bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluctuations of spherical microemulsions
Authors: Safran S. A.
Published: February 2003

A statistical model for microemulsions is used to study the stability of a single phase of spherical droplets to thermal fluctuations. The amplitude of size (l=0 spherical harmonics) and shape (l=2) fluctuations are calculated as a function of the concentration and temperature. The divergences in these fluctuations are shown to define a range of stability for the spherical droplet phase.
The theory of double-beam three-photon absorption. II. Polarization ratio analysis
Authors: Andrews David L.
Published: February 2003

This paper further develops the theory of double-beam three-photon spectroscopy introduced in part I. A much simpler method than that described previously is proposed for the experimental characterization of the three-photon excited states, where measurement of two polarization ratios alone suffices for a complete analysis. A comprehensive classification of the excited state symmetries is provided for the common molecular point groups.
An electron spin echo envelope modulation study of lithium nuclear hyperfine and quadrupole coupling in the A(Ti–Li) center of α-quartz
Authors: Isoya J. , Bowman M. K. , Norris J. R. , Weil J. A.
Published: February 2003

Computerized microwave pulse generation and detection with subsequent Fourier transformation of electron spin echo envelope modulation spectra has been used to measure the small 6,7Li nuclear superhyperfine and quadrupole splittings of a lithium-compensated titanium(3+) center in single crystal α-quartz. Comparison of the 7Li hyperfine matrices Ā determined from standard cw-EPR and from ESEEM show excellent agreement. The precision is better by an order of magnitude for the latter, with uncertainties on the order of one part in a thousand. Use of a three-dimensional display technique yielded the relative sign of matrices Ā and Q̄ for 7Li.
KVV Auger spectrum of F2: The importance of hole–hole correlation
Authors: Weightman P. , Thomas T. D. , Jennison D. R.
Published: February 2003

The KVV Auger spectrum of F2 has been measured and analyzed in terms of theoretical models of different levels of sophistication. In contrast to the corresponding spectra of many small molecules, this spectrum cannot be described in terms of an independent-particle model. The approach suggested by Thomas and Weightman, which allows in an approximate way for hole–hole interaction, gives noticeably improved results. A more accurate, configuration-interaction treatment developed by Jennison gives reasonable agreement with experiment. Peak assignments based on comparison of this theory with the experimental spectrum have been made. This spectrum provides a very clear case where hole–hole correlation effects are important. The experimental spectrum is unusual in that the lines are generally narrow, in contrast to many KVV spectra, which often have quite broad lines. The ionization potentials for the 2σg and 2σu orbitals have been measured. The relative cross sections for ionization from these orbitals are equal, suggesting that those orbitals arise almost entirely from fluorine 2s atomic orbitals, with little admixture from 2p.
Rotationally elastic and inelastic collisions: Quantum distorted-wave and semiclassical perturbative analysis of spectral line shapes
Authors: Bonamy L. , Hoang P. Nguyen Minh
Published: February 2003

A quantum theoretical calculation using the distorted-wave and the orbital sudden approximations is presented to explain the observed different j dependences of spectral linewidths at low and high temperatures in pure HD. It is shown that the semiclassical limit of this calculation does not lead to this behavior. Minimization of the mean square deviation between theoretical and experimental linewidths leads to an optimization of the coefficients of the anisotropic Lennard-Jones potential. Nevertheless, the best agreement is obtained with the Farrar–Lee potential without any optimization procedure.
The dynamics of the reaction D+2+C→CD++D at kinetic energies between 0.002 and 14 eV
Authors: Schuette George F. , Gentry W. Ronald
Published: February 2003

Absolute total reaction cross sections and product kinetic energy distributions have been measured for the reaction D+2+C→CD++D over the range of initial kinetic energies between 0.002 and 14 eV. At very low collision energies, the reaction cross section is accurately proportional to the capture cross section calculated for Π approaches of the reactants, taking into account the long-range charge-quadrupole and charge-induced dipole interactions. About 37% of close collisions on Π surfaces lead to CD++D reaction products. Reactions on Σ surfaces are inhibited at low kinetic energies by a strongly repulsive charge-quadrupole interaction at large separations. The reaction is direct at all kinetic energies, with the CD+ product scattered preferentially in the direction of the incident C atom. The reaction is extremely exoergic, and the CD+ product is formed with an internal energy very near its dissociation limit over a large range of collision energies. Although the experimental results do not give direct information on the electronic state pathways to the observed products (except that the reactants approach asymptotically on Π surfaces), the electronic state correlations suggest a low-energy adiabatic pathway to the CH+ (3Π) first excited state of the products, which is consistent with both the measured values of the reaction cross sections and the reaction energetics.
Boundary conditions and reversibility in diffusion controlled reactions
Authors: Monchick Louis
Published: February 2003

Two simple models are explored in which a newly formed reaction product relaxes by internal radiationless transitions between its bound states and by redissociation and diffusion of the reactants back into the solvent. The boundary condition linking the diffusion and reaction processes is found to be of the radiation–convolution form, first derived by Northrup and Hynes. However, the kernel or memory function of the convolution is found to consist of a set of N relaxation modes for the first model (N is the number of bound states) and an infinite denumerable set in the second model which presupposes the Smoluchowski equation in the reaction zone and in the body of the solvent. The two level model is discussed in detail and is found to lead to the usual irreversible form of the boundary condition at intermediate times and to a somewhat unexpected form close to equilibrium.
The Compton profile of neon: Experimental study beyond the impulse approximation
Authors: Lahmam-Bennani A. , Duguet A. , Rouault M.
Published: February 2003

