bluuebunny/crossref_metadata_2025 huggingface dataset:
Exact classical scaling formalism for nonreactive processes
Authors: DePristo Andrew E.
Published: February 2003

A general nonreactive collision system is considered with internal molecular variables (p, r) and/or (I, ϑ) of arbitrary dimensions and relative translational variables (P, R) of three or less dimensions. We derive an exact classical scaling formalism which relates the collisional change in any function of molecular variables directly to the initial values of these variables. The collision dynamics is then described by an explicit function of the initial point in the internal molecular phase space, for a fixed point in the relative translational phase space. In other words, the systematic variation of the internal molecular properties (e.g., actions and average internal kinetic energies) is given as a function of the initial internal action-angle variables. A simple three term approximation to the exact formalism is derived, the natural variables of which are the internal action I and internal linear momenta p. For the final average internal kinetic energies T̄, the result is T̄−T̄(0) = α+βp(0)+γI(0), where the superscripted ’’0’’ indicates the initial value. The parameters α, β, and γ in this scaling theory are directly related to the moments of the change in average internal kinetic energy. Utilizing a very limited number of input moments generated from classical trajectory calculations, the scaling can be used to predict the entire distribution of final internal variables as a function of initial internal actions and linear momenta. Initial examples for atom–collinear harmonic oscillator collision systems are presented in detail, with the scaling predictions (e.g., moments and quasiclassical histogram transition probabilities) being generally very good to excellent quantitatively.
Coulomb holes and correlation coefficients for electronic shells: A comparative analysis of several wave functions for Be
Authors: Banyard K. E. , Mobbs R. J.
Published: February 2003

A partitioning technique used previously to examine correlation trends in individual electronic shells for a series of ions has been extended and applied to a detailed comparison of four well-correlated wave functions for the Be atom. The present analysis of a correlated two-particle density, generalized for any N-electron system, retained all contributions from products of all terms in the wave function up to and including the pair-correlation effects. For each correlated description of Be, Coulomb holes have been evaluated and compared for the K(1S), L(1S), KL(1S), and KL(3S) shells. The inverted nature of the inter-shell holes, relative to the intra-shell effect, has been examined and rationalized in terms of the 2s–2p near-degeneracy which exists in Be. The total Coulomb holes for the two energetically best wave functions showed a previously unseen structure which was directly attributable to the inter-shells. Several one- and two-particle expectation values are reported and these were used to determine various angular and radial correlation coefficients τ. Thus, for each wave function, a global assessment could be obtained of the correlation effects within different regions of the intra- and inter-electronic shells.
Valence correlation in the s2d
n, s
d
n+1, and d
n+2 states of the first-row transition metal atoms
Authors: Botch Beatrice H. , Dunning Thom. H. , Harrison James F.
Published: February 2003

The major differential valence correlation effects of the lowest lying states arising from the s2dn, sdn+1, and dn+2 configurations of the first-row transition metal atoms have been characterized using MCSCF and CI procedures. The important correlation effects are found to be, first, angular correlation of the 4s2 pair arising because of the near degeneracy of the 4s and 4p orbitals and, second, radial correlation of the 3d electron pairs. This large differential radial correlation of the 3d electrons can be interpreted as being due to nonequivalent d orbitals in the sdn+1 and dn+2 excited states. Both of these effects can be incorporated into a simple MCSCF wave function that reduces the error in the excited state atomic dissociation limits (∼0.2 eV in Sc–Cr and ∼0.5 eV in Mn–Cu for the sdn+1–s2dn excitation energy), yet still is of a form which lends itself easily to molecular calculations.
Existence of the dielectric constant in dipolar fluid mixtures
Authors: Ramshaw John D. , Hamer Norman D.
Published: February 2003

The existence of the dielectric constant ε is investigated for fluid mixtures of rigid polar molecules. The investigation is performed using the functional-derivative formalism for mixtures, and is closely analogous to that previously carried out for pure dipolar fluids [J. Chem. Phys. 68, 5199 (1978)]. Sufficient conditions for the existence of ε are obtained in terms of the direct correlation function matrix cαβ(12). It is found that ε exists if cαβ(12) depends only on relative positions and orientations, and becomes asymptotic to −ϑαβ(12)/kT at long range, where ϑαβ(12) is the dipole–dipole potential between a molecule of species α and one of species β. An expression for ε in terms of the short-range total correlation function matrix emerges automatically from the development. This expression is equivalent to an earlier result obtained by a different method. Expressions for ε in terms of cαβ(12) are derived for axially symmetric molecules and for molecules of arbitrary symmetry. In the former case, the expression involves the inverse of an Nc×Nc matrix, where Nc is the number of components in the mixture. This expression facilitates the evaluation of ε in the mean spherical approximation. For molecules of arbitrary symmetry, the expression for ε in terms of cαβ(12) involves the inverse of an Nc×Nc supermatrix, each element of which is a 3×3 matrix.
The equation of state for nematics revisited
Authors: Flapper S. D. P. , Vertogen G.
Published: February 2003

