bluuebunny/crossref_metadata_2025 huggingface dataset:
SCF calculations of the CH-stretching overtone intensities in dichloromethane within the local mode model
Authors: Tarr Allan W. , Swanton David J. , Henry Bryan R.
Published: July 2002

Oscillator strengths for the CH-stretching components of the overtone spectrum of dichloromethane are calculated for ΔvCH ≤4. The calculations use local mode theory to obtain the vibrational wave functions and SCF theory, with a number of different basis sets, to obtain the dipole moment functions. A comparison with experimental results shows the calculations can reproduce the relative ordering of the oscillator strengths as a function of the particular vibrational state, and give a reasonably quantitative account of the magnitude of the intensities, even with simple split-valence basis sets.
Interaction of a polymer chain with an asymmetric liquid–liquid interface
Authors: Wang Zhen-Gang , Nemirovsky A. M. , Freed Karl F.
Published: July 2002

A continuum model is presented for polymer chains near an asymmetric (A–B) liquid–liquid interface where each side of the interface can have different polymer–surface interactions. For example, one side can attract the macromolecule, while the other can repel it. The model contains different monomer free energies and different excluded volume interactions for the macromolecule in the two solvents. The model is solved exactly in the ideal limit where excluded volume vanishes in order to illustrate qualitatively the wide range of possible behavior. We evaluate the fixed end-vector distribution, some moments of this distribution, and discuss other distributions and several interesting limiting cases. This rich model is constructed based on physical considerations and on consistency requirements which are imposed on any zeroth-order model when it is used in conjunction with renormalization group methods to incorporate the excluded volume interactions.
MSXα calculation of the electronic structure of Cu+ and Ag+ ions in lithium chloride single crystal
Authors: Moine B. , Chermette H. , Pedrini C.
Published: July 2002

The multiple-scattering Xα method applied to an embedded (MCl6)5− cluster (M=Ag,Cu) is used to describe the electronic structure of Ag+ and Cu+ in the LiCl crystal. Several calculations have been performed with different impurity–ligand distances in order to reach the equilibrium distance. The vibrational energy of the breathing mode is deduced from the total energy variation of the cluster vs the bond distance. The multiplet level diagrams obtained after a calculation of spin-orbit interactions are shown and compared with the spectroscopic features.
Rydberg states of NO trapped in rare gas matrices
Authors: Chergui M. , Schwentner N. , Böhmer W.
Published: July 2002

Several new progressions consisting of broadbands have been observed in the absorption spectra of NO trapped in rare gas matrices. They are identified as the blue shifted transitions to the n=3 (A 2Σ+,C 2Π,D 2Σ+) and n=4 (E 2Σ+,K 2Π,M 2Σ+) Rydberg states of NO in Ne matrices and to the n=3 Rydberg states in Ar, Kr, and Xe matrices. Linewidths (50 to 180 meV) and matrix shifts (0.3 to 1.2 eV) decrease from neon to xenon matrices. For each matrix, the shifts decrease according to the symmetry of the excited state orbital, in the sequence sσ–pσ–pπ. An attempt to apply the quantum defect formula with values, for the Rydberg constant and the ionization potential of the matrix isolated molecule taken from literature, fails to describe the vertical transition energies of n=3 and n=4 states in neon matrices. On the other hand, using the adiabatic energies of 3sσ and 4sσ states to generate a series shows that the vertical transitions of n≥5 states lie in the ionization continuum. This could explain the nonobservation of n>4 states in Ne matrices. In the heavier matrices, this model predicts n=4 states but their existence is not borne out by experiment. The Wannier model also fails to describe these transitions.
Semiclassical mechanics of dissipative molecular processes: The correspondence principle and population relaxation
Authors: Parson Robert P. , Heller Eric J.
Published: July 2002

The relaxation of a primary system coupled weakly to a bath of environmental modes is examined from the standpoint of recent developments in the semiclassical theory of molecular bound states. Emphasis is placed upon highly excited, strongly nonlinear (but quasiperiodic) primary systems and zero temperature baths. The starting point for the analysis is a master equation for the populations of the eigenstates of the primary system. The correspondence principle provides semiclassical approximations to the transition rates, allowing quantum state populations to be calculated from classical trajectories. A second semiclassical approximation leads to an equation of motion for a probability density in the classical action variables. As h→0, this density agrees with the density generated by running an ensemble of damped classical trajectories and averaging out the angle variables; retention of terms of order h provides smoothed quantum corrections. Numerical examples of both semiclassical approximations are presented.
Infrared spectrum of the overtone band 2ν5 of the hydrogen bonded complex HCN---HF
Authors: Jackson M. W. , Wofford B. A. , Bevan J. W. , Olson W. B. , Lafferty W. J.
Published: July 2002