High-precision relative energy-loss spectra of 25 keV electrons scattered from neon atoms are measured in the momentum transfer range 0.5 a.u.<K< 15 a.u. The corresponding generalized oscillator strengths are made absolute by use of the Bethe sum rule and then converted to Compton profiles (CP). These CP’s are shown to be K-independent in the K ranges 5–7 and 13–15 a.u., where effective valence and total CP’s are respectively defined. Neither of these profiles is reproduced by the impulse approximation (IA) because of the existence of the so-called Compton defect, i.e., a lack of symmetry in the intensity of the observed profile on the positive and negative q sides (q is the usual Compton parameter), and a shift of its maximum from the q=0 position predicted by the IA. Following a theoretical treatment proposed by Tavard and co-workers for H and He, the experimental profiles are divided into their symmetrical (SCP) and antisymmetrical (ASCP) parts with respect to the q variable: the ASCP agrees with Tavard’s qualitative predictions, while the SCP is not reproduced by the IA. The remaining difference might be attributed to higher order terms in Tavard’s series development of the Born operator. Comparison of our results to previous experimental ones is also given.
On sum rules and Stillinger–Lovett conditions for inhomogeneous Coulomb systems
Authors: Carnie Steven L.
Published: February 2003

We show that, for the case of a Coulomb fluid bounded by a planar surface, the inhomogeneous Stillinger–Lovett condition is a consequence of the dipole moment sum rule of Blum et al. [J. Chem. Phys. 75, 5974 (1981)]. We also give a new derivation of the Stillinger–Lovett condition, valid for both homogeneous and inhomogeneous systems, which is entirely analogous to the derivation of the dipole moment sum rule. Our new derivation enables us to clarify certain subtleties that arise when image forces are present. We comment briefly on the generalization of these sum rules to systems of particles with higher multipole moments (e.g., ion–dipole mixtures).
Topological distribution functions of ring polymers II. Theory and computer simulation
Authors: Iwata Kazuyoshi
Published: February 2003

Reliability of the methods used in constructing a topological rubber-elasticity theory [K. Iwata, J. Chem. Phys. 76, 6363, 6375 (1982)] is examined in two-ring-polymer systems. This system has been studied in part I [K. Iwata and T. Kimura, J. Chem. Phys. 74, 2039 (1981)], where the ‘‘topological moment (or the first) method’’ has been presented. In this paper, (i) another new method called ‘‘contact series expansion (or the second) method’’ is proposed, (ii) computer simulations for 6-choice-simple-cubic-lattice-model polymers are performed, and (iii) it is found that the first method leads to a good agreement in topological distribution functions, while the second one leads to a good agreement in topological moments with the simulations.
Local mode predictions for excited stretching vibrational states of HCCD and H 12C 13CH
Authors: Halonen L. , Noid D. W. , Child M.S.
Published: February 2003

Calculation are performed for the stretching vibrational states of acetylene HCCD and H12C13H on the Oak Ridge computing systems. The results of these calculations agree with the recent observations by photo-acoustic spectroscopy. (AIP)
Monte Carlo simulation of diffusion of gases in a porous solid: Calculations for a new class of solids
Authors: Nakano Y. , Evans J. W.
Published: February 2003

In a previous paper, a Monte Carlo simulation of the Knudsen diffusion of a gas in a porous solid was carried out. The simulated porous solid had pore walls that were convex. In the present paper, the simulation is repeated using simulated solids whose pore walls are concave. It was found that the results of both studies could be correlated by a single equation. This equation enables the prediction of the Knudsen diffusiveness from the porosity and mean pore size without resort to a tortuosity factor.
Harmonic surface entropy of noble gas crystals: Cell cluster method
Authors: Kincaid Robert H. , Huckaby Dale A.
Published: February 2003

The harmonic surface entropy was calculated for fcc and hcp crystals with first-neighbor interactions. The crystals chosen had shapes of minimum lattice energy under first-neighbor interactions. Although the bulk harmonic entropy is higher for fcc than for hcp crystals, the surface harmonic entropy was found to be higher for hcp than for fcc crystals. In fact, the overall harmonic entropy was found to be higher for hcp than for fcc crystals having fewer than a few thousand atoms.
Calculations of drift velocity of electrons in inert gases at low E/N
Authors: Hayashi M. , Ushiroda S.
Published: February 2003

The zero field reduced mobilities of electrons μ0 in helium, neon, argon, krypton, and xenon have been calculated as a function of gas temperatures T using the Boltzmann equation and compared with the values of the thermal electron mobilities of electrons μN obtained by Mozumder [J. Chem. Phys. 72, 6289 (1980)]. Discussion has been made about the large discrepancies between the measured and calculated values of μN in neon which were pointed out by Mozumder. The calculated exact drift velocities W in helium as a function of E/N and T have been compared with the experimental results of W for wide E/N and T ranges. A summarized figure is shown for anomalous electron mobilities in helium as a function of N at low E/N.
Particle–antiparticle annihilation in diffusive motion
Authors: Toussaint Doug , Wilczek Frank
Published: February 2003