A phenomenological equation of state for nematics is proposed. The starting point is a simple relation between the packing fraction and the excluded volume of two molecules. In addition, isotropic and anisotropic attractive forces are taken into account. The interactions are treated in the mean field approximation and the calculations are compared with the experimental data for a number of nematics including two homologous series. The results for PAA are also compared with previous theoretical results. Reasonable agreement with experimental data is obtained for all nematics considered. However, a physically relevant description of the mutual differences between nematics does not appear to be possible. Suggestions for improvement are made.
Characteristics of low resolution Q-branch microwave bands: Applications to 2,2,2-trifluoroethyl vinyl ether and 7-methylbicyclo[2.2.1]-hept-2-ene-5-one
Authors: Dennison F. T. , Gillies C. W. , Borchert S. J.
Published: February 2003

A rigid rotor analysis of μb- and μc-type Q-branch series indicates overlapping low J transitions giving rise to the low resolution microwave bands which follow a half-integer frequency rule. At higher J values certain Q-branch series form bandheads shifted to a lower frequency from the series origin. Under favorable circumstances low resolution bands are expected and the frequency of these bands may be used to estimate the rotational constant parameter (A−C). The microwave spectrum of 2,2,2-trifluoroethyl vinyl ether exhibits bands which are assigned to the bandhead phenomenon. This provides a value of (A−C) and in conjunction with previous data yields the three rotational constants A, B, and C uniquely from low resolution data. The results are consistent with the s-cis-planar as well as gauche conformations. Previously reported low resolution bands of 7-methylbicyclo[2.2.1]-hept-2-ene-5-one are interpreted as two half-integer band series arising from low-lying vibrational states with slightly different values of (2A−B−C).
Density dependence of the light scattering spectrum of fluid nitrogen
Authors: Medina F. D. , Dugas J. M.
Published: February 2003

The light scattering spectrum of fluid nitrogen at 157 K and densities between 120 and 462 amagat was fitted to a third order virial expansion in the density. The one-body intensity contains the unresolved rotational spectrum of the isolated molecules. The two-body intensity contains a rotation–collision cross contribution with a zero integrated intensity, as expected, and a purely collision-induced contribution with the exponential form and decay constant predicted by the model of Bucaro and Litovitz. This latter contribution, unlike all systems previously studied, was found to be negative. The three-body intensity is positive with a shape similar to that of the two-body intensity.
Location and movement on dehydration of Cu2+ in Cs7Na5A zeolite from electron spin echo modulation analysis
Authors: Narayana M. , Kevan Larry
Published: February 2003

It is shown that paramagnetic ions like Cu2+ can be located and that their motion upon dehydration in zeolites can be monitored by electron spin echo modulation analysis. In Cs7Na5A zeolite, Cu2+ is located inside the β cage about 0.1 nm below a hexagonal window between the β and α cages. The Cu2+ is coordinated to three lattice oxygens and one water molecule. On dehydration Cu2+ moves out of the β cage along the threefold axis of the hexagonal window to about 0.1 nm above the hexagonal window into the α cage.
A unitary approximation to the inelastic binary collision problem
Authors: Turner R. E. , Dahler J. S.
Published: February 2003

The memory function formulation of the time-dependent Schrödinger equation is used to analyze the internal state problem associated with the decoupled motions or impact parameter approximation to binary collisional events. The exact, time-orderd memory functions are then replaced with their time-disordered counterparts. This generates a unitary approximation to the collision problem as well as simple, easily interpretable formulas for the transition probabilities. Two specific examples are considered in detail, namely, (i) the three-state resonant transfer model and (ii) a ’’paired-states’’ model for the dynamics of a many-state problem.
Reactions of the HnS+ ions (n = 0 to 3) with several molecular gases at thermal energies
Authors: Smith David , Adams Nigel G. , Lindinger Werner
Published: February 2003

The rate coefficients and product ion distributions have been determined at room temperature for the reactions of the ions HnS+ (n = 0 to 3) with several diatomic and polyatomic gases. The reactions generally proceed at or near the collisional limit, often generating multiple products. Charge transfer, proton transfer, and atom abstraction, in some cases occurring in parallel, are evident within the data array, emphasizing the complexity of these reactions. The results obtained for the near-thermoneutral reactions of S+ and HS+ with H2S have provided values for the recombination energies of HS+ and H2S+ ions which, within the limitations of the assumptions made, are more closely defined than the previous values.
Isomerization and n-type doping of polyacetylene: Pure t
r
a
n
s-(CH)x and t
r
a
n
s-(CD)x
Authors: Francois B. , Bernard M. , Andre J. J.
Published: February 2003

A systematic study of thermal isomerization leads to a definition of standard conditions (5 min at 180 °C) to obtain trans-polyacetylene (CH)x and (CD)x. Light doping with Na derivatives of benzophenone enables the preparation of pure trans-(CH)x and (CD)x. The characteristics of these systems have been determined and, in particular, a peak-to-peak ESR linewidth as small as 0.28 G has been found for both systems. ESR and IR spectroscopic evidences of the inhomogeneity of the doping process have been obtained. The dopant is concentrated at the surface before penetrating inside the fibrils. The doping process is linked to the appearance of additional bands in the IR spectra, the position of which is sensitive to the nature of the polymer [(CH)x or (CD)x] and of the doping agent (Na or I2). Upon ’’compensation’’ by a subsequent doping, the properties of the insulating trans-(CH)x are recovered, but any doping inside the fibers is proved to create a high concentration of magnetic defects. After such compensation, a further doping allows recovery of the metallic state.
Spectroscopic examination of a
b i
n
i
t
i
o neon diatom polarizability invariants
Authors: Dacre Peter D. , Frommhold Lothar
Published: February 2003