The infrared spectrum of the overtone of the ‘‘intramolecular’’ bending vibration 2ν05 of the hydrogen bonded complex HCN---HF centered at 1437.539 91(24) cm−1 has been obtained with a resolution of 0.006 cm−1. Line assignments for this band as well as two hot bands 2ν05+ν17−ν17 and 2ν05 +2ν27−2ν27 have been made, and rotational constants for all the levels involved have been determined. Despite the fact that the higher J energy levels of the observed lines of 2ν05 are above the dissociation energy of the complex, no predissociative line broadening is apparent.
Molecular beam studies of open-shell systems: The van der Waals interaction between O(3P) and He(1S)
Authors: Aquilanti V. , Candori R. , Luzzatti E. , Pirani F. , Volpi G. G.
Published: July 2002

The absolute integral cross sections for oxygeg atom collisions with helium atoms have been obtained. From these cross sections, the interaction between He and ground state oxygen was calculated.(AIP)
The vibrational force field of all-t
r
a
n
s polyene chains
Authors: Tasumi M.
Published: July 2002

The vibrational force field recently proposed by Takeuchi et al. for polyene chains is criticized on the basis of the normal coordinate calculations for tetradesmethyl-β-carotene, a polyene molecule with an intermediate length of conjugation.
Measured radiative lifetimes for H2 and HD in the E,F 1Σ+g electronic state
Authors: Chandler David W. , Thorne L. R.
Published: July 2002

We have used tunable, pulsed ultraviolet laser radiation to prepare H2 and HD in selected rovibronic levels of the E,F 1Σ+g electronic state. This state is accessible from the ground state, X 1Σ+g , by means of two-photon excitation. Subsequent absorption of near infrared laser radiation by molecules prepared in the E,F 1Σ+g state produces ions that are detected by a time-of-flight mass spectrometer. Radiative lifetimes of individual rovibronic levels are determined by measuring the ion signal as a function of the time delay between the ultraviolet and near-infrared laser pulses. A decreasing exponential function is fit to the ion signal associated with a particular rovibrational level to obtain its liftime. Measured lifetimes are in good agreement with previously reported theoretical lifetimes and the single previous measurement.
Computer simulation of dipolar fluids. Dependence of the dielectric constant on system size: A comparative study of Ewald sum and reaction field approaches
Authors: Gray C. G. , Sainger Y. S. , Joslin C. G. , Cummings P. T. , Goldman S.
Published: July 2002

We report Monte Carlo calculations on a Stockmayer fluid ( μ*=1, T*=1, ρ*=0.8) using both Ewald sum (EW) and reaction field (RF) approaches. We investigate the dependence of dielectric constant on system size. This dependence is less marked for EW than for RF. However, for a given number of particles the RF run time is substantially shorter. Both methods therefore offer some computational advantage. Overall, RF is to be preferred because of greater ease of programming.
Consistently averaged hydrodynamic interaction for Rouse dumbbells: The rheological equation of state
Authors: Öttinger Hans Christian
Published: July 2002

A connection between the kinetic theory of the hydrodynamic interaction and continuum mechanics is established. Namely, the rheological equation of state for the Rouse dumbbell model with consistently averaged hydrodynamic interaction is derived. Several applications of this equation of state are discussed.
Examination of the effects of van der Waals molecules on the thermal electron attachment to NO2 at relatively high pressures
Authors: Shimamori Hiroshi , Hotta Hiroshi
Published: July 2002