We study both numerically and analytically the time development of a system of particles and antiparticles moving diffusively and annihilating irreversibly. The asymptotic behavior is found to depend dramatically on whether the initial fluctuations are localized or entirely random. Physical examples of each kind are identified.
Enthalpies of formation of naphthalene TCNQ, anthracene TCNQ, TMPD, and TMPD TCNQ, and experimental crystal binding energies of mixed simple regular lattices
Authors: Metzger Robert Melville , Arafat El Sayed
Published: February 2003

The standard enthalpies of formation ΔH°f[naphthalene TCNQ(c), 298.15 K]=716.95±7.30 kJ/mol, ΔH°f[anthracene TCNQ(c), 298.15 K] =763.84±4.87 kJ/mol, and ΔH0f[TMPD(c), 298.15 K]=39.60±3.85 kJ/mol were measured by oxygen combustion calorimetry. Then, the states naphthalene TCNQ(c), anthracene TCNQ(c), and TMPD TCNQ(c) are more stable by 30.01±7.63, 30.31±5.26, and 82.08±4.34 kJ/mol than the states [naphthalene(c), TCNQ(c)], [anthracene(c), TCNQ(c)], and [TMPD(c), TCNQ(c)], respectively; they are more stable than the gaseous neutral ions by 203±12, 232±12, and 230±10 kJ/mol, respectively. Therefore, the choices of different lattices and ionicities are determined not by the thermochemical results given above, but by a subtle interplay between the cost of ionization ID–AA and the various charge-dependent contributions to the theoretical cohesive energy.
Potential energy surface for the study of inelastic collisions between nonrigid CO and H2
Authors: van Hemert M. C.
Published: February 2003

The electron gas model is employed to compute the first order part of the potential for the interaction between CO and H2. The intra- and intermolecular distances were varied over the range considered important for vibrationally inelastic scattering. The potential consisting of 4158 points is represented analytically by a spherical expansion for the angular part. The distance dependence of the expansion coefficients is given by polynomials. The isotropic second order dispersion energy was estimated from dipole oscillator strength distributions and sum rule ratios for CO and H2. The isotropic part of the complete potential thus obtained agrees better with results derived from molecular beam scattering data than previous potentials.
Dynamics of association and decay. A model study of Cl−+Cl2 ⇄  Cl−*3 using quasiclassical trajectories
Authors: Babcock Lucia M. , Thompson Donald L.
Published: February 2003

Quasiclassical trajectories on a model potential-energy surface have been used to study Cl−+Cl2 ⇄ [Cl−3]*. Rate coefficients are reported for both the forward and backward processes. Decay rate constants as a function of energy and thermal rate coefficients for forming [Cl−3]* complexes that live for a given number of inner turning points in the Cl−+Cl2 relative motion are reported.
The structure and dynamics of hydrogen in Mg2NiH4 studied by elastic and inelastic neutron scattering
Authors: Noréus D. , Olsson L. G.
Published: February 2003

The hydride Mg2NiH4 exhibits a phase transition from a low temperature to a high temperature phase at about 508 K. The dynamics of the hydrogen in the high temperature phase have been studied by cold neutron scattering experiments. According to these, the hydrogen atoms showed a high mobility, but the motion was mainly localized, in some way, on the six available octahedral positions around each nickel atom. The translational diffusion coefficient appeared simultaneously to be very small, within the instrumental resolution, implying values <10−6 cm2/s. Assuming a simple diffusive behavior in spherical symmetry for the localized part of the motion, relaxation times in the order of 10−11 s were obtained for the jumps of the hydrogen atoms. The low temperature phase of Mg2NiH4 was also studied indicating no other mobility of the hydrogen atoms than a vibrational motion, the low frequency part of which could be reproduced by a Debye spectrum with the temperature 150 K. In order to characterize the sample, a structure analysis was made on the high temperature phase of Mg2NiD4 using neutron diffraction. The structure data were in agreement with results recently reported, but anisotropic temperature parameters could be observed.
Equilibrium bond lengths related to nuclear charge and atomic energies for homonuclear diatoms
Authors: Pucci R. , March N. H.
Published: February 2003

An approximate argument is given, from the 1/Z expansion for homonuclear diatoms, that (R2e/Z5/3)E vs ZR3e should be a universal function, Re being the equilibrium internuclear distance, Z the charge on each nucleus, and E the total energy. This has motivated a plot which is remarkably linear for B2, C2, N2, and F2. Their equilibrium bond lengths therefore can be calculated from the relation E=aZ8/3Re+bZ5/3/R2e, where a=8.53, b=60.42, all quantities being in a.u.. In this relation the molecular binding energy is very small compared with the atomic energies and therefore the equilibrium distance is determined essentially by (a) the atomic energy and (b) the nuclear charge. For heavier diatomics, the regularities predicted from the 1/Z expansion are again found.
Chemical potential related to total energy in isoelectronic sequences of positive ions
Authors: March N. H. , Pucci R.
Published: February 2003

