxSe and Zn1−xBexSe samples grown on GaAs substrates. The data were obtained from 1.5 to 6.0 eV using spectroscopic ellipsometry. Critical point parameters were obtained by fitting model line shapes to numerically calculated second energy derivatives of 〈ε〉, from which the bowing parameters and spin-orbit-splitting Δ1 of the E1 and E1+Δ1 gaps were obtained. A transfer of oscillator strength from E1+Δ1 to E1 with increasing Mg and Be composition and a positive bowing of these threshold energies are attributed to the k-linear interaction, which is large in small-band gap semiconductors.
Magnetic phase diagrams of the trilayers with the noncollinear coupling in the form of the proximity magnetism model
Authors: Yan Shi-shen , Grünberg P. , Mei Liang-mo
Published: July 2002

The magnetic phase diagrams of Fe/Mn/Fe trilayers with the noncollinear interlayer coupling in the form of the proximity magnetism model were theoretically studied. The C+–C− phase diagram in the remanent magnetization state predicts very rich spin configurations. The H–C+ and H–C− phase diagrams show that the spin configurations of Fe/Mn/Fe trilayers depend strongly on the external magnetic field, the anisotropy of Fe layers, and the coupling coefficients C+ and C−. Our experimental results of noncollinear spin configurations of Fe/Mn/Fe trilayers strongly support the magnetic phase diagrams based on the proximity magnetism model.
(
Mn
,
Sb) doped-Pb(Zr, Ti)O3 infrared detector arrays
Authors: Xu Y. Q. , Wu N. J. , Ignatiev A.
Published: July 2002

( Mn ,  Sb) doped Pb(Zr, Ti)O3 (PMSZT) thin film infrared (IR) detectors were integrated with Si substrates. The epitaxial PMSZT thin films, deposited on c-axis oriented YBa2Cu3O7−y (YBCO) bottom electrodes, show good ferroelectric properties with a remnant polarization Pr of 31 μC/cm2, a spontaneous polarization Ps of 38 μC/cm2, and a coercive field Ec of 21 kV/cm under an electric field of 76 kV/cm. Doping with Mn and Sb into Pb(Zr, Ti)O3 (PZT) not only decreased the Curie temperature TC from 350 °C for PZT to 175 °C for PMSZT, but also enhanced IR responsivity significantly. PMSZT thin films show high figures of merit, Fi of 15.5×10−9 C cm/J, Fv of 1758 cm2/C and Fd of 5×10−5 Pa−1/2 at 25 °C. IR detector arrays, fabricated with PMSZT films deposited on YBCO microbridges with an air gap between them and the substrate for reduced thermal mass, show a higher IR voltage responsivity compared to those without an air gap.
Picosecond excitation and selective intramolecular rates in supersonic molecular beams. IV. Alkylanthracenes
Authors: Syage J. A. , Felker P. M. , Semmes D. H. , Al Adel F. , Zewail A. H.
Published: July 2002

To assess the role of alkylation on IVR, the dynamics of jet cooled 9-methyl and 9-hexylanthracene excited to single vibronic levels (SVL) in S1 are investigated and compared with the parent molecule, anthracene, whose picosecond IVR dynamics are now well characterized. Vibrations in S1 and S0 are analyzed. Decay rates and SVL fluorescence spectra are also presented. The decay rates as a function of excess vibrational energy increase rapidly at low energy but become relatively constant at high energy. The approximate energy threshold at which the decay rate ‘‘saturates’’ is dependent on the substitutent; anthracene (≊1800 cm−1), 9-methylanthracene (≊1000 cm−1), 9-hexylanthracene (≊400 cm−1), and A–(CH2)3–φ (≤400 cm−1). These identified thresholds are discussed and related to IVR processes. Finally, some comments on the importance of low frequency modes to IVR are given.
KXe excimer absorption and S → D, S → F collision induced satellites in K–Xe mixtures
Authors: Johnson D. E. , Eden J. G.
Published: July 2002

The ultraviolet and visible absorption spectra of potassium vapor–xenon mixtures have been studied for [K] and [Xe] as large as 7×1017 and 4×1019 cm−3, respectively. Collision-induced absorption is observed in the ultraviolet (285≤λ≲370 nm) for the 4s → nf, nd (4≤n≤8) transitions but peak absorption lies an average of ∼0.6 nm to the red side of the position of the electric dipole forbidden line. The 4s → 4f, 5f transitions, in particular, are quite strong, having peak reduced absorption coefficients measured to be 1.1×10−39 and 2.6×10−40 cm5, respectively. Also, the KXe (C 2Σ) excimer has been observed in absorption for the first time. Absorption at the band peak (reduced absorption coefficient of ∼2×10−40 cm5 at λ=507 nm) is roughly two orders of magnitude weaker than that for the analogous bands of CsXe and RbXe and is displaced at least 5 nm to the blue side of the peak (∼520 nm) in the emission spectrum. Six reproducible undulations to the blue side of the absorption maximum display a periodicity of 111±17 cm−1.
Infrared multiphoton dissociation of methyl nitrite in a molecular beam: Internal states of the nitric oxide fragment
Authors: King David S. , Stephenson John C.
Published: July 2002

