bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of local translation in the vibrational relaxation of matrix-isolated guest molecules
Authors: Shin H. K.
Published: February 2003

We have studied the participation of local translation in the vibrational relaxation of asymmetric diatomic molecules trapped in a rare gas matrix. For a guest molecule surrounded by six nearest rare gas atoms in a two-dimensional array, it is shown that the role of local translation is to assist vibration-to-rotation energy transfer by producing strong rotation–local-translation coupling and to accept the energy mismatch of initial and final vibration–rotation levels. In the model, low-lying rotational levels are hindered and transformed into libration, and libration-to-rotation transitions take most of the vibrational energy. Applications to hydrogen chloride molecules in Ar show that the 1→0 and 2→1 vibrational de-excitation probabilities of HCl/Ar are significantly smaller than those of DCl/Ar. These probabilities increase only slightly with temperature in the range 9–30 K.
Rate of photochemical protonation and electronic relaxation of excited 1, N6-ethenoadenosine in its aqueous solution
Authors: Takahashi Shinichiro , Nishimura Yoshifumi , Tsuboi Masamichi , Kuramochi Takao , Inoue Yasuo
Published: February 2003

Fluorescence lifetimes and intensities have been examined for 1, N6-ethenoadenosine (εAdo), 1-methylethenoadenosine (m1εAdo+), 9-methylethenoadenosine (m9εAdo+), N1-deazaethenoadenosine (N1 deaza-εAdo), and 9-methyl-N1-deazaethenoadenosine (m 9N1deaza-εAdo+) at various pH′s in the 7.5–0.5 region and at 25 °C. From an analysis, the following conclusions are reached: (1) The strong fluorescence of εAdo is caused by the neutral form (but not protonated form) of its excited state (εAdo*). (2) The protonation of εAdo* takes place at position 9 (but not position 1) with the rate constant of 1.45×1010 s−1 M−1, and the deprotonation of H9 εAdo+* with the rate constant of 1.15×109 s−1, so that the excited state pK*a is 1.10. (3) In the lower pH solution, the fluorescence of εAdo is lowered partly by a proton-induced radiationless transition of the neutral εAdo* itself, and partly through the protonation of εAdo into (εAdoH+)*, which is also subjected to a proton-induced radiationless transition. All of the ten rate constants involved in the relaxation process of εAdo* have been unequivocally determined.
Conformational barriers to internal rotation and vibrational assignment of methyl vinyl ketone
Authors: Durig J. R. , Little T. S.
Published: February 2003

The infrared (3500 to 50 cm−1) and Raman (3200 to 10 cm−1) spectra have been recorded for the gaseous and solid states of methyl vinyl ketone. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. The asymmetric torsion for the s-trans conformer was observed at 116 cm−1 in the infrared spectrum of the gas with two accompanying hot bands and the corresponding torsion of the s-cis conformer was observed at 87 cm−1 with an additional hot band occurring at 84 cm−1. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V1 = 180±9, V2 = 827±107, V3 = 113±8, and V4 = 150±34 cm−1. From these data it has been determined that the s-trans conformer is the predominant form at ambient temperature and the enthalpy difference between the s-trans and s-cis conformers is 280 cm−1 (800 cal/mol) for the vapor. The calculated trans–cis barrier is 827 cm−1 (2.36 kcal/mol) and the cis–trans barrier is 547 cm−1 (1.56 kcal/mol). From the relative intensities of the Raman lines of the liquid at 607 (s-cis) and 537 cm−1 (s-trans) as a function of temperature, the enthalpy difference was found to be 172 cm−1 (492 cal/mol). A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and group frequencies. These results are compared to similar quantities in related molecules.
Experimental investigation of cesium hydride formation by reactive interaction between Cs(7 P) and H2 molecules
Authors: Sayer B. , Ferray M. , Lozingot J. , Berlande J.
Published: February 2003

The radiation of a multimode tunable laser photoexcites cesium atoms from the ground state to the 7 P1/2 level in a mixture of cesium vapor and hydrogen. Cesium hydride is formed by the Cs(7 P)+H2 reaction and observed by laser fluorescence. The relation between the concentration of CsH and those of other species present in the medium [Cs(7 P),H2, and Cs(6 S)] is studied in both a stationary and a transient laser irradiation regime. The rate of CsH formation is found to be proportional not only to [Cs(7 P)] and [H2] but also to [Cs(6 S)]. This observation suggests that, under our experimental conditions {[Cs] = (0.5–8)×1016 cm−3,[H2] = (8–80)×1016 cm−3}, CsH molecules are not created by a direct interaction between Cs(7 P) and H2 but most probably through a two-step reaction. This process might involve intermediate species such as vibrationally excited H2 molecules. An absolute value of the rate coefficient k = {[Cs(7 P)][H2][Cs]}−1d[CsH]/dt?5×10−31 cm6 s−1 is estimated.
The vibrational dependence of an interaction potential for a bending mode: NH3–He and the inversion motion
Authors: Davis Stephen L. , Boggs James E.
Published: February 2003

The electron gas interaction potential for the NH3–He system was calculated for five different NH3 C3v geometries. These geometries were chosen to lie along a one-dimensional minimum energy pathway for inversion, as parametrized by the Hartree–Fock calculations of Stevens. The inversion dependence of the interaction potential is well described by a second-order polynomial fit to the spherical harmonic expansion coefficients. The interaction potential was averaged over the vibrational motion in the ground state inversion doublets. The inversion motion is found to have a negligible effect on the ’’rigid-top’’ interaction potential.
A conjecture of nonphotochemical hole burning in organic glasses
Authors: Klafter Joseph , Silbey Robert
Published: February 2003