Using the 1/Z expansion of the total energy E(Z, N) of atomic ions of nuclear charge Z and having N electrons, the chemical potential μ is shown to be approximately related to E by the equation μ=αE+β+γ √δ+4ε0E   (i). Here, α and ε0 are functions of N which are determined solely by the hydrogen problem, while the quantities β(N),γ(N), and δ(N) are known from the 1/Z expansion. A similar analysis of the 1/Z expansion allows I+A to be calculated as a function of E, and its close relationship to μ is demonstrated. To demonstrate the usefulness of the relationship (i), the Hartree–Fock calculations of Clementi are used for E(Z, N). The result of Alonso and March that μ in Hartree–Fock theory is the Koopmans ionization potential enables the relation (i) to be tested for N≤10 for a wide range of Z. It is pointed out that in the statistical limit of N and Z both large, but N/Z≤1, Eq. (i) is replaced by a universal curve relating μ/N4/3 and E/N7/3. Finally, in an appendix, we establish the connection between the Euler equation of the density functional treatment of Hartree–Fock theory and the Schrödinger equation for the highest occupied molecular orbital (HOMO).
The structure of (H3O2)−
Authors: Rohlfing Celeste McMichael , Allen Leland C. , Cook Charles M. , Schlegel H. Bernhard
Published: February 2003

Global geometry optimizations of the hydroxide hydrate anion (H3O2)− are performed at the 4-31G, 6-31G*, and 6-31G** levels to determine its structure. Further geometry searches are carried out using configuration interaction with double substitutions, and Mo/ller-Plesset perturbation theory to second and third order. An asymmetric hydrogen bond is found at the SCF level, while a symmetric structure results when correlation is included. Comparisons are made to previous theoretical studies of (H3O2)−, and also to recent x-ray crystallography results. An analysis of the larger correlation energy in the symmetric case is given.
Study of sulfur-containing molecules in the EUV region. III. Photoexcitation of CS2
Authors: Wu C. Y. Robert , Judge D. L.
Published: February 2003

Using synchrotron radiation as a continuum background, the absorption cross section of CS2 has been measured using a double ionization chamber. The cross sections range from four to a maximum value of 65 Mb in the 175–760 Å region. Two new Rydberg series X and XI have been identified and apparently converge to the D̃ 2Πu state of CS+2 at 16.943 eV.
EPR study of oriented photoexcited triplets of zinc porphyrin in a discotic liquid crystal: Evidence for axial symmetry in the condensed phase
Authors: Gonen O. , Levanon Haim
Published: February 2003

An EPR study of the photoexcited triplet of ZnTPP in the dicostic mesophase of p-n-hexa-hexyloxytriphenylene is reported. The results indicate that (i) the observed spectra are temperature independent (between ∼100–140 K) and typical of axially symmetric guest molecules, with zero field splitting values ‖D‖=0.0308 cm−1, and ‖E‖=0, (ii) the line intensity of the out-of-plane canonical orientation of the guest molecules exhibits anisotropic patterns with respect to the sample orientation in the external field. These results are best interpreted by the columnar structure of the host mesogen which forms rodlike structures whose directors are distributed about a plane perpendicular to the applied external magnetic field with a normal distribution and standard deviation of ∼3–8°. The ZnTPP guest molecules are located outside the columns and orient such that the porphyrin planes are parallel to the columns axes. It is also concluded that, in the temperature range studied, the porphyrin molecules are distributed in this liquid crystal as noninteracting monomers retaining their axial symmetry.
Atom–matrix interactions: An MCD study of copper atoms in argon
Authors: Zeringue Kyle J. , ShakhsEmampour Jalal , Rivoal Jean-Claude , Vala Martin
Published: February 2003

The absorption and MCD spectra of the 2P ← 2S transition of Cu atoms isolated in argon matrices have been measured over the temperature range 13–25 K. Spectral band moments (up to third order in MCD) have been determined and parameters of interest extracted from them. The observed triplet bands’ separation and MCD 𝒞 term signs are analyzed assuming a static trigonal site distortion. It is shown that a static site distortion model is incapable of reproducing the experimental results. Simultaneous spin orbit and noncubic lattice vibrational couplings (Jahn–Teller effect) are shown to be active in the Cu excited 2P state. The observed triplet of bands and its MCD 𝒞 terms are satisfactorily described by an adiabatic model developed by Moran. Comparison of the observed band shape to ones calculated by Cho using Monte Carlo methods show that simultaneous spin-orbit and e and t2 lattice mode interactions are operative. The observed reduction of 25% in the excited state spin-orbit coupling constant is attributed to the overlap of Cu 4p orbitals with the Ar 3p orbitals. A new method for the determination of the temperature of matrix-isolated samples is described. The temperature dependence of the MCD first moment and absorption zeroth moment of a matrix-isolated paramagnetic species is determined once to find the lowest temperature attainable.
Analysis of infrared absorption line shapes in condensed media: Application of a classical limit of Heisenberg’s equations of motion
Authors: Diestler D. J.
Published: February 2003

A microscopic dynamical treatment of chemical systems comprising both light particles that require a quantal description and heavy ones that may be described adequately by classical mechanics is presented. A (partial) classical limit of Heisenberg’s equations yields a self-consistent set of ‘‘hemiquantal’’ equations (HQE) of motion. The adiabatic limit of the HQE, in which energy is not shared between high-frequency modes of the quantal subsystem and relatively low-frequency modes of the classical subsystem, is applied to a one-dimensional model for infrared absorption by matrix-isolated impurites. The predictions of the model are consistent with recent experimental measurements on the ‘‘Q’’ feature of HCl isolated in Ar.
Vibrational study of CsH2PO4 and CsD2PO4 single crystals
Authors: Marchon B. , Novak A.
Published: February 2003