The rotational-, spin-, and lambda doublet-state distributions for nitric oxide (NO) formed in the CO2 laser multiphoton dissociation of methyl nitrite, CH3ONO, in a pulsed molecular beam are reported. Upon methyl nitrite photolysis by temporal square wave infrared laser pulses at 983 cm−1 of 50 ns duration and 800 MW/cm2 intensity, the low-lying rotational levels of the nitric oxide fragments formed in the 2Π1/2 (F1) and 2Π3/2 (F2) spin-orbit states exhibited Boltzmann-like population distributions, characterizable by the rotational temperatures TR (F1)=400±10 K and TR (F2)=530±100 K; the integrated populations for J<30.5 of the two spin components were in the ratio F1/F2=2.7 : 1. For those highly rotationally excited levels with J≳24.5 there is no measurable spin preference, the level population depending solely on total internal energy Eint. There is no apparent preference for formation of either lambda doublet component and there is no observable fragment alignment, the nascent NO species exhibiting an isotropic distribution of angular momentum vectors.
State-specific rates of H2CO(S)→H2+CO at energies near the top of barrier: A violation of RRKM theory?
Authors: Dai Hai-Lung , Field R. W. , Kinsey James L.
Published: July 2002

Unimolecular dissociation rates have been determined for two rovibrational eigenstates in the H2CO X̃ 1A1 electronic ground state. The two levels investigated are separated in energy by ∼30 cm−1 at a total energy near 28 300 cm−1, which is near the top of the barrier for dissociation to H2+CO. The angular momentum is J=2 for both levels, and they have the same vibration-rotation symmetry. Contrary to the expectations from conventional RRKM theory, the state higher in energy has a dissociation rate ∼2.5 times slower than the less energetic state.
Adsorption of polymer chains at surfaces. II. Amplitude ratios for end-to-end distance distribution at the critical point of adsorption
Authors: Eisenriegler E.
Published: July 2002

Previous work on polymer adsorption at surfaces is extended by evaluating universal amplitudes for a single chain, fixed with one end at the surface (called a ‘‘surface chain’’), at the critical point of adsorption. Ratios of mean square end-to-end distances of surface and bulk chains as well as short distance amplitudes for the end-to-end distance distributions of a surface chain are calculated. Contrary to a previous claim, the behavior of all these quantities is consistent with an effectively attractive surface at the critical point of adsorption.
The derivation of the rotational potential function from atom–atom potentials. I. Ammonium–chlorine compounds
Authors: Smith David
Published: July 2002

The rotational potential function of the ammonium ion in the ammonium hexachlorides and the disordered phases of NH4Cl and α-NH4HgCl3 are derived from atom–atom potentials of the Buckingham (exp-6) type. The parameters in the atom–atom potentials are determined by matching computed and observed values of the librational and tunneling frequencies of NH4Cl, (NH4)2SnCl6, and (NH4)2PdCl6. The procedure presented in this paper is particularly useful in the determination of the potential function of noncubic ammonium compounds, where there are a large number of parameters in the potential function. The volume dependence of the parameters in the potential function is easily computed when atom–atom potentials are used to derive the rotational potential function.
Multiple quantum jumps in vibrational energy transfer of iodine in the B 3Πu+ state along a supersonic beam expansion
Authors: Baba Hiroshi , Sakurai Katsumi
Published: July 2002

An argon ion laser (514.5 nm) excites the I2 molecules to B 3Π0u+ (v′=43) state at a certain point in the supersonic He and H2 jet, and the fluorescence spectrum is observed downstream. An extremely large vibrational energy relaxation of electronically excited iodine molecules in the expanding supersonic beam has been observed over the levels of Δv=−10–2. The vibrational population distribution along the jet flow was analyzed with the rate equation. The Δv dependence of rate constant in a single collision, kv→v+Δv, is assumed to be a simple function as k1→0 α|Δv|−1v(v−1) . . . (v +Δv+1), for Δv<0 and k1→0 α|Δv|−1 v(v+1) . . . (v +Δv−1) exp (−ΔE/kBTeff), for Δv>0, where ΔE is the energy gain by vibrational activation, Teff is the effective temperature and α is the fitting parameter for multiple quantum jumps, and K1→0, α and Teff have been determined to be 1.70±0.05×10−12(cm3/mol s), 0.0065 and 19 K, 3.2±0.1×10−12(cm3/mol s), 0.009 and 30 K for He and H2, respectively. It was found that vibrational multiple quantum jumps in a single collision contributed to the relaxation process and the relaxation rate constant seemed to be almost constant along the expanding flow.
Photodissociation dynamics of CO3−
Authors: Hunton D. E. , Hofmann M. , Lindeman T. G. , Castleman A. W.
Published: July 2002