In this paper, a theory for the efficiency of nonphotochemical hole burning in organic glasses at 0 °K is presented. The dependence of this efficiency on the density of low energy modes in glasses is discussed.
The modified moment method and theory of nonlinear transport processes in gases: Third order cumulant approximation
Authors: Eu Byung Chan
Published: February 2003

By calculating the entropy production to the third order cumulant approximation within the framework of the modified moment method, we examine it for nonlinear transport processes and obtain nonlinear transport coefficients which include ’’Burnett-type’’ coefficients among them. The entropy production obtained has a mathematical form that can admit two minima, one at equilibrium and the other away from equilibrium. It therefore can have a region of decrease as the system is removed farther from equilibrium. This is a phenomenon not existent in linear theory or in the theory based on the first cumulant approximation in the modified moment method.
The influence of the permanent dipole and quadrupole moments in water on the thermodynamic characteristics of the hydrophobic effect
Authors: Goldman Saul
Published: February 2003

A thermodynamic perturbation theory that derives from the work of Gray, Gubbins, and Stell is used to analyze the influence of the permanent dipole and quadrupole moments in water on a variety of thermodynamic functions that characterize hydrophobic solvation and hydrophobic interactions. The model used for water was a generalized Stockmayer potential. Experimental values were used for the dipole moment and for the three components of the quadrupole tensor of water, and the parameters for the Lennard-Jones part of this potential were taken from Finney et al.’s polarizable electropole model for water. This potential function involves reduced dipole and quadrupole moments that are shown to be within the range of validity of Stell’s Padé approximant. Induced moments were not considered. The solute–solute and solute–solvent pair potential functions were taken to be the same as the Lennard-Jones part of the solvent–solvent pair potential function. The effects of three types of anisotropies, namely, dipole forces only, generalized quadrupole forces only, dipole–dipole plus generalized quadrupole–generalized quadrupole plus dipole–generalized quadrupole forces, are considered separately. Values obtained for the Henry’s law constant, the heat of solution, the partial molal volume, and the partial molal heat capacity, at infinite dilution, are compared with ranges of experimental values for these quantities for the rare gases in water. The closeness of our results to those data, for our solvent with all the anisotropies simultaneously turned on, is, with the exception of the partial molal volume, remarkable good. The reason for this one failure is discussed. Most surprising perhaps was the result, again for the solvent with the most complicated anisotropy, that it was possible, over a restricted temperature range, to mimic the drop in the osmotic second virial coefficient that is found in real aqueous systems at ordinary temperatures. A physical explanation for this behavior is given.
Variation of the rate of nucleation with supersaturation in a thermal diffusion cloud chamber
Authors: Flageollet-Daniel C. , Ehrhard P. , Mirabel P.
Published: February 2003

Thermal diffusion cloud chamber measurements of the homogeneous nucleation rate from the vapor of liquid ethanol has been made in order to test the ability of this sort of chamber to be used as a detector for photoinduced nucleation. The rates measured cover the range 1.0 to 2000 drops/cm3 sec at 297 °K. It is shown that very precise knowledge of the size of the droplets as a function of height in the chamber is necessary to obtain valuable information from the observed rates.
A torsional Fokker–Planck equation for butane
Authors: Evans Glenn T. , Knauss Donald C.
Published: February 2003

The torsional Fokker–Planck (TFP) equation for the single particle distribution function of the torsion (dihedral) angle and its angular velocity is derived for butane. Obtained is an equation which differs from the often used FP equation by the inclusion of extra streaming terms, a torsion angle dependent friction coefficient, and a contribution to the friction coefficient from the fluctuations in the inertia tensor.
Ultrasonic shear spectrum in hydrated diethylamine melanins and its relation to stacking in a planar group
Authors: Kono Ryusuke , Yoshizaki Haruyo , Miyake Yasuhiro , Izumi Yoshinobu , McGinness John E.
Published: February 2003

Shear mechanical relaxation and resonance data are reported for 20 wt % hydration of diethylamine melanins with different pH values ranging from 2 to 7. Shear impedance measurements in the temperature range from 60 to −80 °C, with frequencies from 1 to 362 MHz, indicate a Davidson–Cole spectrum in the primary relaxation and a single relaxation with a characteristic frequency of f = 4 MHz at 60 °C referred to the molecular motions of a group composed of an average molecular weight Mn?1.4×104. A resonance at 250 MHz is found in the specific melanin called No. 1, associated with stacking of indole monomer units, and a single relaxation at f = 270 MHz at 60 °C is found in the hydrate of melanin No. 2. The nature of the stacking is surveyed on account of Fitzgerald’s theory. The limiting shear modulus in the primary relaxation related to the molecular motion of backbone chains obeys the modified Hirai–Eyring equation. All the hydrations have an amorphous phase composed of a three-dimensional network structure.
Solvation forces in simple dense fluids. III. Monolayer and submonolayer region
Authors: Snook I. K. , van Megen W. J.
Published: February 2003