Neon diatom polarizability is spectroscopically examined. (AIP)
On the stability criteria of the Kirkwood–Riseman diffusion tensor
Authors: Armstrong R. C. , Jhon Myung S.
Published: February 2003

A convincing prrof of the positive definite property of an altered form of the Kirkwood–Riseman diffusion tensor is provided by excluding the nonphysical singularities. (AIP)
Two-photon spectroscopy in HF
Authors: Carter Gary M.
Published: February 2003

By using two-photon absorption spectroscopy, rotational relaxation in a low pressure HF gas is investigated. The relaxation rate for the J = 5 rotational level of the v = 2 vibrational state was found to be 15±3 MHz/Torr. The pressure broadening coefficients for the two-photon transition (v = 0,J = 7) to (v = 2,J = 5) and the single-photon P2(6) transition were found to be 11.5± and 10±2 MHz/Torr, respectively. Included is a discussion of extending the technique to study elastic and velocity-changing collisions between HF molecules and rare gas atoms.
Semiempirical calculation of diamagnetic susceptibilities of organosilicon compounds containing Si–X (X = O, S, and N) bonds
Authors: Gupta R. R. , Kumar M. , Ojha K. G.
Published: February 2003

A semiempirical model is reported to calculate diamagnetic susceptibilities of organosilicon compounds containing silicon–oxygen, silicon–sulfur and silicon–nitrogen bonds. The diamagmetic susceptibilities are considered to be contributed by the atoms, bonds, and bond–bond interactions. Diamagnetic susceptibilities are expressed in terms of parameters and have been calculated for title compounds. Semiemperical values agree with experimental values within 0.75%.
Vibronic origin of satellites in photoelectron spectra and magnetic properties of transition metal complexes
Authors: Fukumi Toshio
Published: February 2003

Satellites in x-ray photoelectron spectra are shown to arise from simultaneous excitation of vibronic levels of outer-shell electrons accompanying photoionization in which the dynamic Jahn–Teller effect plays a role in splitting the degenerated outer-shell electron levels. An attempt is made to correlate the splitting of photoelectron spectra to the magnetic properties of transition metal complexes in terms of Jahn–Teller distortion of the ligand field.
An electron spin double resonance study of x-ray irradiated phenacyl chloride single crystals
Authors: Hwang J. S. , Wang H. C. , Andersson B. , Kispert L. D. , Geoffroy M.
Published: February 2003

Single crystals of phenacyl chloride irradiated at room temperature give rise to an EPR spectrum that has been shown by ENDOR and ELDOR studies to be due to the radical The EPR spectra are complicated by the appearance of a large number of forbidden lines due to the presence of a chlorine quadrupole interaction similar in magnitude to the proton hyperfine coupling. Spectral assignment is not possible by considering the EPR spectra alone. Although ENDOR spectra are difficult to obtain, it is possible to obtain an ENDOR spectrum along one of the crystal axis that identifies the spectra as due to radical I. Furthermore, rather intense and highly resolved ELDOR spectra are obtained at −60 °C as a function of angle enabling the chlorine and proton magnetic hyperfine tensor components of the –ĊHCl fragment to be determined as −15.4, −8.3, +45.6 MHz and −26.5, −52.5, −80.0 MHz, respectively. The Qzz components of the chlorine quadrupole tensor is −11.2 MHz.
The determination of the site-energy distribution of organic molecules dissolved in glassy matrices
Authors: Fünfschilling J. , Zschokke-Gränacher I. , Williams D. F.
Published: February 2003

We present a method that allows the determination of the distribution of 0–0 energies of organic molecules in glassy matrices. Starting with the assumption that the spectra of differently sited molecules in the glass have different origins but are otherwise identical, we develop an algorithm that allows the decomposition of the observed spectra into the contributions from the different sites and thus eliminate the strong inhomogeneous broadening which occurs in glassy matrices. The input data for our algorithm are site selection spectra excited at different energies. These spectra have been measured for the phosphorescence of 1-iodonaphthalene in bromobutane. The resulting site distribution has a Gaussian shape with a width of 190 cm−1. The simple theory developed is found to predict the observed shape and intensity measured for the phonon wing of the 0–0 transition for different excitation energies.
Decay and buildup characteristics of delayed luminescence in a ’’real’’ organic mixed crystal: Naphthalene host–chrysene guest system
Authors: Talapatra Gautam Buddha , Misra T. N.
Published: February 2003

The decay and the buildup characteristics of delayed emissions in a naphthalene host–chrysene guest ’’real’’ four component mixed crystal consisting of the host, a physical defect, the guest, and a chemical impurity have been studied. Heterofusion of the defect–guest and the defect–impurity triplet excitions have been found to be responsible, respectively, for the guest and the impurity delayed fluorescence. The decay and the buildup kinetics observed are generally of second order though in the long time region first order kinetics predominates. Both first and second order kinetic analyses have been made. From various Arrhenius plots it has been estabilished that the thermal excitation energy is the T1H–T1D energy gap, suggesting T1D→T1D*→T1H→T1G (or T1(imp)) as the thermally activated process in the guest or the impurity delayed fluoresence generation. Some kinetic parameters have been evaluated and the values obtained suggest that at short times about 80% of the guest or impurity triplets undergo heterofusion and this reduces to about 10% in the long time region.
Piezomodulation spectroscopy of molecular crystals. III. The first singlet system of anthracene
Authors: Merski J. , Eckhardt C. J.
Published: February 2003