The dynamics of CO3− photodissociation is studied with a new photodissociation spectrometer that allows kinetic energy-resolved detection of parent ions and photofragments. Kinetic energy release distributions, photodissociation spectra, and the dependence of the photofragment intensity on the laser power and background pressure are presented. Photodissociation of CO3− in the energy range 1.95–2.2 eV leads to CO2+O− fragments, and is found to occur by two distinct mechanisms. These mechanisms involve three electronic states that correlate with CO2+O−—the 2B1 ground state, a 2A1 weakly bound state, and a repulsive 2B2 state. The first mechanism begins with a low cross section 2A1 ← 2B1 transition that gives structure to the spectra. From this intermediate state, a second photon carries the ion to the 2B2 state. Dissociation to the observed photofragments occurs rapidly on the repulsive surface. In this two photon mechanism, at least 20% of the available energy is disposed of in relative translation of photofragments. The second mechanism is also initiated by the 2A1 ← 2B1 transition. Deexcitation of the 2A1 bound state by internal conversion, however, leads to high lying vibrational levels of the ground 2B1 state. These vibrational levels are found to have an enhanced collision-induced dissociation cross section.
Resonance Raman and fluorescence spectra of 1.8 dihydroxyanthraquinone in n-alkanes at low temperature. Evidence for excited state proton transfer
Authors: Smulevich G.
Published: July 2002

The resonance Raman and fluorescence spectra of 1.8 dihydroxyanthraquinone in n-hexane and n-heptane at 8 K have been measured. By using various exciting lines of an Ar+ laser, well resolved site selection spectra were obtained and evidence was found for the existence of at least two emitting excited states. The detailed analysis of the higher energy transition permitted identification of the totally symmetric vibrational modes and evaluation of the displacement of the minima of the potential surfaces of the ground and the dipole allowed excited states. The lower energy transition was interpreted in terms of an excited state relaxation mechanism involving proton transfer.
Conformational kinetics of methyl nitrite. III. Collisional energy transfer in the bimolecular region
Authors: Chauvel J. Paul , Friedman B. Ri. , Van Hoa , Winegar Eric D. , True Nancy S.
Published: July 2002

Bimolecular region unimolecular rate constants for the syn=anti conformed exchange in gaseous methyl nitrite and in methyl nitrite–bath gas (bath gases being He, Ne, Ar, H2, N2, O2, CO, CO2, NH3, SF6, CH4, C2H6, C3H8, n-C4H10, and n-C5H12) were obtained from line shape analysis of 200 MHz 1H NMR spectra. The pressure dependent rate constants were analyzed to yield relative bimolecular collisional activation efficiencies βMp on a pressure per pressure basis for each bath gas. The resulting βMp indicate that, for methyl nitrite conformational interconversion, which occurs at a low threshold energy, E0=11.70 (0.40) kcal/mol, and a low vibrational state density ρ(E0)=160 states/cm−1 intermolecular collisional energy transfer is dominated by the attractive portion of the intermolecular potential, with the energy transfer in the collisional complex being statistical. Corrections to previously published data are given.
A
b i
n
i
t
i
o multireference CI determinations of the electron affinity of carbon and oxygen
Authors: Feller David , Davidson Ernest R.
Published: July 2002

In order to better understand the requirements for obtaining ab initio electron affinities which agree with experiment to within 0.1–0.2 eV, a systematic study has been made of the effects of variations in basis set and choice of CI reference space configurations. Using balanced [8s, 5p, 4d, 2f, 1g] contracted Gaussian basis sets it was possible to obtain values of 1.22 eV for carbon (experimental=1.27 eV) and 1.29 eV for oxygen (experimental=1.46 eV). Enlargement of the (s,p) portion of the basis to near Hartree–Fock limit quality resulted in substantially more correlation energy being recovered but no significant change in the computed electron affinities.
The shape of two-dimensional polymers
Authors: Bishop Marvin , Michels J. P. J.
Published: July 2002

The shapes of two-dimensional linear and ring polymers, with and without excluded volume, are investigated by determining the ratios of the two principal orthogonal components of the mean-square radius of gyration. It is found that ring chains are more symmetrical than linear ones.
An effective core potential study of the mono- and tetracarbonyls of Ni, Pd, and Pt
Authors: Rohlfing Celeste McMichael , Hay P. Jeffrey
Published: July 2002