Solvation forces in simple dense fluids, monolayer and submonolayer region, is explored. (AIP)
Intermolecular potential energy function, second virial coefficients, and oligomer properties of hydrogen fluoride
Authors: Redington Richard L.
Published: February 2003

Six recently reported intermolecular potential energy functions for HF–HF interactions are examined and used to calculate classical second virial coefficient curves. Order of magnitude differences exist among the six B(T) curves and none of them decreases with temperature as rapidly as an experimental curve determined in the 19.5–56 °C range. The HF3 potential of Klein, McDonald, and O’Shea appears to give the best overall description of HF–HF interactions and this function is used to calculate properties of several higher (HF)q oligomers. The resulting low energy conformations are cyclic, and the hexamer has a puckered, nonrigid structure. The calculated hydrogen bond energies, F⋅⋅⋅F distances, and the puckered, nonrigid hexamer structure all agree well with the available experimental information.
Diffusion controlled reactions with interacting potentials: Comparison of boundary conditions and sink term methods
Authors: Perico A. , Battezzati M.
Published: February 2003

The two particle diffusion controlled reaction rate with Smoluchowski boundary conditions is derived by direct integration of the diffusion equation in the long time limit, together with an integral equation for the spatial part of the long time probability function. In a first order approximation this rate constant takes the value of the exact inverse mean first passage time. It is also shown how to obtain from the two particle result the rate constant for N concurrent independent two particle reactions between unbound particles. A new derivation is given of the mean first passage time in the Wilemski–Fixman closure approximation which clarifies the differences between the boundary conditions and sink term methods. Our previous statement that the exact and closure approximation results coincide to the third term of the expansion in the reaction sink radius is confirmed.
Adiabaticity and tunneling in quantal collinear reactive scattering computations
Authors: Pollak Eli
Published: February 2003

A classical prediction on the existence of adiabatic barriers even where no saddle point exists on the potential energy surface is verified using a purely quantal calculation. The adiabatic surfaces are then used for a vibrationally adiabatic transition state theory computation of reaction probabilities. Comparison with exact quantal results shows that the barriers suffice for explaining the so-called ’’dynamic barriers’’ to reaction. Since the barriers are in a region where the adiabatic assumption is valid, the adiabatic transition state theory provides an approximate upper bound to the exact reaction probabilities. Finally, it is shown that adiabatic transition state theory coupled with a purely classical transmission factor suffices for explaining most of the oscillatory nature of the exact quantal probability.
Calculation of integral cross sections for electronic excitation
Authors: Düren R. , Moritz G.
Published: February 2003

A method is presented to calculate the energy dependence of integral excitation cross sections for energies between 10 and 100 eV in the close coupling approximation. Especially the cross sections which are resolved with respect to the fine structure and the respective projection quantum numbers are obtained. The problem of the computing time for these systems has been solved by a Monte Carlo summation of the partial wave sum for the cross section. Results are presented for the alkali–mercury interaction.
The generator coordinate method applied to variational perturbation theory. Multipole polarizabilities, spectral sums, and dispersion coefficients for helium
Authors: Thakkar Ajit J.
Published: February 2003

It is shown that a suitable variant of the generator coordinate method can be used for accurate variational perturbation theory calculations. The test problems chosen are calculations of the dipole, quadrupole, and octupole polarizabilities, spectral sums, two-body dispersion coefficients, and nonadditive three-body dispersion coefficients for the ground state of atomic helium. An accurate explicitly correlated wave function for the unperturbed problem is utilized along with explicitly correlated basis functions for the pseudospectra. The dipole results are in excellent agreement with previous high accuracy calculations. The quadrupole and octupole results are expected to be the most accurate ones currently available. Estimates of some hexadecapole properties are made.
A microwave substitution structure for protonated nitrogen N2H+
Authors: Szanto Peter G. , Anderson Thomas G. , Saykally Richard J. , Piltch Nancy D. , Dixon Thomas A. , Woods R. Claude
Published: February 2003

Microwave observations of the J = 0–1 transitions of N2H+, 15N2H+,and 15N14ND+, N2D+, 15N2D+, and 15N14NH+ have been used to determine a substitution structure for N2H+. The resultant structural parameters are rs(NN) = 1.0947(4) Å and rs(NH) = 1.0320(1) Å, which agree beautifully with those from available ab initio calculations. The frequencies obtained for the 15N species provide a basis for their future radioastronomical detection and identification.
Infrared spectrum of H2O matrix isolated in CO at 10 K: Evidence for bifurcated dimers
Authors: Hagen W. , Tielens A. G. G. M.
Published: February 2003

The spectrum of H2O in a CO matrix is qualitatively different from that of H2O in other matrices. Not only are the frequency shifts of the monomeric absorptions with respect to the gas phase larger than in any other matrix, the pattern of the dimeric absorptions is also markedly different. It is concluded that the H2O dimer in a CO matrix has a bifurcated structure. A number of absorptions due to CO strongly interacting with H2O are also reported.
Laser induced fluorescence from the A 2Πi(v = 0) state of CO+
Authors: Katayama D. H. , Welsh J. A.
Published: February 2003