The infrared and Raman spectra of disordered paraelectric and ordered ferroelectric phases of CsH2PO4 and CsD2PO4 single crystals have been investigated at various temperatures in the 4000–10 and 4000–0 cm−1 range, respectively. An assignment of lattice and internal vibrations in terms of symmetry species and approximate type of motion is given. Most of the external vibrations of the paraelectric phase follow the selection rules of the C2h factor group symmetry, whereas the internal modes do not obey the mutual exclusion rule. The Raman spectra of the ferroelectric phase show TO-LO splitting up to 50 cm−1 for a number of lattice and internal vibrations which is correlated with infrared intensities. Disordered short and ordered long hydrogen bonds are distinguished spectroscopically and the OH stretching and bending frequencies are correlated with x-ray and neutron diffraction data. A large positive isotope effect on the short hydrogen bond is manifested by a low (1.13)νOH/νOD frequency ratio. The short OH⋅⋅⋅O, but not OD⋅⋅⋅O, bond contracts at higher temperature as shown by the increased hydrogen bond and decreased OH stretching frequency. The Raman intensity of the 74 cm−1 mode and 507 cm−1LO band plot vs temperature gives a curve of the order parameter type. The half-width of the OH⋅⋅⋅O Raman band increases three times more steeply with increasing temperature than that of the OD⋅⋅⋅O band which is ascribed mainly to a larger activation energy of the proton jumps along the OD⋅⋅⋅O bond.
Infrared laser optogalvanic spectroscopy of molecules
Authors: Webster Christopher R. , Menzies Robert T.
Published: February 2003

Infrared laser optogalvanic spectra of portions of the NH3 ν2 band at 9.5 μm and the NO2 ν3 band at 6.2 μm have been recorded using cw tunable diode lasers to probe dc electrical discharges in pure NH3 and an NO2/He gas mixture. Two contributions to the optogalvanic signal are identified: one which corresponds to an increase in discharge impedance and is seen only for irradiation of the negative glow region; and a second which corresponds to a decrease in discharge impedance and is seen for irradiation of all other discharge regions and the volume outside the interelectrode region. Mechanisms by which infrared laser irradiation may cause impedance changes in the discharge are proposed.
Optoacoustic measurements of IR multiphoton excitation of cis-3, 4-dichlorocyclobutene
Authors: Presser Nathan , Barker John R. , Gordon Robert J.
Published: February 2003

Optoacoustic detection was used to study the infrared multiphoton excitation of cis-3,4-dichlorocyclobutene (DCCB). The dependence of the optoacoustic signal SOA on DCCB pressure PDCCB, on Ar buffer gas pressure PAr, and on laser fluence φ were studied systematically. It was observed that SOA is proportional to PDCCB and increases monotonically with PAr, leveling off at PAr∼10 Torr. Absolute calibration of SOA was achieved by measuring the attenuation of the laser beam. It was found that the average number of photons absorbed by DCCB n̄ varies as 5.4 φ0.85, where φ is expressed in J/cm2. It is shown that the buffer gas pressure dependence of SOA can be used to deduce the vibrational relaxation rate of the excited molecule. The fluence dependence of n̄ is predicted quantitatively by numerical solution of the master equation, including collision terms. It is assumed in this calculation that the infrared absorption cross section is independent of vibrational energy and is equal to the nominal small signal cross section.
Multiple phase-coherent laser pulses in optical spectroscopy. I. The technique and experimental applications
Authors: Warren W. S. , Zewail Ahmed H.
Published: February 2003

In this series of papers we report on the generation and application of multiple pulse phase coherent sequences in optical spectroscopy. In this paper the effects of intense pulse trains on systems with only two resonant energy levels are analyzed, with particular attention to the effects of extreme inhomogeneous broadening and population depletion to nonresonant levels. It is shown that these effects, which are present in virtually all optical systems, make the simple gyroscopic model of optical coherent transients invalid. Exact calculations show, e.g., that a two-pulse photon echo is not maximized by a 1:2 length ratio for the pulses; that the maximum excited state population is not created by a 180° pulse; and that three equal pulses are almost as effective as a 1:2:1 ratio for producing three pulse echoes. The role of pulse phase is extensively analyzed. Pulse sequences are proposed and experimentally demonstrated which permit optical phase sensitive detection and measurement of ground state relaxation parameters. The experimental results are based on an extension of the acousto-optic modulation and fluoresence detection techniques of Zewail and Orlowski [Zewail et al., Chem. Phys. Lett. 48, 256 (1977); Orlowski et al., ibid. 54, 197 (1978)]. The relative merits of fluorescence and transverse polarization detection are discussed, and fluorescence detection is shown to be more generally useful for these new sequences. Finally, composite pulse trains are shown to be capable of substantially increasing the signal available from highly inhomogenously broadened transitions. In paper II we extend the treatment to multilevel systems with some emphasis on solid state applications.
The I(2P1/2)+O2⇄I(2P3/2)+O2(1Δ) equilibrium
Authors: Young A. T. , Houston P. L.
Published: February 2003