Effective core potentials (ECP’s) are used to determine SCF equilibrium geometries and properties of the mono- and tetracarbonyls of nickel, palladium, and platinum. For Pd and Pt, potentials including relativistic effects are employed. Electron correlation effects on metal–carbon and carbon–oxygen bond lengths are evaluated by second-order Møller–Plesset perturbation theory (MP2). Inclusion of correlation enhances π backbonding. For linear MCO, the 1∑+ state lies below the 3Δ state. Agreement with all-electron calculations and experiment is satisfactory. The predicted relative stability based on metal–carbonyl bond energies of both MCO and M(CO)4 is in the order Ni>Pt>Pd, as observed experimentally.
A method for systematic inclusion of electron correlation in density functionals
Authors: Harris R. A. , Pratt Lawrence R.
Published: July 2002

This paper outlines a program for the systematic treatment of correlation effects within density functional approaches to many-electron systems. This strategy is motivated by the observation that the ground state energy of an inhomogeneous electron gas is a functional of the many-body Hartree electron density. This fact is proved, and it is outlined how the functional can be constructed at any order of perturbation theory. Second order correlation contributions to the energy are discussed as an explicit example.
Universal curves of the thermodynamic properties of multichain lattice systems via extrapolation of computer experiment data to the scaling limit
Authors: Okamoto Hiroshi
Published: July 2002

According to the recent polymer theories, the thermodynamic properties of polymer solutions in a good solvent, at the scaling limit, are governed by a scaling variable composed of the polymerization degree n, the concentration φ, and the polymer dimension exponent ν. Our computer experiments on multichain lattice systems with the nearest-neighbor interaction afford us the configurational free energy or the osmotic pressure. The nearest-neighbor interaction or the solvent condition where the free energy best obeys the scaling is reinterpreted as the fixed point solvent condition in a lattice space RG context. We approach the scaling limit by extrapolating the data obtained at that solvent condition to the limit n → ∞. The osmotic pressure obtained by the procedure shows an excellent agreement with Ohta and Oono’s theory. The nonextrapolated chain dimensions at that solvent condition are also in a good agreement with the theory. It is found that a weak nearest-neighbor attractive interaction works between the chain elements at that solvent condition. We, therefore, should take care for saying about the scaling from experiments on athermal solutions. Many of our data appear to be successfully interpreted in terms of the RG context by the help of some optimistic expectation for the convergence.
Memory function for a colloidal liquid
Authors: Taylor Thomas W. , Ackerson Bruce J.
Published: July 2002

The reduced memory function has been measured for a dilute suspension of interacting colloidal particles as the ionic strength of the suspension was slowly decreased. Care was taken to minimize the effects of multiple scattering. In contrast to earlier measurements of Gruner and Lehman, the reduced memory function was found to increase in value with decreasing ionic strength over the experimentally accessible range of k space. The reduced memory function did not exhibit a universal character as the interaction between particles was increased, even to the point where the colloidal liquid was coexisting with the colloidal solid phase. Other features of the reduced memory function are also compared and contrasted with earlier measurements and theoretical models.
Phase diagram and correlations of fluids with very steep attractive forces
Authors: Tau M. , Reatto L.
Published: July 2002

The mean spherical approximation (MSA) is found inadequate in the presence of attraction between particles which is strong and of short range compared with the hard core diameter. This is a situation prevalent in applications of liquid state theory to micellar solutions and microemulsions. A generalized MSA is also studied in which conditions of thermodynamic consistency are implemented. The critical point is determined as function of the range of the attractive forces. We also discuss how the inadequacy of MSA affects the effective pair interaction deduced from experimental data for the structure factor.
Analytic energy derivative methods for excited singlet states of the same symmetry as the electronic ground state
Authors: Fitzgerald George , Schaefer Henry F.
Published: July 2002

The possibility of variational collapse of single configuration self-consistent field (SCF) wave functions for excited electronic states becomes more serious when first and second derivatives of the energy (with respect to nuclear coordinates) are required. For a nonlinear molecule of four or more nuclei, there will almost inevitably be some displacement which removes all spatial symmetry, leaving the electronic state in question with the same spatial symmetry as the ground electronic state. For excited singlet states, a resolution of this problem is found by using the Davidson–Stenkamp method to guarantee orthogonality to the closed-shell ground-state wave function. The Davidson–Stenkamp wave function is then transformed to a conventional two-configuration SCF wave function, to which analytic first and second derivative methods may be applied.
The treatment of triple excitations within the coupled cluster description of molecular electronic structure
Authors: Hoffmann Mark R. , Schaefer Henry F.
Published: July 2002

Equations for the determination of the cluster coefficients in a full coupled cluster theory involving single, double, and triple cluster operators with respect to an independent particle reference, expressible as a single determinant of spin-orbitals, are derived. The resulting wave operator is full, or untruncated, consistent with the choice of cluster operator truncation and the requirements of the connected cluster theorem. A time-independent diagrammatic approach, based on second quantization and the Wick theorem, is employed. Final equations are presented that avoid the construction of rank three intermediary tensors. The model is seen to be computationally viable, size-extensive, high-level description of electron correlation in small polyatomic molecules.
Computer simulation of the dynamics of trifunctional and tetrafunctional end-linked random elastic networks
Authors: Neuburger N. A. , Eichinger B. E.
Published: July 2002