A pulsed, tunable dye laser is used to obtain either the excitation spectrum for the A 2Πi–X 2Σ+ (0,0) band of CO+, or the time resolved fluorescence from individual rotational levels of the upper state for this transition. The ions are formed by reacting CO with helium metastable atoms produced in a dc discharge. Although the rotational structure of the A 2Πi (v = 0) state is well known from numerous studies of the emission spectra of CO+, our laser excitation spectrum reveals perturbations in this state which have not been reported previously. ’’Extra’’ lines are observed in the R21 and Q22 branches of the A 2Π1/2–X 2Σ+ (0,0) sub-band and are associated with the e-parity rotational levels of the A 2Π1/2 spin component having J values of 2.5, 3.5, 4.5, 5.5, 6.5, and 7.5. The perturbing levels which are the source of these ’’extra’’ lines are the e parity or F1 spin components of the X 2Σ+(v = 10) state having the same J values. Perturbation matrix elements and wave function mixing fractions are determined from the experimental data. The molecular constants of the interacting states are deduced and a discussion is given on the effect of these perturbations on the time resolved fluorescence from individual rovibronic levels of the A 2Πi(v = 0) state.
Extrinsic carrier photogeneration in poly-N-vinylcarbazole. III. CT fluorescence quenching by an electric field
Authors: Yokoyama Masaaki , Shimokihara Shigeru , Matsubara Akitoshi , Mikawa Hiroshi
Published: February 2003

Field-induced CT fluorescence quenching has been observed in a poly-N-vinylcarbazole (PVCz) film doped with 1,2,4,5-tetracyanobenzene, which exhibits a large sensitized photocurrent in the corresponding CT absorption region. The CT fluorescence quenching is attributed to carrier photogeneration by the ’’field-assisted thermal dissociation’’ of an ion pair which has a higher excited CT state as precursor. The Onsager model for the dissociation of an ion pair satisfactorily explains the experimental data of the field and temperature dependences of the fluorescence quenching by an electric field. Combining previously proposed mechanism of extrinsic carrier photogeneration in the exciplex systems, a more general mechanism has been presented for extrinsic carrier photogeneration in solid-state, excited donor–acceptor systems.
Partitioning of electronic energy in NO collisions with a Ag(111) surface
Authors: Luntz A. C. , Kleyn A. W. , Auerbach D. J.
Published: February 2003

Partioning of electronic energy among the spin–orbit Λ-doublets states of NO scattered from a Ag(111) surface has been determined using laser-induced fluorescence. Non-Boltzmann partitioning is observed.
Photochemistry of the lowest excited singlet state: Acceleration of t
r
a
n
s–c
i
s isomerization by two consecutive picosecond pulses
Authors: Sumitani Minoru , Yoshihara Keitaro
Published: February 2003

The fluorescence lifetime of laser-excited trans-stilbene is studied as a function of temperature. (AIP)
On the monotonicity of atomic momentum densities and inequalities among atomic expectation values
Authors: Gadre Shridhar R. , Matcha Robert L.
Published: February 2003

Momentum densities for atoms with atomic numbers ranging from two to ten are calculated using various wave functions. The nature of momentum density functions is discussed in detail. (AIP)
Lightning rod effect in surface enhanced Raman scattering
Authors: Liao P. F. , Wokaun A.
Published: February 2003

The electromagnetic model of Gersten and Nitzan1 of the surface enhanced Raman scattering is discussed. The ’’lightning rod’’ effect is taken up in some detail. (AIP)
Beam maser spectroscopy on J = 1 → 2, K = 1, and K = 0 transitions in CH3CN and CH3 13CN
Authors: Kukolich Stephen G.
Published: February 2003

J = 1 → 2 transitions near 36.8 GHz in CH3CN and CH3 13CN were measured using a beam maser spectrometer. K = 1 transitions were observed with a 10 kHz linewidth (FWHM) and K = 0 transitions were observable with a two-cavity Ramsey system with about 3 kHz resolution. The measured difference between a axis and c axis nitrogen spin–rotation tensor components is Ca–Cc = 4.6±1.0 kHz for CH3CN and 4.5±1.0 kHz for CH3 13CN. The c axis nitrogen spin–rotation tensor component is Cc = 2.0±0.4 kHz. Nitrogen chemical shift tensor components of σa = 247 ppm and σc = −165 ppm are obtained from the data and calculated diamagnetic contributions. The measured paramagnetic contributions to the nitrogen chemical shift tensor are σap = −98±15 ppm and σcp = −600±120 ppm. Nitrogen quadrupole coupling strength is eqQ = −4224.3±4.0 kHz and rotational transition frequencies are: 36 795 476.9±3.0 kHz (CH3CN, K = 0), 36 794 769.3±1.5 kHz (CH3CN, K = 1), 36 777 282.6±3.4 kHz (CH3 13CN, K = 0), and 36 776 573.3±1.6 kHz (CH3 13CN, K = 1). This data, combined with previous J = 0 → 1 data yields accurate rotation and distortion constants for CH3CN and CH3 13CN as follows:
Proton NMR study of the orientation and motion of H2O in Na β′′ alumina
Authors: Kuhns Philip L. , Richter Lee J. , Conradi Mark S.
Published: February 2003

Proton NMR measurements in nearly dry Na β\ alumina crystals display a Pake doublet due to H2O molecules. At 300 K the angular dependence of the Pake splitting shows the time average orientation of the water HH vectors is parallel to the crystal c axis. Measurements at 133 K, where motional averaging is removed, demonstrate that HH is tilted from c by 5° to 13°. The frequency splitting of the doublet shows that the HH distance is between 1.65 and 1.71 Å, longer than in free H2O. Above 250 K, line narrowing indicates the H2O are translationally diffusing while maintaining their orientation. A model of this motion is suggested. The chemical shift anisotropy of the H2O is found to be in agreement with previous measurements of H2O in ice and gypsum.
The relative energies of SF−6 and SF6 as a function of geometry
Authors: Hay P. Jeffrey
Published: February 2003