The polarized piezoreflection spectra of the first singlet system of anthracene and their Kramers-Kronig transforms are reported. Exciton energy strain shifts are reported for the b-polarized and for the ac-polarized factor group components. These values are shown to be in good agreement with related experimental data and with theoretical calculations. The piezomodulation spectra significantly enhance structure and are also sensitive to the extent of crystal coupling. Deviations in the measured spectra are observed in the a-polarized spectra from that calculated for the logarithmic derivative. These variances are attributed to coupling with the second singlet of anthracene or the presence of the 1Lb transition.
Photofragmentation of CH3I: Vibrational distribution of the CH3 fragment
Authors: Sparks R. K. , Shobatake K. , Carlson L. R. , Lee Y. T.
Published: February 2003

The photodissociation of CH3I at 266 nm is investigated by means of high resolution photofragment spectroscopy. The resolution is sufficient to determine the vibrational population of the CH3 umbrella motion for the I*(2P1/2)+CH3 product channel. An approximate vibrational distribution for the I(2P3/2)+CH3 product channel is also determined. The rotational energy distribution for the CH3+I*(2P1/2) channel is estimated to be on the order of or less than 600 cm−1 wide for each of the CH3 vibrational states. A refined value for the C–I bond dissociation energy of 53.3±0.7 kcal/mole is determined from the energy threshold for the I*+CH3 channel. The vibrational energy distribution for the I*+CH3 channel is discussed in relation to a recent model calculation by Shapiro and Bersohn and possible explanations for the discrepency between the calculated and the measured distributions are considered.
Vibrational relaxation of HF(v = 3, 4, 5) between 300 and 700 K
Authors: Foster T. J. , Crim F. F.
Published: February 2003

Laser excited vibrational overtone fluorescence measurements show an inverse temperature dependence for HF(v = 3, 4, 5) self-relaxation between 300 and 700 700 K. This temperature dependence reflects the dominance of long range forces in the energy transfer dynamics, and the data follow empirical correlations based on formation of transient complexes. Scaling of the relaxation rate with vibrational quantum number is a simple power law vn, with n being insensitive to temperature.
An a
b i
n
i
t
i
o molecular orbital study of NaCN and KCN
Authors: Klein Michael L. , Goddard John D. , Bounds David G.
Published: February 2003

A b initio self-consistent-field calculations using large flexible Gaussian basis sets are reported for sodium and potassium cyanide. The potential energy curves calculated for the linear cyanide, linear isocyanide, and a T-shaped geometry in which Na+ or K+ approaches the center of mass of a rigid (CN)− indicate that the T- shaped minimum is lowest in energy and the linear cyanide structure highest. The fully optimized equilibrium (re) geometries determined for both complexes are significantly nonlinear. Nearly L-shaped structures KNC and NaNC lie ∼1.7 and ∼0.8 kcal/mol lower than the optimized linear isocyanide geometries. For KCN, the optimum geometry is calculated to be re(KC) = 2.850 Å, re(KN) = 2.616 Å, re(CN) = 1.153 Å, ϑe(KCN) = 66.6°, and ϑe(KNC) = 90.5° in good agreement with recent experimental determinations of the gas phase structure. The predicted geometry for NaCN is re(NaC) = 2.470 Å, re(NaN) = 2.195 Å, re(CN) = 1.152 Å, ϑe(NaCN) = 62.7°, and ϑe(NaNC) = 89.5°. The electronic distributions in the complexes are discussed in terms of Mulliken net charges and one-electron properties. The effects of including electron correlation have been estimated on the basis of the London dispersion energy formula which is valid at long range. It is probable that electron correlation corrections will not change the qualitative conclusion of this work that both KCN and NaCN are very floppy molecules which, however, do exhibit nonlinear equilibrium geometries.
Linear vibronic coupling in a general two level system
Authors: Friesner Richard A. , Silbey Robert
Published: February 2003

The energy levels and wave functions for the excited vibronic states of a dimer made up of inequivalent molecules which interact (linearly) with vibrations and are coupled together electronically are treated. Two approximate schemes whose ranges of validity are substantially different and whose results are shown to agree well with exact numerical calculations are given. A discussion of the effect of the vibronic coupling on localization of the wave functions is given.
Higher-order electron correlation effects in triatomic potential energy surfaces. Stretching vibrations of HCN and HNC
Authors: Dykstra Clifford E. , Secrest Don
Published: February 2003

An assessment of the importance of higher-order electron correlation effects on harmonic vibrational frequencies, anharmonicities, and equilibrium structures is made for the simple triatomics HCN and HNC. Potential energy surfaces for bond stretching were generated with a large, polarized basis set of contracted Gaussian functions and using self-consistent field (SCF), correlated self-consistent electron pair (SCEP), and approximate double substitution coupled cluster (ACCD) wave functions. SCEP includes correlating configurations that mix directly with the reference wave function, while ACCD includes these configurations and also indirectly mixing configurations that arise from a cluster model of the wave function. The surfaces are compared in the prediction of spectroscopic parameters by using a low-order perturbational treatment of the vibrational wave functions in a basis of normal mode functions and with several polynomial surface fits. The neglect of correlation effects at the SCF level leads to overestimates of the vibrational frequencies. Higher-order correlation effects correct for roughly one third of this overestimation. For all parameters, the ACCD treatment yields the best predictions.
The limited influence of the Debye–Waller factor on the intensities of high frequency molecular modes measured by neutron inelastic spectroscopy
Authors: Jobic H. , Ghosh R. E. , Renouprez A.
Published: February 2003