Computer simulations of networks formed from telechelic polydimethylsiloxane with tri- and tetrafunctional crosslinkers are used to investigate the dynamical behavior of elastomers, especially in the long-time domain. The effective force constant matrices for these systems are determined by the topology of the networks that are formed; diagonalization yields relaxation time spectra. It is shown that there are modes of motion in elastomers that relax much more slowly than do dangling ends, and that these slow moving network modes are responsible for the plateau modulus. The longest relaxation time τmax is found to be proportional to N0.34v, where Nv is the number of junctions and chain ends in the network. The lower the extent of reaction, i.e., the closer the system is to the gel point, the greater is the contribution from slow modes. Network collapse remains a problem, since 〈s2〉0/〈l2〉0 is independent of network size even though it depends upon the extent of reaction.
Inversion barriers in NF+ 3̇ and CF ⋅ 3
Authors: Dixon David A.
Published: July 2002

The inversion barriers of NF+ 3̇ and CF ⋅ 3 have been calculated using ab initio molecular orbital theory. Geometries were optimized with a polarized double zeta basis set. The final inversion barriers were calculated with a near Hartree–Fock basis set of the form [10,6,4/5,3,2]. The inversion barriers are 12.3 kcal/mol for NF+ 3̇ and 35.2 kcal/mol for CF ⋅ 3. Estimates of correlation corrections from FO-CI calculations suggest that these are upper limits to the barrier heights. There is a clear discrepancy between the calculated value and an experimental estimate for NF+ 3̇.
Boron atom reactions with the halomethanes
Authors: Tabacco M. B. , Stanton C. T. , Sardella D. J. , Davidovits P.
Published: July 2002

Rate constants have been measured for the reactions of boron atoms with a series of halomethanes. The experiments were performed in a linear flow tube apparatus at 300 K. The measured rate constants in units of cm3 molecule−1 s−1 are CCl4:9.5×10−11; CCl3H:4.8×10−11; CCl2H2:6.2×10−11; CClH3:1.4×10−11; CCl3F:3.1×10−11; CCl2F2:5.5×10−12; CClF3:1.7×10−13; CF4:<3×10−14; CF3H:<2×10−14. The reaction of boron with all the chloromethanes is facile. The chlorofluoromethanes present a more complex pattern. Noteworthy is the low reactivity of the channel to produce BF, furthermore, the presence of fluorine in the halomethanes reduces the reactivity at the chlorine site. Semiempirical MNDO calculations were performed on the reacting systems. These calculations suggest possible explanations for the observed results.
ArF laser flash photolysis of hexafluorobenzene vapor: Formation of hot molecules and their collisional relaxation
Authors: Ichimura Teijiro , Mori Yuji , Nakashima Nobuaki , Yoshihara Keitaro
Published: July 2002

Time-resolved absorption spectra of hexafluorobenzene vapor have been observed in the time range of 0–2 μs after pulsed ArF laser (193 nm) excitation. The absorption spectrum observed at the time t=0 is attributed to HFB* (S0) (hot hexafluorobenzene with an internal energy of 639 kJ/mol). This transient absorption spectrum can be simulated as a part of the spectrum of the S3(1E1u)←S0 transition at 3050 K on the basis of a modified Sulzer–Wieland model. The collisional deactivation of HFB* molecules is explained in terms of an energy transfer model which assumes that the energy removed per collision depends upon the internal energy.
A variation-perturbation method for atomic and molecular interactions. I. Theory
Authors: Gallup G. A. , Gerratt J.
Published: July 2002

We have developed a variation-perturbation procedure for calculating intermolecular forces. It is based on the valence bond method of constructing wave functions and involves a number of interlocking techniques and approximations that are justified by the small size of the interaction potential relative to the total energy. In this article we give an outline of the theory of our technique. We have used this procedure to determine the potential between a Ne atom and a rigid HF molecule. The results of this calculation are given in the next article.
Exact classical calculations of vibrational energy transfer in a Morse oscillator
Authors: Ree Taikyue , Shin H. K.
Published: July 2002

Exact energy transfer in the collinear collision of a Morse oscillator with a particle is calculated from the numerical integration of the classical equations of motion over a wide range of collision energies. The exact classical energy transfer values are compared with those of the harmonic oscillator case for several different types of collisions. Except for the collisions involving a heavy homonuclear diatomic molecule and a light incident particle, the Morse energy transfer values are seriously different from the harmonic case. The time dependence of energy transfer during the collision especially at high collision energies is studied in detail to obtain information on the occurrence of multiple impacts in each collision. The deviation of the harmonic energy transfer from the Morse values is discussed in terms of the impact multiplicity.
The infrared absorption intensities of the water molecule: A quantum chemical study
Authors: Swanton David J. , Bacskay George B. , Hush Noel S.
Published: July 2002