The potential curves as a function of symmetric stretch have been computed for SF6 and SF−6 at the SCF level. The calculated electron affinity of 0.90–1.00 eV and the photodetachment threshold of 3.0 eV appear to be in good agreement with existing experimental data.
Local behavior of the Clementi–Roetti atomic Hartree–Fock wave functions. Improved local accuracy using global constraints
Authors: King Frederick W. , Kelly Michael K. , LeGore Mary A.
Published: February 2003

The reduced local Hartree–Fock energy for the neutral atoms Li through to Al have been calculated using the Hartree–Fock wave functions of Clementi and Roetti. These wave functions were found to give rather accurate values of the reduced local energy in the medium range region (r values 1∼12 a.u.9), but inaccurate values close to the nucleus. The reduced local energy was found in each case to exhibit oscillations about the ’’exact’’ total Hartree–Fock energy as a function of the configuration space coordinate r, indicating some cancellation of opposing errors in the wave functions used for the calculation of the total energy. A method is outlined for determining Hartree–Fock wave functions which not only satisfy the customary condition that the total energy be minimized, but in addition, are locally accurate. The criterion which is used to monitor the local accuracy is the reduced local energy. The reduced local energy is incorporated into a global accuracy constraint on the wave function, and the energy is determined subject to the minimization of this additional constraint. Calculations are performed for various helium wave functions. The five-term Clementi–Roetti wave function is refined, maintaining essentially the same total energy, but with considerable improvement in local accuracy. The Clementi (1965) wave function for helium is also refined. A ten-term function for helium is devised which has improved accuracy at the local level. Comparison of expectation values of r1k using the different wave functions is made, in order to assess the utility of the reduced local energy as a criterion for refinement of such values.
Study of the correlated walks with reflecting walls
Authors: Okamura Y. , Blaisten-Barojas E. , Godoy S. V. , Ulloa S. E. , Fujita S.
Published: February 2003

Exact expressions for the arrival probabilities with direction are obtained for correlated walks on an infinite line. The probability distribution exhibits a diffusive maximum, similar to that characteristic of random walks, and a runaway component which is associated with free passage (no scattering). For symmetric step probabilities, the arrival probabilities for a finite line bounded by reflecting walls are expressible in terms of free-space probabilities. The evolution of the system of probabilities is studied in terms of the Boltzmann H function. The system approaches equilibrium monotonically. In general, there exists an optimum degree of correlation between successive steps at which the randomization in space and direction proceeds most rapidly. At lower correlation the system moves like a wave packet with dissipation. The randomization in space is aided by the reflecting walls (and by the periodic boundary).
Transient features of optical bleaching as studied by photochemical hole burning and fluorescence line narrowing
Authors: Friedrich J. , Haarer D.
Published: February 2003

This paper presents various laser excitation experiments on matrix-isolated 1,4-dihydroxyanthraquinone (DAQ). The molecular spectra are studied in two different organic glasses, namely a hydrogen-bonding matrix of 3:1 EtOH/MeOH and a nonhydrogen-bonding matrix of 3-Me-pentane. The experimental techniques are photochemical hole burning (PHB) and fluorescence line narrowing (FLN). The main difference between the two organic glass matrices is the host-induced photoreactivity of DAQ in the alcohol matrix and the photostability of DAQ in the pentane matrix. This difference leads to ’’anomalous’’ spectral features in the photoreactive alcohol–DAQ system. In this system, the zero-phonon transition appears to be more intense at higher temperatures, contrary to the well-proven theories on electron–phonon coupling. The unusual spectral line shapes are explained as transient features due to the efficient photochemistry of DAQ in hydrogen-bonding matrices.
Tests of effective pair potentials for water: Predicted ice structures
Authors: Morse Michael D. , Rice Stuart A.
Published: February 2003

As a test of the accuracy of the several proposed effective pair potentials for water, we have examined how well they reproduce the structures and properties of the proton-ordered ices II, VIII, and IX, and those of a hypothetical proton ordered form of ice I which is closely related to ice Ih. Despite leading to a consistent underestimate of all the ice densities by roughly 21%, the ab initio pair potential calculated by Matsuoka, Clementi, and Yoshimine succeeds better than any other in predicting the hydrogen bonding topology and the O–O–O angles characteristic of the various ice lattices. Some of the proposed water–water potentials predict the existence of ice polymorphs entirely different from known forms of ice, and/or give rise to structures with bifurcated hydrogen bonds. Using our new results, and others in the literature, we give a detailed discussion of the features of the MCY, ST2, and RSL2 potentials, each considered a representative of a class of potentials.
Hole burning into velocity distribution of thermal electrons due to resonance attachment to O2
Authors: Koura Katsuhisa
Published: February 2003