Comparison of conventionally calculated vibrational spectra of a molecular crystal with neutron inelastic scattering spectra shows blatant differences which we relate to the very wide range of time scales now measurable. We have measured the complete vibrational spectrum of hexamethylenetetramine between 350 and 3600 cm−1 on beryllium filter spectrometers at several temperatures: 5, 80, and 300 K. We compare the experimental data with computed spectra derived from previously published normal coordinate analyses. At low temperature, we find a good agreement between the observed spectrum and the calculated one-phonon spectrum computed by Thomas and Ghosh. Combination peaks arising from the more intense bands are clearly identified. Numerical calculations of the Debye–Waller factor summed over all frequencies indicate that its value is so small at high energy transfers as to preclude any measurements of high frequency vibrations. However, we show that actual measurements of even C–H stretching frequencies are possible because the mean displacement of the intermolecular modes is zero on this time scale. For HMT (and most molecular crystals) at low temperature the influence of the Debye–Waller factor can be neglected in the comparison of the incoherent NIS spectrum with calculated one-phonon spectra.
Variational method for classical polarizabilities
Authors: Fixman M.
Published: February 2003

We consider a problem equivalent to the inference of the dipole moment induced in an object by a constant applied field. The object has an arbitrarily distributed dielectric tensor and is immersed in the vacuum. A variational expression for the polarizabilities is developed; it provides lower bounds in examples of greatest interest. Matrix representations of the equations are developed for uniaxial symmetry, and tested for the special example of uniform, finite cylinders with arbitrary scalar dielectric constant. In the limit of infinite dielectric constant, very good agreement is found with previous numerical work on conducting cylinders.
Equation of state of site-interaction fluids from the site–site correlation function
Authors: Nezbeda Ivo , Smith William R.
Published: February 2003

It is shown that, using a suitable molecular coordinate system, the equation of state of site-interaction molecular fluids may be conviently calculated, both in the context of computer simulations and of theories. Using a zeroth-order form of perturbation theory, knowledge of only the usual site–site pair correlation function is required to compute the resulting equation of state. The theory is illustrated for all short-range site-interaction fluid models for which computer simulation results are available. For all the models considered, our calculations are very accurate.
EXAFS study of hydrated manganese-exchanged A and Y zeolites
Authors: Morrison Timothy I. , Iton L. E. , Shenoy G. K. , Stucky Galen D. , Suib Steven L.
Published: February 2003

Analyses of the EXAFS of exchanged divalent manganese cations in small pore (A) and large pore (Y) zeolites reveal that the local environments of the cations in the zeolite are similar to the environments of Mn2+ in solution. Further, the EXAFS show no long-range order about the exchanged cations in the zeolite. The implications of the similarity of complexes in the zeolites and in aqueous solution and the lack of long-range order about the intrazeolite cations are discussed.
Thermodynamics of solutions of hydrogen in palladium–manganese alloys. I. Pd3Mn from 555 to 909 K
Authors: Phutela R. C. , Kleppa O. J.
Published: February 2003

The thermodynamic properties of dilute solutions of hydrogen and deuterium in Pd3Mn have been determined by a calorimetric-equilibrium method between 555 and 909 K. This alloy undergoes an order–disorder transition at 750–800 K, i.e., in the temperature range of our measurements. In this temperature region the thermodynamic properties of hydrogen change very significantly. The partial entropies of hydrogen in the alloy are quite low compared to the values in pure palladium; this points toward a highly nonrandom distribution of the hydrogen atoms among the available interstitial sites. From the isotope effect the vibrational frequencies of hydrogen are calculated to be 600 cm−1 at 555 K, 650 cm−1 at 700 K, 770 cm−1 at 777 K, and 860 cm−1 at 807 K, i.e, increasing significantly with increasing temperature. Note in particular the increase in frequency in the transition region. This change correlates with a reduction in the partial entropy of hydrogen of about 1.8 cal K−1 mol−1 from the ordered to the disordered alloy.
An alternative approach to the osmotic coefficient of polyelectrolyte solutions
Authors: Vlachy V. , Bratko D.
Published: February 2003

A new expression for the osmotic coefficient of polyelectrolyte solutions has been derived by differentiating the electrostatic energy with respect to volume at constant electrostatic configurational entropy. The derivation is based on the cell model of polyelectrolyte solutions. The resulting equation relates the osmotic coefficient to the concentration of simple ions adjacent to polyion. The implications of this expression for salt-free solutions and for ternary mixtures are discussed.
Energy accommodation coefficients of internally excited molecules
Authors: Anderson D. R. , Lee E.-H. , Pildes R. H. , Bernasek S. L.
Published: February 2003