Using ab initio Hartree–Fock SCF, configuration interaction, and approximate coupled pair techniques, an extensive quantum chemical study of the infrared absorption intensities of the water molecule is reported. In an attempt to establish the necessary requirements for the quantitative prediction of infrared intensities four major effects were examined: (a) the magnitude of electron correlation effects, (b) the applicability of the Hellmann–Feynman theorem to the calculation of dipole moments functions, (c) basis set requirements, and (d) the accuracy of the customary harmonic approximations. The calculated infrared intensities for the water molecule and several of its isotopic derivatives are in good agreement with the available experimental data. In addition to the fundamentals the intensities of several overtone and combination bands were also calculated resulting in generally very small values that strongly depend on the potential energy surface used in the generation of vibrational wave functions.
Translational diffusion of chain polymers. II. Effect of internal friction
Authors: Fixman Marshall
Published: July 2002

The translational diffusion constant D0(λ) of chain polymers has been evaluated for models that contain internal friction measured by a strength parameter λ. D0(λ) is an upper bound to the true diffusion constant D(λ). The method of evaluation is based on the facts that the power series expansion of D0(λ) in λ is a series of Stieltjes, and the coefficients in this power series permit a rapid evaluation from equilibrium simulations. Convergent Padé approximants are therefore available. Results are reported for theta point chains with N beads, including Gaussian and lattice models, with N≤1792. In the limit λ→∞, D0(λ) approaches the translational diffusion constant of a chain that diffuses as a rigid body, and this diffusion constant D0(∞) is known to be a lower bound to D(λ). The two main findings are these: First, D0(∞) is approached very closely by D0(λ) for fairly modest values of λ, comparable in size to ordinary bead friction constants. Second, the ratio RG/RH of radius of gyration to hydrodynamic radius, which is the same as D0(λ)/D0(0), seems to have a limit at N→∞ which depends on the backbone model, and probably depends on the bead friction constant. That is, as a result of fluctuations in hydrodynamic interaction the translational diffusion constant fails to satisfy universality. The deviations seem to be rather small for this transport property, on the order of 5%.
A sum rule for vibrational circular dichroism intensities of fundamental transitions
Authors: Polavarapu P. L.
Published: July 2002

A simple expression is derived for the sum of vibrational circular dichroism (VCD) intensities of fundamental transitions. This expression indicates that the VCD sum can be zero for three different types of molecular systems. The nonzero sum in other molecular systems depends upon the molecular electric dipole moment, quadrupole moment, and moment of inertia at equilibrium geometry.
Free jet infrared absorption spectroscopy of the ν3 band of SeF6
Authors: Takami Michio
Published: July 2002

The ν3 band of SeF6 is studied at a low rotational and vibrational temperature using a tunable diode laser. Infrared absorption in pulsed supersonic free jet of SeF6 is observed by phase sensitive detection synchronized with the pulse frequency. Vibration-rotational lines of five isotopic species, 82SeF6, 80SeF6, 78SeF6, 77SeF6, and 76SeF6, are measured between 776 and 790 cm−1 with a Doppler-limit resolution. Five molecular constants, ν3, B3, Bζ3, α220, and α224 are determined for each isotopic species. Isotope shift for the ν3 band is determined to be −1.61 cm−1/amu.
Perturbation analysis of the generator coordinate approximation
Authors: Deumens E. , Lathouwers L. , Van Leuven P.
Published: July 2002

A Born–Oppenheimer analysis of the generator coordinate approximation is performed. The order of magnitude of generator coordinate nonadiabatic effects is estimated and their dependence on the electron-nuclear coupling is established. A separation of the nonadiabatic effects into vibrational and rotational contributions reveals their behavior with respect to vibrational and rotational quantum numbers.
Electron affinity of hydroxyl radical
Authors: Chipman Daniel M.
Published: July 2002