The hole burning into the velocity distribution of thermal electrons due to the resonance attachment to O2 in pure O2 is studied using the Monte Carlo simulation. The thermal molecular motion, which dominates the electron velocity range for the resonance attachment, plays an important role in the hole burning process. The attachment hole without the autodetachment filling effect (the upper limit of hole size) is burned at the lower temperature T≲100 °K and becomes deeper and narrower with decreasing T owing to the decrease in the thermal molecular motion. Since the attachment hole is not burned in pure O2 at room temperature owing to the thermal molecular motion, the attachment rate constant for e+O2→O2−* measured by Shimamori and Hatano in binary gas mixtures at room temperature does not suffer the attachment cooling effect indicated by Crompton et al.
Dissociative photoionization cross sections of O2 from threshold to 120 Å
Authors: Samson James A. R. , Rayborn Grayson H. , Pareek P. N.
Published: February 2003

The photoionization cross sections for producing the O2+ parent ion and the O+ fragment ion from neutral O2 are presented from 650 to 120 Å. A new technique was used that eliminated the serious problem of identifying the true abundance of the O+ ions. These ions are generally formed with considerable kinetic energy and because most mass spectrometers discriminate against energetic ions true O+ abundances are difficult to obtain. In the present work the relative cross sections for producing O2+ are obtained and normalized against the total cross sections in a spectral region where dissociative ionization is not possible. The fragmentation cross sections for O+ were then obtained by subtraction of the O2+ cross section from the total photoionization cross section.
EPR investigations of Fe3+ in single crystals and powders of the zircon-structure orthophosphates LuPO4, YPO4, and ScPO4
Authors: Rappaz M. , Ramey J. O. , Boatner L. A. , Abraham M. M.
Published: February 2003

Iron-doped single crystals of the zircon-structure orthophosphates LuPO4, YPO4, and ScPO4 have been grown by means of a flux technique. Corresponding powders have been prepared independently by a urea precipitation technique and electron paramagnetic resonance measurements demonstrate that the Fe3+ impurity is situated in the same substitutional site in both the single crystals and the powders for all three hosts. The sign of the crystal field parameter b02 is shown to be positive (opposite to that found for Gd3+ in these hosts). The crystal-field splittings were found to be largest for the scandium host and smallest for the yttrium host. The EPR results show that iron can be incorporated in a substitutional crystallographic site in material prepared by either a high temperature process or by a low temperature precipitation and calcination (∼800 °C), and these findings have implications for the use of lanthanide and related orthophosphates as a host material for the isolation of nuclear wastes.
Second-order electron correlation energies for Zn2+ and Zn
Authors: Jankowski K. , Malinowski P. , Polasik M.
Published: February 2003

Second-order Rayleigh–Schrödinger Hartree-Fock perturbation theory is applied for an extensive study of the correlation energies of Zn2+ and Zn in order to analyze the nature of various correlation effects. The variational–perturbation method is based on the application of symmetry-adapted pair functions taken in the form of partial-wave (PW) expansions. The partial-wave energy increments, pair energies, and total second-order correlation energies E2 are calculated using extended radial basis sets. Special attention is paid both to the M and N intrashell and to the LM, LN, and MN intershell correlation effects. For every pair of the system all PW’s up to l′, l′′?9 are considered. Extrapolation of the pair energies for l′, l′′≳9 results in total second-order energies EZn2+2 = −1.604 16 and EZn2 = −1.698 69 hartree. The systems considered, which contain the 3d10 and 3d104s2 electron configurations, are the largest for which a complete analysis of the correlation effects has been attempted by ’’ab initio’’ methods. The complicated structure of the systems offers the possibility of investigating various aspects of the electron correlation problem. The results confirm the suggestions made by Clementi [J. Chem. Phys. 42, 2783 (1965)] that for the outer shells of large atoms one is approaching the situation when a ’’complex pairing model’’ has to be used in place of the ’’simple pairing model’’ based on the notion of weak and strong electron pairs. Comparison with other related work is given.
van der Waals coefficient between closed shell ions
Authors: Mahan G. D.
Published: February 2003

The van der Waals force coefficient C6 is calculated between all pairs of fourteen different ions. The density functional method is used. The few cases which can be compared with other methods are in good agreement.
Spectroscopy and triplet state lifetime for yttrium fluoride (YF) in inert gas matrices
Authors: Hamilton C. E. , Lesiecki M. L. , Allamandola L. J. , Nibler J. W.
Published: February 2003

Absorption and emission spectra are reported for YF isolated in Ne, Ar, and Kr matrices and the ground state is confirmed as 1Σ+. Calculated Franck–Condon intensities permit confident assignments of vibrational quantum numbers for most of the states but point to an anomaly in the red emission produced on excitation into the B̃ state. Lifetime studies in argon show that such excitation also depletes ∼90% of the ground state population and that the return requires ∼15 min. As explanation, the ã 3Δ state of YF is proposed as a metastable sink, with the longest lifetime yet reported for a triplet state in matrices. Evidence for direct b̃ 3φ←X̃ 1Σ+ absorption is also presented and this suggests that the ã 3Δ state lies within ∼200 cm−1 of the X̃ state. The lifetime of the ã state is a sensitive probe of coupling of YF to the lattice phonons and it decreases by four orders of magnitude for YF in neon and in a ’’tighter’’ second site in argon.
Resonance Raman scattering by a predissociative state: A study of nonadiabatic effects
Authors: Bandrauk André D. , Turcotte Gilles , Lefebvre Roland
Published: February 2003