A method for determining partial energy accommodation coefficients is described. Laser radiation is used to excite absorbing molecules in the gas phase, which subsequently strike a solid surface depositing energy. This energy transfer is monitored by observing the temperature rise of the solid. Measurement of this temperature rise as a function of gas pressure is used to determine the vibrational energy accommodation coefficient. This method is applied to the interaction of CH3F, SF6, methanol, and cyclopropane with a seasoned molybdenum surface. Values of the vibrational energy accommodation coefficient are found to correlate well with the heat of vaporization of the absorbing molecule.
Photoconductivity studies in some nonpolar liquids
Authors: Casanovas J. , Grob R. , Delacroix D. , Guelfucci J. P. , Blanc D.
Published: February 2003

Measurements of the photoconductivity of liquid n-pentane, n-hexane, cyclopentane, cyclohexane, neopentane, neohexane, and tetramethylsilane induced by far UV radiation (7⩽hν⩽10 eV) have been performed. We have studied the influence of the incident photon energy, of the applied electric field strength, and of the concentration of two electron scavengers (carbon tetrachloride and perfluoromethylcyclohexane). Our results show that in going from the gas phase to the liquid phase, the ionization energy threshold values of these low dielectric constant liquids are lowered by about 1.6 eV. The introduction of an electron scavenger reduces drastically the solvent photocurrent. Our results are consistent with the quenching, by the scavenger, of a solvent expanded excited state, precursor of the geminate ion pair, and not with an epithermal electron scavenging as in high energy photon irradiation.
Monte Carlo simulation of a lattice model of intramolecular exciplex formation
Authors: Fraser Simon J. , Winnik Mitchell A.
Published: February 2003

Monte Carlo simulation on a diamond lattice is used to estimate the intramolecular cyclization probability of a bulky chromophore (benzophenone) joined to an amine quencher by a polymethylene chain. This probability determines the chain length dependence of relative rate constants in exciplex formation between photoexcited amine and chromophore when the intrinsic rate for this reaction is very low and therefore this cyclization is configurationally controlled. The chromophore is represented by suitable, fixed lattice sites in our model, the hydrocarbon chain by a (random) next-neighbor-avoiding walk, and the amine by an orientable group attached to the end of the polymethylene chain. Excluded volume and steric effects are incorporated by singly occupying lattice sites in the chain-growing algorithm (equivalent to hard sphere interactions between the atoms comprising the system). The temperature dependence of cyclization is investigated by giving the chain segments conformational energy. The cyclization probability Pt for this model is calculated as the ratio of the partition function for cyclized configurations to the total (canonical) partition function. For the said cyclized configurations the amine must lie in a suitable orientation within the ’’reactive volume’’ of the chromophore, this volume being represented by appropriate lattice ’’hit’’ sites. Improvements in the chain-growing algorithm permit precise numerical estimates of the chain length dependence of the cyclization probability [at infinite and room temperature (298 °K)]. We have also examined the effect of such parameters as the bulk of the amine quencher, the size and disposition of the reactive volume about the chromophore, and the mean distance of this volume from the chain origin.
Nonexponential decay of fluorescence of jet-cooled isoquinoline related to intermediate level structure of S2–S1 coupling
Authors: Jameson A. Keith , Okajima S. , Saigusa H. , Lim E. C.
Published: February 2003

We report ’’fast’’ and ’’slow’’ components of fluorescence in jet-cooled isoquinoline, which represents the first known observation of biexponential fluorescence that can be attributed to the intermediate level structure of S2–S1 coupling. The slowly decaying component of the emission appears only upon strong internal cooling of the molecule, while the rapidly decaying component appears under all nozzle conditions. The sensitivity of the slow component fluorescence to the internal cooling provides an important clue to the origin of the thermal quenching of fluorescence and triplet formation, which represents one of the most conspicuous photophysical characteristics of molecules with close-lying, lowest energy, nπ* and ππ* singlet states.
Polarization of the 1B2u←1A1g two-photon spectrum of m-C6H4D2: Mechanism of isotopically induced harmonic mode scrambling
Authors: Rava Richard P. , Goodman Lionel
Published: February 2003

Experimental evidence is presented for mode scrambling in the ν18 transition. (AIP)
On representation of Coulomb integral by one-electron functionals
Authors: Gadre Shridhar R. , Pathak Rajeev K.
Published: February 2003

Ground state properties of two-electron atoms and molecules are examined. Wave functions for the ground state of He and singly ionized Lithium are given. (AIP)
A laser flash photolysis kinetics study of the reaction OH+H2O2→HO2+H2O
Authors: Wine P. H. , Semmes D. H. , Ravishankara A. R.
Published: February 2003

Absolute rate constants for the reaction OH+H2O2→k1HO2+H2O are reported as a function of temperature over the range 273<T<410 K. OH radicals were produced by 266 nm laser photolysis of H2O2 and detected by resonance fluorescence. H2O2 concentrations were determined in situ in the slow flow system by UV photometry. An unweighted linear least squares analysis of the ln k1 vs T−1 data gives the Arrhenius expression k1 = (3.7±0.6)×10−12exp[−(260±50)/T] cm3 molecule−1 s−1, where the errors are 2σ and refer to precision only. The estimated accuracy of each k1(T) is ±20%. Our results confirm the findings of two recent discharge flow–resonance fluorescence studies that the title reacton is considerably faster, particularly at temperatures below 300 K, than all earlier studies had indicated.
Vibrational and total energy dependence of the reaction rate of Na with CO2 laser-excited SF6
Authors: Eyal Mark , Grabiner Frederick R. , Agam Uri , Gamss Leonard A.
Published: February 2003