Although the hydroxyl radical is known experimentally to strongly bind an electron, Hartree–Fock calculations predict the excess electron to be unbound. The electron affinity of hydroxyl radical is therefore entirely due to differential effects of electron correlation between the neutral and the anion. Provided that sufficient electron correlation is included in the wave functions, it is found that basis set requirements for semiquantitative determination of this property are modest. A standard double zeta Gaussian basis augmented by one shell of diffuse functions on each atom is capable of giving over 75% of the experimental electron affinity. Addition of polarization functions makes a small correction leading to recovery of over 80% of experiment. Convergence with respect to enlargement of the basis set is very slow beyond this point. Through comparison of a series of calculations containing different levels of configuration interaction, it is found that the electron affinity is largely due to certain types of double excitations from the dominant RHF-like reference determinant. One kind involves only intrapair double excitations and is properly regarded as representing intrapair correlations. The other kind, which is just as important, involves products of two single excitations from different pairs. These then represent interpair correlations arising from simultaneous intrapair single excitations. The GVB method leads to poor results, due to the neglect of the latter kind of correlation. The pi electrons give most of the EA, the interaction of the pi electrons with the sigma bonding pair makes a small but significant contribution, and the 1s and 2s oxygen pairs have little effect. Based on this, a simple MCSCF model including only intrapair excitations is found that leads to very good results for the electron affinity without the necessity of obtaining a large share of the total correlation energies. Further refinements to include higher order intra- and interpair effects via complete active space MCSCF have little effect and even large scale CI corrections are small.
On the critical behavior of optical activity of a nonpolar binary liquid mixture
Authors: Lee Dong J. , Kim Shoon K.
Published: July 2002

A statistical mechanical theory is presented for the dielectric tensor of a multicomponent fluid composed of chiral molecules. Explict expressions are obtained for circular dichroism and optical rotation of a binary liquid mixture in the critical region. The expression for circular dichroism suggests an alternative method of determining the critical parameters of a fluid mixture.
A lattice gas model for carbon tetrachloride
Authors: Shinmi Masato , Huckaby Dale A.
Published: July 2002

A lattice gas model of tetrahedral molecules on a bcc lattice was considered in which a lattice site can be either vacant or occupied by a molecule in either of the two orientations in which the bonds of the molecule point toward neighboring lattice sites. If two molecules occupy neighboring lattice sites, they repel with a steric bond–bond repulsion γ if each points a bond toward the other, they attract with an energy ε if exactly one points a bond toward the other, and they attract with an energy δ if neither points a bond toward the other. The Peierls argument was used to prove that an orientationally ordered phase exists in the model at sufficiently low temperatures if 2ε<γ+δ and μ>max {4ε,12ε−4δ}. The equation of state and critical point were calculated using a Guggenheim approximation. The parameters in the model were fitted to experiment using the properties of carbon tetrachloride at the critical point. The condensed phase in the model exhibits the same type of short-range orientational ordering proposed by Nishikawa and Murata to exist in liquid carbon tetrachloride.
The dielectric constant of liquid sulfur
Authors: Greer S. C.
Published: July 2002

The static dielectric constant of liquid sulfur has been measured between 122 and 169 °C with a reproducibility of 0.03%. The dielectric constant decreases with temperature as the polymerization temperature (159 °C) is neared, then increases with temperature above the polymerization temperature. These new data were taken closer to the polymerization temperature than were the earlier data of Baur and Horsma [J. Chem. Phys. 78, 1670 (1974)]; the two data sets are, however, in good agreement. The qualitative behavior of the dielectric constant is explained by assuming an ideal solution of polymeric sulfur in unpolymerized sulfur, using a constant polarizability per atom for unpolymerized sulfur and another, constant, polarizability per atom for polymerized sulfur, together with the extent of polymerization as a function of temperature as calculated by Wheeler, Kennedy, and Pfeuty [Phys. Rev. Lett. 45, 1748 (1980)] from the n→0 model. However, there are differences between the data and the model.
Determination of polarizabilities and van der Waals constants
Authors: Patil S. H.
Published: July 2002

Simple relations are obtained between polarizabilities and van der Waals constants, in terms of ionization energies. We also give expressions for quadrupolar polarizabilities in terms of electron densities. These enable us to obtain reliable values for quadrupolar polarizabilities and van der Waals constants C6 and C8.
Z dependence of the total energy and the electrostatic potential at the nucleus for the isoelectronic atoms with particular reference to the two-electron atoms in their ground state
Authors: Anno Tosinobu , Teruya Hirohide
Published: July 2002

Equations expressing the total energy E and the electrostatic potential at the nucleus V0,A for an isoelectronic series of atoms as functions of atomic number Z have been examined. Based upon the Z−α expansion of Fröman and Hall, it has been found that equations E=(1/2)LZ2+KZ+W2+W′3(Z−α)−1 +W4(Z−α)−2 and V0,A=LZ+K−W′3(Z−α)−2 −2W4(Z−α)−3 work very well in the sense that they can form the basis of constructing very accurate empirical formulas for E(Z) and V0,A (Z) by fitting these equations to the Thakkar–Smith data for the He–like atoms including H−. Superiority of our approach over Gorunganthu and Bonham’s approach based upon the Taylor series expansion is pointed out. Relevance of our formulas with the results of the Z−1 perturbation calculations has been pointed out.
One- and two-dimensional exchange J-resolved CP-MAS NMR spectrum of adamantane
Authors: Takegoshi K. , McDowell C. A.
Published: July 2002