A coupled equation approach is used to study the excitation profiles of the resonant Raman scattering of a predissociative electronic state in a diatomic molecule. The method allows one to calculate also the photopredissociation cross section so that a comparison between the two processes can be made. Calculations are presented for a realistic system, the scattering from the predissociated B 3Π0+ state of IBr.
Lifetime lengthening through rotational coupling: Decay in the 1B1g and 1A
u states of para-benzoquinone
Authors: ter Horst Gerard , Kommandeur Jan
Published: February 2003

The lower excitations in the B1g and Au singlet states of para-benzoquinone correspond to the small molecule limit. Stern–Volmer type experiments in a supersonic jet have given the collision-free lifetimes of these states. These lifetimes increase with increasing rotation, which is due to the increased (Coriolis) coupling with the background manifold. Values for the vibronic and Coriolis coupling parameters can be extracted from the data. It then becomes evident that at about 2000 cm−1 above the origin the rotational effects are masked by the singlet–triplet radiationless decay, and indeed above that energy no rotational effects are observed.
Resonance absorption measurements of atom concentrations in reacting gas mixtures. VIII. Rate constants for O+H2→OH+H and O+D2→OD+D from measurements of O atoms in oxidation of H2 and D2 by N2O
Authors: Pamidimukkala Krishna M. , Skinner Gordon B.
Published: February 2003

Resonance absorption spectroscopy has been used to measure O atom concentration in shock treated H2–N2O–Ar and D2–N2O–Ar mixtures. Four compositions were studied over the temperature range 1919–2781 K for the H2-containing mixtures and 2097–2481 K for those containing D2. Only a few elementary reactions exerted any appreciable influence on the total oxidation process so that the rate coefficients of those reactions could be deduced. Primary sensitivity under all conditions was to the rate coefficients of the reactions directly responsible for the formation and removal of oxygen atoms. We find O+H2→OH+H, k = 2.3E14 exp(−57.5 kJ/RT) cm3 mol−1 s−1 and O+D2→OD+D, k = 1.6E14 exp(−59.6 kJ/RT) cm3 mol−1 s−1. Under our conditions the reaction of H or D atoms with N2O was insignificant, in contrast to the observations of Dean at higher concentrations. The isotope effect for this reaction is close to 1.6 throughout our temperature range.
Intramolecular dynamics by photoelectron spectroscopy. I. Application to N+2, HBr+, and HCN+
Authors: Lorquet A. J. , Lorquet J. C. , Delwiche J. , Hubin-Franskin M. J.
Published: February 2003

The Fourier transform of an optical electronic spectrum leads to an autocorrelation function C(t) which describes the evolution in time of the wave packet created by the Franck–Condon transition, as it propagates on the potential energy surface of the electronic upper state. This correlation function is equal to the modulus of the overlap integral between the initial position of the wave packet and its instantaneous position at time. The original data resulting from an experimentally determined spectral profile must be corrected for finite energy resolution, rotational, and spin-orbit effects. The behavior of the system can then be followed up to a time of the order of 10−13 s, i.e., during the first few vibrations which follow immediately the electronic transition. The method is applied to photoelectron spectra and the results are compared to the available information on potential energy surfaces of ionized molecules, in order to study their unimolecular dissociation dynamics. In the case of the X 2Σ+g, A 2Πu, and B 2Σ+u states of N+2, an oscillatory pattern is obtained for the correlation function. This indicates that the nuclear motion is taking place in a bound potential. Effects due to anharmonicity are visible in the case of the A 2Πu state. The study of the X 2Π state of HBr+ demonstrates the overwhelming importance of spin-orbit coupling when heavy atoms are present in the molecule. Finally, the method is applied to a polyatomic molecule. The potential energy surface of the ? 2Σ+ state of HCN+ is characterized by two energy minima separated by a saddle point. The corresponding band in the photoelectron spectrum is characterized by an irregular vibrational structure superimposed upon a broad continuum. A study of the correlation function shows that the wave packet undergoes a complicated, two-component motion: while oscillating across the saddle point, it spreads away at the same time along the dissociative degree of freedom. This gives information on the rate of energy redistribution within the molecule.
Transition strengths in the visible–infrared absorption spectrum of I2
Authors: Tellinghuisen Joel
Published: February 2003

The contributions of the 1Πu←X, B←X, and A←X transitions to the absorption coefficient of I2 in the 4200–8000 Å region are reassessed in light of recent results concerning the 1Πu and A potentials and their diffuse absorption spectra. Earlier estimates of the continuum underlying the B←X discrete spectrum are augmented by additional high-resolution ’’between-the-lines’’ absorption measurements, corrected for residual B–X absorption using the very reliable spectroscopic constants now available for this system. The 1Πu–X and A–X systems are now estimated to be about 10% weaker than in the previous analysis [J. Tellinghuisen J. Chem. Phys. 58, 2821 (1973)]. For the region 2.6–2.8 Å sampled in absorption, the estimates of the B–X transition strength ‖μe‖2 remain close to the previous values.
Optical spectra, energy levels, and crystal-field analysis of tripositive rare-earth ions in Y2O3. II. Non-Kramers ions in C2 sites
Authors: Leavitt Richard P. , Gruber John B. , Chang N. C. , Morrison Clyde A.
Published: February 2003