The rate of reaction between sodium and sulfur hexafluoride has been studied as a function of the vibrational energy and total thermal energy of the SF6 in the temperature range 380–440 °K. Vibrational energy was increased by absorption of radiation from a pulsed CO2 laser, and total energy was increased by heating the reaction system. The reaction rate was determined as a function of energy in the time period after the laser pulse when the vibrational energy was equilibrated within the vibrational modes but there was no appreciable relaxation to translational energy. It has been determined that the reaction rate increases with the addition of vibrational energy but is essentially unaffected by additional translational energy. The results are in accordance with a statistical reaction rate theory which suggests that additional translational energy has no further effect in promoting a very exothermic polyatomic reaction.
The kinetics of conformational transitions: Effect of variation of bond angle bending and bond stretching force constants
Authors: Helfand Eugene , Wasserman Z. R. , Weber Thomas A. , Skolnick Jeffrey , Runnels John H.
Published: February 2003

Conformational transitions in chain molecules have been shown to proceed via a reaction coordinate which is a localized mode involving rotations about bonds, and also bond angle bending and bond stretching. By investigating the kinetics as a function of the force constants (flexibility) for bond angle bending and bond stretching, the role of the localized mode is probed. The study reported here consists of computer simulations of the Brownian dynamics of chain motions, and of kinetic calculations of rates and reaction modes. The theory accurately predicts the relative effects of force constant variations on transition rates determined by simulation.
Cross sections for symmetric charge transfer and proton transfer reactions of internal energy selected NH3+ (v)
Authors: Baer Tomas , Murray P. Terrence
Published: February 2003

Absolute total cross sections for electron and proton transfer reactions of NH3 selected in vibrational levels from v = 0 to 10 have been measured by photoion–photoelectron coincidence. The proton transfer reactions were determined at relative translational energies between 0.1 and 1 eV, while the electron transfer reactions were measured between 1 and 100 eV and at 3000 eV. Although the Franck–Condon factors between v = 0 and v = 5 of the NH3 (v = 0)→NH3+ (v) transition change by a factor of 35, the cross sections for charge transfer vary only by a factor of two. By comparing the measured cross sections with the Langevin collision cross sections, we show that the internal energy plays a role only for impact parameters larger than the Langevin orbiting impact parameter. A model which divides the charge transfer reaction into two types, one involving intimate collisions, the other large impact parameter collisions, is introduced. The model is used to derive the charge transfer probability as a function of impact parameter for various combinations of NH3+ vibrational and relative kinetic energies.
Seniority groups for linear polyenes
Authors: Herrick David R. , Liao Chung-Lin
Published: February 2003

The approximate pseudorotation symmetry of linear polyenes CnHn+2 [D.R. Herrick, J. Chem. Phys. 74, 1239 (1981)] is investigated using seniority labels from irreducible representations of subgroup chains of the unitary group U2n. Seniority labels from the spin-dependent symplectic group Sp2n(n = odd) and the rotation group R2n(n = even) are found to quantize completely the alternacy particle–hole symmetry of neutral radicals and molecules in a Pariser–Parr–Pople (PPP) model of valence states. Tables of molecular seniority labels are constructed by a new approach based upon a reduction of the difference character of R2n according to R2n→spin×Spn. Lie algebra generators for subgroups Rn(n = odd) or Spn(n = even) of the spin-free group Un are linked to bond orders between different atoms in the polyene. Details are presented for a new multipole tensor expansion of the PPP Hamiltonian, and certain terms which otherwise break the pseudorotational symmetry are found to vanish identically in the special case of all-trans linear polyenes. Numerical results are presented for the remaining tensor expansion coefficients of several model interactions and suggest a further, approximate simplification of the electron correlation, due to a fortuitous cancellation of terms originating in the long-range and short-range parts of the Coulomb repulsion integral.
Relativistic contributions to the low-lying excitation energies and ionization potentials of the transition metals
Authors: Martin Richard L. , Hay P. Jeffrey
Published: February 2003

Numerical Hartree–Fock calculations have been performed for the lowest terms of the dns2, dn+1s, and dn+2 configurations of the neutral transition metal atoms and the dns and dn+1 configurations of the ions. The excitation energies and ionization potentials are compared with their relativistic counterparts calculated according to the approximate scheme of Cowan and Griffin. The relativistic corrections are large, surprisingly so even for the first transition series, and act to stabilize ’’s-electron rich’’ configurations. They are thus of opposite sign to the electron correlation contributions, which generally tend to stabilize ’’d-electron rich’’ configurations. These correlation effects are particularly severe towards the end of the first transition series. Estimates for relativistic corrections from perturbation theory agree well with relativistic SCF calculations for the first and second transition series but depart substantially for the third series. The excitation and ionization energies from the relativistic calculations are compared with the experimental values (averaged over J states) to observe the overall trends in the correlation contributions.
Homodyne light beating spectroscopy of o-terphenyl in the supercooled liquid state
Authors: Fytas G. , Wang C. H. , Lilge D. , Dorfmüller Th.
Published: February 2003