The equilibrium between excited iodine atoms and oxygen has been examined by monitoring the time-dependent I*[≡I(2P1/2)] concentration following creation of this species by pulsed laser photolysis of iodine-containing precursors. A double exponential decay is observed which reflects a fast approach to equilibrium followed by a slower relaxation of the equilibrated mixture. Data obtained with the I* precursors HI and CH3I show that the rate constant for the reaction I*+O2→I+O2 is insignificant compared to that for the reaction I*+O2→I+O2(1Δ). Data obtained from the precursors i-C3F7I, n-C3F7I, C2H5I, and CF3I suggest that O2(1Δ) is rapidly relaxed by the precursor itself, by the precursor radical, or by some product formed in a reaction between the precursor radical and oxygen. The rate constant for the process I*+O2→I+O2(1Δ) has been found to be (8.8±0.9)×105 s−1 Torr−1, while that for the process I*+O2→I+O2 is (0.3±1.3)×105 s−1 Torr−1.
Equilibrium properties of molecular fluids with charge distributions of quadrupolar symmetry
Authors: Monson Peter A. , Steele William A. , Streett William B.
Published: February 2003

Molecular dynamics simulations are reported for dense fluids of molecules with discrete charge distributions of quadrupolar symmetry. The nonelectrostatic parts of the intermolecular potentials were modeled by Lennard-Jones site–site interactions with the two sites in each molecule separated by 0.547σ, where σ is the distance scaling parameter in the Lennard-Jones function. The charge distributions were comprised of a double negative charge at the molecular center of symmetry plus two single positive charges placed on the symmetry axis at equal distances from the center. The magnitudes and separation distances of the charges were varied so that changes in the thermodynamic, quasithermodynamic (mean square force and torque), and structural properties of the fluid could be determined at a fixed quadrupole moment. At finite charge separation distances, the multipole expansion yields ideal quadrupole–quadrupole plus higher order interactions. It is shown that the observed changes in thermodynamic properties can be accurately calculated by including the next highest multipole interaction terms in the series; namely, the ideal quadrupole–hexadecapole energies (plus a small contribution from the hexadecapole–hexadecapole terms at the largest charge separations). A low order perturbation theory calculation of the changes in structural properties is also presented; it is found not to give satisfactory values for the observed changes in radial distribution function with charge separation distance.
The interionic potential of mean force in a molecular polar solvent from an extended RISM equation
Authors: Hirata Fumio , Rossky Peter J. , Pettitt B. Montgomery
Published: February 2003

The generalization of a recently proposed extension of the RISM integral equation to infinitely dilute isolated ions and ion pairs in polar, interaction site model, molecular solvents is outlined. An essential element of the development is the explicit separation of the contributions which yield a continuum dielectric solvent model from the remainder. Thus, it is only for this correction that one relies on the integral equation. Application is made to a system consisting of a diatomic polar solvent and atomic ions of varied charge and radius. The results of these calculations show that the present approach produces sensible qualitative features of ionic solvation including an appropriately varying degree of solvent orientational saturation with ionic charge and radius. Correspondingly, the calculated interionic potentials of mean force reproduce the same basic features manifest in already available studies of dipolar hard sphere solvents, including the positions of oscillatory features in the structure and the relatively short spatial range of the corrections to the continuum dielectric theory. A quantitative evaluation of the accuracy of the present predictions is not possible with presently available data.
van der Waals theory of melting in two and three dimensions
Authors: Weeks John D. , Broughton Jeremy Q.
Published: February 2003

In the van der Waals (vdW) equation of state the effect of attractive forces is expressed in terms of a parameter a which is independent of density and temperature. Following Longuet-Higgins and Widom, this simple expression is shown to be qualitatively accurate for systems whose structure is determined mainly by harsh repulsive forces. Molecular dyamics simulations are used to examine the effects of the attractive forces on the structure of the Lennard-Jones (LJ) liquid and coexisting solid near the triple point in three and two dimensions. Implications of the vdW treatment of attractive forces for the melting transition of the 2D LJ solid are discussed.
Vibrational relaxation during gas–surface collisions
Authors: Misewich J. , Plum C. N. , Blyholder G. , Houston P. L. , Merrill R. P.
Published: February 2003

The probability for deactivation of CO2(001) has been found to be 0.22 for collisions with a stainless steel surface, 0.16 for silver, and 0.20 for nickel. The probability for deactivation on the silver surface was invariant with surface temperature in the range from 298 to 473 K. A pulsed CO2 laser was used to excite the CO2, while the population of vibrationally excited molecules was monitored by observing their infrared fluorescence at 4.3 μm.
A surface Penning ionization study of the CO/Ni(111) system
Authors: Bozso Ferenc , Yates John T. , Arias Jose , Metiu Horia , Martin Richard M.
Published: February 2003