Optical absorption and fluorescence spectra of the non-Kramers ions Pr3+, Tb3+, and Ho3+ in the C2 sites of Y2O3 are reported. A crystal-field analysis of these data and previously reported data for Eu3+ and Tm3+ is performed that is based on a Hamiltonian of C2 point-group symmetry, including J-mixing effects. A best-fit analysis is performed for all five ions; resulting rms deviations between calculated and experimental levels range from 2.8 to 26.4 cm−1. Results of this analysis and of our previous analysis of Kramers ions in C2 sites are used to obtain a set of phenomenological crystal-field components Akm for the C2 sites. We predict the crystal-field splittings for Pm3+ in Y2O3, and we compare our previous prediction of the splittings of Gd3+ in Y2O3 with recently reported measurements. We also describe an effective point-charge model for the Y2O3 lattice in which good agreement between calculated and phenomenological Akm is obtained with qY1 = 2.53, qY2 = 1.26, and q0 = −1.052. (The quantities qY1, qY2, and q0, are, respectively, the charges on the C3i yttrium site, the C2 yttrium site, and the oxygen site, in units of e.) With this model, we calculate Akm for the C3i sites.
Vibronic analysis of circular dichroism spectra of dimeric systems. Chiral molecules consisting of two polyacene chromophores
Authors: Pawlikowski M. , Zgierski M. Z.
Published: February 2003

The CD spectra of (6R,15R)-(+)-6,15-dihydro-6,15-ethanonaphtho [2,3-c]pentaphene (DEP) and (7R,14R)-(+)-7,14-dihydro-7,14-ethanondibenz [a,h] anthracene (DEA) are analyzed as dimers of anthracene and naphthalene, respectively. It is shown that vibronic coupling effects are essential in understanding the vibronic structure of CD spectra in these molecules. The simple molecular dimer model is shown to explain the main vibronic features of the CD spectra, but an extension of that model is needed to achieve good quantitative agreement between experimental and theoretical CD spectra for physically reasonable exciton and vibronic coupling parameters. This extended dimer model allows for a mixing of electronic states of monomers via electronic intermonomer interaction. It is shown that the CD spectrum of DEP locates the hidden 1Lb state of the anthracene molecule about 2150 cm−1 above the origin of the 1La state, and that these two states are electronically coupled in DEP. Only these two assumptions taken together can well explain the CD and absorption spectra of DEP for the same set of parameters. We show that the CD spectra of DEA indicate strong mixing of the 1Lb and 1Bb and of the 1Bb and 1Cb states of naphthalene molecule via intermonomer interaction. The calculations presented here point out that the main reasons of previous failure to explain the vibronic structure of the CD spectra of DEP and DEA is the brakedown of the Born–Oppenheimer approximation in these dimers.
An infrared study of the dynamics of weakly bound water in crystalline hydrates
Authors: Corn Robert M. , Strauss Herbert L.
Published: February 2003

Isotopic dilution studies of water molecules in weakly bound crystalline hydrates reveal a strong dependence of the infrared spectra on temperature. The infrared stretching and bending bands of dilute HDO in NaClO4⋅H2O and LiI⋅3H2O show multiple bands at low temperature which broaden and move together as the temperature is raised. In contrast, only single narrow bands are seen in the very similar LiClO4⋅3H2O. The potential in which the waters move is calculated from a simple electrostatic model. The stretching frequencies are taken to be a function of the librational coordinate of the water and the observed frequencies are then averages over the libration. This simple prescription for calculating the observed bands is that given by Redfield theory. We conclude that the observed band collapse in NaClO4⋅H2O is due primarily to the increase with temperature of the in-plane water libration. At higher temperatures, the 180° flipping motion also contributes to the collapse. For LiI⋅3H2O, the motion is a complex one involving locally ordered domains of the water molecules in the crystal.
Brillouin light scattering studies of structural relaxation in 1,5- and 2,4-pentanediol
Authors: Lempert W. , Wang C. H. , Fytas G. , Dorfmüller Th.
Published: February 2003

The basic assumptions which were made in the development of the theory of Brillouin light scattering of viscoelastic liquids by Lin and Wang have been tested using the new experimental data obtained for 2.4- and 1,5-pentanediol. The comparison between the theory and experiment deals with the spectral line shape and the intensity. The results show that the Arrhenius temperature dependence assumed for the structural relaxation time is realistic, whereas the assumption about the linear temperature dependence for the adiabatic hypersonic frequency (ωs) is not always valid. Angular dependence studies have shown that τs is independent of the scattering angle, consistent with the assumption that the structural relaxation arises from the local fluctuation processes. The comparison between theory and the experimental data also yields the proper angular dependences expected for the relaxation strength and the adiabatic hypersonic frequency. The activation energies obtained are related to the results obtained from other techniques.
On the relation between nucleation work, nucleus size, and nucleation rate
Authors: Kashchiev Dimo
Published: February 2003

A general thermodynamic relation is proved to exist between the nucleation work and the nucleus size regardless of the model for the excess free energy of the nucleus. When this energy is supersaturation independent, the relation reads as follows: the number of atoms (or molecules) in the nucleus equals the derivative with minus sign of the nucleation work with respect to the supersaturation Δμ. It is shown that, experimentally, a reliable determination of the nucleus size is possible when data for the stationary nucleation rate J are plotted in coordinates kT ln J vs. Δμ (k is the Boltzmann constant and T is the absolute temperature). The slope of such an experimental curve gives information about the nucleus size independently of the kind of nucleation: classical or atomistic, homogeneous or heterogeneous, three dimensional or two dimensional, etc.