A combined technique of 1D and 2D exchange NMR and J-resolved CP-MAS NMR of dilute spins in solids and its application to study a spin exchange process of abundant spins in solids is described, and demonstrated for powdered adamantane. A high-resolution J-resolved NMR spectrum of a 13C nucleus obtained by applying homonuclear decoupling and magic angle sample spinning is employed to label the spin states of 1H spins bonded to the 13C nucleus. Perspective 2D exchange spectra are employed to map out connectivity between the proton spin states, and the rate constants for the 1H spin exchange involved are determined by 1D exchange NMR techniques. Discussions based on the total energy conservation enable us to conclude that the observed spin exchange processes are to be ascribed mainly to the flip–flop motion of 1H spins; the spin-lattice process is negligible. The rate constant for the flip–flop motion of the proton spins is determined to be (7±2)×103 s−1 at room temperature.
A theoretical investigation of the one- and two-photon properties of porphyrins
Authors: Masthay M. B. , Findsen L. A. , Pierce B. M. , Bocian D. F. , Lindsey J. S. , Birge R. R.
Published: July 2002

The one- and two-photon properties of free base porphin, free base porphin dianion, and the 2,4-substituted diformyl and divinyl analogs of these molecules are studied using a semiempirical SCF-MO formalism (CNDO-π-SCF-MO-PSDCI) including extensive single and double configuration interaction. Strongly two-photon allowed states are predicted to lie in the Soret region as well as in the region between the Soret and visible bands. A number of the two-photon allowed states in the Soret region are predicted to have two-photon absorptivities exceeding 100×10−50 cm4 s molecule−1 photon−1. The calculations indicate that the visible (Q) states are well characterized by the four orbital model, whereas the Soret (B) states contain significant contributions from configurations comprised of other orbitals. The inclusion of extensive double configuration interaction significantly reduces the Soret-visible (B–Q) splitting, increases the Qx–Qy splitting, and yields calculated oscillator strengths for the Q bands in better agreement with experiment than values calculated using single CI alone. The effects of conjugation into the porphyrin macrocycle are predicted to be more significant than inductive effects on macrocycle π orbitals due to substituent polarity. The 〈Qx‖r‖S0〉 and 〈Qy‖r‖S0〉 transition moment vectors are predicted to lie approximately through adjacent pyrrole rings in 2- and 4-monoformyl free base porphin dianions and approximately through adjacent methine bridges in 2,4-diformyl free base porphin dianion.
Internal state dependence of HCl/Ar(111) desorption rates
Authors: Adams John E.
Published: July 2002

The rate of desorption of HCl from an Ar(111) surface as a function of the internal state of the physisorbed molecule is studied via a quasiclassical trajectory simulation of the system dynamics. Results from these calculations indicate that the desorption rate passes through a maximum at an initial rotational quantum number of 6, with the maximum rate being enhanced but the rate behavior not being altered qualitatively when a quantum of vibrational energy is added to the molecule. This observed rate dependence may be understood in terms of a transition of the system between distinct dynamical regimes that occurs as the rotational energy of the molecule is increased. Surface of section plots analogous to those used in the study of intramolecular energy transfer are found to provide a convenient means for identifying a transition of this sort.
A variable energy photoelectron study of the valence levels and I 4d core levels of CF3I
Authors: Yates B. W. , Tan K. H. , Bancroft G. M. , Tse J. S.
Published: July 2002

Using monochromatized synchrotron radiation, gas phase photoelectron spectra of CF3I have been obtained between 21 and 100 eV photon energies. Experimental valence band branching ratios have been compared with theoretical branching ratios from MS-Xα calculations. The generally good agreement between experiment and theory confirms the orbital assignment: 4e<4a1<1a2∼3e<2e<3a1<1e∼2a1 <1a1, in order of increasing binding energy. In contrast to CF4, MS-Xα calculations predict two shape resonances for CF3I at 15.2 eV (e channel) and 17.2 eV (a1 channel). Experimentally, weak shape resonances are observed on e orbitals at ∼14 eV kinetic energy. The cross sections are very useful for correlating orbitals in CF3I with those of CF4. For example, the cross sections suggest that the 3e orbital in CF3I correlates with the 1t1 orbital rather than the 4t2 orbital in CF4. After the onset of the I 4d level at ∼57 eV, intershell coupling becomes important in enhancing valence band levels having high I 5p character such as the 4e orbital. The I 4d branching ratio from 66 to 110 eV is similar to the Xe 4d branching ratio in atomic Xe, indicating atomic-like behavior for the I 4d subshell.
Ordering in the parallel hard hypercube gas
Authors: Kirkpatrick T. R.
Published: July 2002

Ordering in the hard hypercube gas model is discussed. An exact application of density functional theory in the limit of high dimensionality leads to the conclusion that an ordering transition to a simple hypercube lattice occurs at a critical density of hypercubes. The transition is continuous. The structure of the theory suggests a similar transition at finite dimensionality. The critical dynamics below the transition are also computed.