Metastable He(2 1S) and Ne(3P2,0) beams were used to probe the electronic properties of Ni(111) and CO/Ni(111) surfaces. The metastable atoms collide with the surface and transfer their electronic excitation energy, causing electron ejection. With the Ni(111) surface, the metastable is first resonantly ionized and the ion is subsequently Auger neutralized, giving an electron energy spectrum which is similar to the corresponding low kinetic energy ion neutralization spectrum (INS). Differences between the metastable quenching spectrum and the INS spectrum were observed, and are discussed in terms of the differences in the mechanisms and the ion kinetic energies. With a CO/Ni(111) surface, the CO eliminates direct interaction of the metastable atom with the metal and the surface Penning ionization electron spectrum (SPIES) is obtained. The SPIES spectrum is much more surface sensitive than the corresponding UPS spectrum, since there is no background due to primary electron emission from the metal which dominates the UPS spectrum. SPIES peaks corresponding to electron emission from the 4σ, 1π+5σ, and 2π* orbitals of CO were observed and investigated as a function of surface coverage and temperature. Under certain coverage and temperature conditions a state of CO is found (associated with a weakly bound state in the thermal desorption spectrum) which has enhanced 1π+5σ and 2π* peaks and this is attributed to tilting of the CO molecules in this state with respect to the surface.
Isotope enrichment during the formation of water clusters in supersonic free jet expansions
Authors: Kay Bruce D. , Castleman A. W.
Published: February 2003

Presently, investigation of the dynamics, energetics, and structure of microscopic molecular clusters constitutes an active area of research in chemical physics. Herein the RRKM theory of primary isotope effects is extended to qualitatively predict isotope enrichment in water cluster formation. The theoretical model is verified experimentally by neutral free jet expansion modulated molecular beam mass spectrometry of mixed (H2O)m(D2O)n clusters. The results further support the previously presented mechanism for neutral cluster growth in free jet expansions. The observed enrichment factors (∼30%) suggest that techniques involving clustering may find practical applications in the area of isotope separation.
Vibrational relaxation of HCN(002)a)
Authors: Hastings Peter W. , Osborn Martin K. , Sadowski Chester M. , Smith Ian W. M.
Published: February 2003

Tuned output from an optical parametric oscillator has been used to excite HCN to its (002) level for measurements of vibrational energy transfer. By observing time-resolved (002,001) fluorescence in the presence of different collision partners, the following rate constants (k002/cm3 molecule−1 s−1) were obtained for relaxation of HCN(002) at 298±4 K: kHCN=(6.8±0.4)×10−12; kHe=(5.6±0.25)×10−15; kNe=(3.8±0.16)×10−15; kAr= (3.0±0.4)×10−15; kKr=(3.25±0.12)×10−15; k02=(1.39±0.08)×10−14; kN2=(2.6±0.15)×10−14; kCO=(6.8±0.4)×10−14. These results are compared with the rate constants (k001) obtained for relaxation of HCN(001) and the mechanisms for relaxation are discussed. With noble gases as collision partners, the ratios (k002/k001) are less than one. Comparison of these ratios with predictions of the ‘‘breathing sphere’’ theory indicates that relaxation of HCN(00v3=1,2) occurs via transfer to HCN (120 {v3−1}), the lower rate for v3=2 being due to the increased energy gap between initial and final states.
Very low energy collision induced vibrational relaxation of 1A
u glyoxal
Authors: Jouvet Christophe , Sulkes Mark , Rice Stuart A.
Published: February 2003

We report the results of a study of very low energy collision induced vibrational relaxation of 1Au glyoxal. The effective collision energy is found to be different for different initial vibronic states, and the final states populated are drawn from a small subset of all available final states. The observed pathways of relaxation are interpreted using a previously proposed orbiting resonance model for the He: glyoxal collisions. It is inferred that (i) single collision–single quantum transfers dominate the relaxation process, and (ii) when there are near degeneracies in the vibrational manifold the lowering of symmetry in the orbiting resonance can permit mode mixing that is prohibited in the isolated molecule.
Stochastic classical trajectory approach to relaxation phenomena. III. Comparison of trajectory results to quantum mechanical perturbation theory
Authors: Nitzan Abraham , Tully John C.
Published: February 2003

A simple model representing an impurity oscillator coupled anharmonically to a lattice is examined both by quantum mechanical perturbation theory and by stochastic classical trajectory simulations. Energy relaxation rates are computed as a function of temperature. Classical and quantum relaxation rates are found to agree well at high temperatures but, as expected, diverge drastically at low temperatures. If zero-point motion of the lattice is incorporated into the classical calculation, classical and quantum relaxation rates agree quite well for all temperatures, even for T→0. This suggests that the stochastic classical trajectory method can provide an accurate description of relaxation phenomena even at very low temperatures.
Classical and quantum dynamics of long lived doubly excited vibrational states of triatomic molecules
Authors: Hedges Richard M. , Reinhardt William P.
Published: February 2003

Local mode A–B–A triatomic molecules are modeled as coupled Morse oscillators using classical and quantum techniques. Classical studies indicate large volumes of nondissociating classical phase space, even well above the dissociation threshold. The trapped classical motion corresponds to excitation in both bond modes of the system. Quantum studies have been performed as a function of coupling constant (mass ratio) and of dissociation energy. Quantum doubly excited vibrational resonances are found with lifetimes of up to 106 vibrational periods. The lifetimes of the states, as ℏ (or dissociation energy) is varied, are in accordance with the correspondence principle. Substantial deviation from the predictions of statistical theories is noted in the distributions of lifetimes, as well as in the fact that all of the resonances are only weakly coupled to the ‘‘direct’’ dissociation channels.
Collision dynamical information from pressure broadening measurements: Application to carbon monoxide
Authors: BelBruno Joseph , Gelfand Jack , Rabitz H.
Published: February 2003