The laser light scattering intensity fluctuations of supercooled liquid o-terphenyl at temperatures between 12 and −15 °C have been studied using the photon-correlation technique. The time correlation functions obtained using the VV and VH scattering configurations at 90° scattering angle show a wide distribution of relaxation times. Angular-dependent measurements at 45°, 90° and 135° scattering angles show that the time correlation functions for VH and for VV are independent of scattering angles. The VV and VH correlation functions cannot be fit to a bimodal distribution function; neither can they be fit to a cumulant expansion expression with less than four cumulants, but they can be satisfactorily fit to the William–Watts distribution function. The mean relaxation times derived for both isotropic and anisotropic scattering processes from the VV and VH correlation functions are nearly equal. The temperature dependence of the relaxation times cannot be described by an Arrhenius equation with a constant activation energy. The average orientational relaxation times change by more than ten orders of magnitude in the temperature range between 147 and −16 °C but the temperature dependence of the orientational relaxation times over this wide dynamic range can be excellently correlated with the modified Debye–Stokes–Einstein equation. The closeness of the mean orientational relaxation time to the mean structural relaxation time is interpreted as due to strong rotation–translation coupling in the viscoelastic state. It is found that within the dynamic range of the autocorrelator, the collective shear wave plays no role in the time dependence of the VV and VH correlation functions. Quentrec’s theory of viscoelasticity based on the coupling of the shear wave to local translational order and orientational order is found to disagree with the experimental result. Comparison with the dielectric relation time data shows that in o-terphenyl the dielectric relaxation and the present light beating techniques probe different types of motions.
Raman scattering and structure of normal and supercooled water
Authors: D’Arrigo G. , Maisano G. , Mallamace F. , Migliardo P. , Wanderlingh F.
Published: February 2003

Raman spectra in the O–H stretching band in normal and supercooled water have been investigated. Spectra are taken as a function of temperature in the range +95 to −24°C. Absolute Raman cross sections corrected for instrumental and physical factors are obtained. It is shown that the isotropic O–H stretching bands in the range +20 to +95 °C are due to the contribution of ’’open’’ (or tetrahedrically bonded) and ’’closed’’ water that are temperature independent. The percentage of open water α(T) is connected and interpreted in the frame of the Stanley site percolation model. As a consequence, the isobestic point is obtained. In the supercooled region, a third spectral contribution arises, which is centered near the main peak of the isotropic O–H band of ice. Such a contribution is tentatively explained as the presence in supercooled water of true ice, as a heterophase fluctuation.
Competition between stimulated emission and absorption losses from the B state in I2 lasers
Authors: Keller Richard A. , Truesdell Keith A.
Published: February 2003

The optical gains observed in molecular iodine lasers are the result of competition between stimulated emission and absorption losses from the excited B electronic state. The ratio of the cross sections for stimulated emission and absorption is ∼2.5 (v″ = odd) and ∼1.0 (v″ = even) for v′ = 43→v″ = 7–15. The correct consideration of this competition removes the apparent anomaly of nonobservable laser emission to v″ = even in this spectral region.
Laser-induced fluorescence of the NaRb molecule
Authors: Takahashi Naohisa , Katô Hajime
Published: February 2003

Several series of laser-induced fluorescence lines of the heteronuclear alkali dimer NaRb have been observed when a mixture of sodium and rubidium is irradiated by the He–Ne, Ar+, or Kr+ laser line. The spectroscopic constants of the X 1Σ+ ground state have been determined and the potential energy curve has been calculated by the RKR method. RKR potential curves for the excited B 1Π and D 1Π have been determined by comparing the observed and calculated intensity distributions as well as the transition energies. The dependence of the transition dipole moment upon the internuclear distance has been estimated. The fluorescence of the D lines of Na and Rb atoms and a less intense fluorescence, which is assigned as a transition to the a 3Σ+ state in NaRb, have been observed. From the measured vibrational spacing, which can be followed close to the dissociation limit, the dissociation energy De of the a 3Σ+ state is determined to be 568±5 cm−1.
Chemiluminescence of ethylene in an inert matrix and the probable infrared spectrum of methylene
Authors: Lee Yuan-Pern , Pimentel George C.
Published: February 2003

Photolysis of diazomethane in solid matrices at 6 or 10 °K and its subsequent thermoluminescence have been reinvestigated. At 11–12 °K, the thermoluminescence consists of a broad emission at 5220±4 Å and a weak progression with spacing 338 cm−1 in the 6000–7600 Å region, the latter probably due to an impurity. Above 15 °K, the spectrum is dominated by a broad emission (180 cm−1 FWHM) centered at 5987 Å, the red glow detected earlier. The emitter responsible for the 5220 Å feature is not clear, though the frequency is close to that of the atomic N(2D→4S) transition. The 5987 Å emission is best assigned to the C2H4(Z or V→T) transition excited through the reaction of CH2(3B1) molecules either with CH2 or CH2NN. This C2H4 transition has not previously been accessible to experiment. The infrared spectra of the photolysis products at 10 °K indicate that absorptions at 1115 cm−1 (Ar) and 1109 cm−1 (Xe) can be attributed to ν2, the bending mode of CH2 in its ground state. This assignment may be of significance in the interpretation of photoelectron detachment measurements of the CH2 triplet–singlet splitting, tending to favor the 9 kcal/mole value.