Self- and helium-broadened carbon monoxide linewidths have been inverted to obtain state-to-state rate constants using the energy corrected sudden scaling formalism. Selected rotation–rotation and rotation-translation rate constants are discussed as a function of vibrational and rotational levels for the CO–CO and He–CO systems. We find that there is no dependence of the collision dynamics upon the vibrational state of the collision partners up to v=3. In addition, relaxation in both these systems is found to be dominated by rotation-translation collisions. However they are qualitatively different in their dynamical characteristics and result in signficantly varied state-to-state rate constants. An analysis of the effect of collision partners in the CO–X (X=CO, He, Ne, Ar, Xe, H2) system is presented. Comparisons are made with the available data in the literature.
Rotational predissociation of the Ar⋅HCl van der Waals complex: Close-coupled scattering calculations
Authors: Ashton C. J. , Child M. S. , Hutson Jeremy M.
Published: February 2003

We report an extensive computational study of rotationally predissociating metastable states of the Ar⋅HCl van der Waals complex, using a highly realistic empirical intermolecular potential recently proposed by Hutson and Howard. The states are characterized by fully converged, close-coupled, scattering calculations. Resonance energies, widths, and partial widths are extracted by fitting the energy dependence of S matrices. Total angular momenta of 0 and 1 are studied, and the calculations span an energy range from 0 to 1400 cm−1. The resonance widths vary from <10−4 to ≳5 cm−1, and it is shown that the isolated narrow resonance approximation is of poor validity for the wider resonances. Comparison of the close-coupling results with approximate calculations enables assignment of approximate quantum numbers to the metastable states. Physical explanations are suggested for the strong trends in resonance parameters as a function of the intermolecular stretching, diatom rotation, and molecule-fixed angular momentum projection quantum numbers. A changeover from a near-molecule-fixed to a near-space-fixed coupling scheme, as angular momentum is increased, is clearly demonstrated. The results are of considerable relevance to the design of experiments and the development of approximate computational methods in this area.
Predissociation of HD–Ar van der Waals molecules by internal rotation
Authors: Hutson Jeremy M. , Le Roy Robert J.
Published: February 2003

Accurate close-coupling calculations of level energies and widths of predissociating levels of HD–Ar have been carried out using the Le Roy–Carley BC3 potential for H2–Ar. The calculated widths agree well with the experimental data of McKellar. The principal product from predissociation of HD(v=1, j=2)–Ar is HD in its v=1, j=1 state. This channel is symmetry forbidden for H2(1, 2)–Ar, and its presence accounts for the much larger spectroscopic linewidths found for HD–Ar.
Restatement of conventional electronic wave function determination as a density functional procedure
Authors: Nyden Marc R. , Parr Robert G.
Published: February 2003

It is shown how any conventional ground-state electronic wave function determination starting from a basis set of orthonormal spatial orbitals fk may be restated as a density functional procedure. Write fk=(ρ/N)1/2exp(iθk), with ρ the total electron density, N the number of electrons, and θk a function which may have complex as well as real parts. All matrix elements then are expressible as functionals of ρ and the θk. Orthonormalization gives ∫ρ exp[−i(θ*k−θl)]dτ=Nδkl. With these conditions imposed as constraints, the variational process for determining the energy is equivalent to a procedure for starting from a guessed ρ, determining the θk, determining ρ again, and iterating, with the energy decreasing at each stage. The equations are given and discussed in detail for the four-electron Hartree–Fock problem for which the two orbitals are φ1=(ρ/4)1/2exp(iθ) and φ2=(ρ/4)1/2exp(−iθ), with θ real. A graph of θ is given for the atom Be.
Hydrogen bonds between first-row hydrides and acetylene
Authors: Frisch Michael J. , Pople John A. , Del Bene Janet E.
Published: February 2003

The structures and association energies of the complexes of NH3, H2O, and HF with acetylene have been determined using Hartree–Fock and Mo/ller–Plesset theories. HF is found to act as a proton donor to acetylene, while H2O and NH3 act as proton acceptors.
Electric dipole moments of excited vibrational levels in the X̃ 1A1 state of formaldehyde by stimulated emission spectroscopy
Authors: Vaccaro Patrick H. , Kinsey James L. , Field R. W. , Dai Hai-Lung
Published: February 2003

The electric dipole moments of the 44 (E4ν4=4628.4 cm−1), 2242 (E2ν22ν4)=5770 cm−1), and 2144 (E1ν24ν4=6347 cm−1) levels of H2CO are measured as 2.2723(86), 2.3222(47), and 2.2825(33) D, respectively. This first combination of stimulated emission pumping (SEP) with a static electric field demonstrates the possibility of systematically measuring dipole moments for highly excited vibrational levels of polyatomic molecules in their electronic ground states. The present dipole moment measurements and all previous ones involving overtones and combinations of the C–O stretch (ν2) and out-of-plane bend (ν4) are reduced to two types of expansions. The dipole moment μ is expressed both as an expansion in the normal coordinate displacements and as an expansion through squared terms in the v2 and v4 vibrational quantum numbers.