Thermal electron attachment to NO2 in He, Ar, Xe, N2, CO2, and n-C4H10 has been studied at pressures from about 100 Torr to near one atmosphere. With the increase of buffer-gas pressures the effective two-body attachment rate constants tend to increase gradually from the value of 1.1×10−10 cm3 molecule−1 s−1 obtained in the previous study as the initial two-body attachment rate constant (k1) of the two-step three-body process; the only exception is He, for which no such increase of the rate constant has been observed. These results suggest that in all the buffer gases except for He the electron attachment to van der Waals molecule (NO2⋅M), where M is a buffer-gas molecule, appears at higher pressures. But for He as the buffer gas such a mechanism is negligible in the pressure range employed here, because the equilibrium constant for the complex formation is very small in this case. The rate constants for the electron attachment to van der Waals molecules are about two orders of magnitudes larger than the value of k1 and have no appreciable correlation with the nature of buffer gases.
Random sequential adsorption onto the surface of small spheres
Authors: Rosen L. A. , Seaton N. A. , Glandt E. D.
Published: July 2002

The irreversible random sequential adsorption of spherical particles onto the surface of a spherical substrate was investigated by Monte Carlo simulation. The planar angle α subtended by the adsorbate particles on the substrate ranged from 22.5° to the tetrahedral value of 109.47°. Results are reported both at fixed coverage and at fixed time. The average maximum coverage θmax, which peaks at α=90°, is compared to known close-packed densities for the geometries considered. The applicability of Feder’s limiting law, expressing the time dependence of the coverage as proportional to t−1/2, is confirmed for α≤90°. For α≥109.47°, a t−2/3 dependence is found instead.
The microwave spectrum of propyne in the 17 to 72 GHz region for the v9=2 vibrational state
Authors: Rhee W. M. , Roberts J. A.
Published: July 2002

Some rotational components in the v9=2 vibrational state of propyne have been determined in the frequency range 17–72 GHz. Molecular constants for this vibrationally excited state have been determined from more than 11 observed rotational transitions. Experimentally measured frequencies are presented and compared with those calculated using the results of basic perturbation theory. A constant set was obtained for the v9=1 and v9=2 vibrationally excited levels using the experimental data obtained for the ground and these two vibrational levels. Agreement was found to be quite good for all except one component which may be perturbed by combination bands.
Doppler-free saturation spectroscopy of polyatomic molecules: Photochemical hole burning of gas phase s-tetrazine
Authors: Kiermeier A. , Dietrich K. , Riedle E. , Neusser H. J.
Published: July 2002

Doppler-free spectra of two vibronic bands in the Ã (1B3u)←X̃ (1Ag) transition of the photochemically instable s-tetrazine (H2C2N4) are presented. For the first time saturation spectroscopy is successfully applied to a large polyatomic molecule. Photochemical decomposition of s-tetrazine molecules takes place after excitation and prevents the molecule from returning to the ground state by radiation and nonradiative processes. This represents a particular type of hole burning in the ground state velocity distribution. The elimination of the inhomogeneous Doppler broadening enables us to determine collisionless homogeneous linewidths. For the 0–0 band a value of γ=190 MHz is found whereas the 16a11 band at higher excess energy (ν′16a =256 cm−1) shows a sharper linewidth of γ=140 MHz. No rotational dependence of the linewidth is found in the 0–0 band up to J levels higher than 70. It is argued that internal conversion to the X̃ (1Ag) state is the process responsible for the observed linewidths and that dissociation takes place on the electronic ground state potential surface.
The electronic structure of an atom in the vicinity of a solid body: Application to the physisorption on metal surface
Authors: Girard C.
Published: July 2002

A unified treatment of the modification of the electronic charge density for an atom placed in the vicinity of a solid body is presented. The nonlocality effects inside the two partners is introduced through the generalized susceptibility theory. Applications to the physisorption is proposed by treating the solid body as a nonlocal electron gas limited by a planar surface. When the extended system reduces to a single atom one recovers various results previously proposed for couples of centrosymmetric systems.
The X̃-state spectroscopy of molecular ions: Stimulated emission pumping spectra of the diacetylene cation
Authors: Celii Francis G. , Maier John P. , Ochsner Martin
Published: July 2002

The feasibility of utilizing stimulated emission pumping (SEP) spectroscopy in a reaction environment is demonstrated. As a method for performing vibrational spectroscopy, the SEP technique enables location of rovibrational levels in the ground electronic state. Specific SEP transitions of the open-shell diacetylene cation have been measured and levels in the X̃ 2Πg state are identified. Transitions within two spin-orbit manifolds are differentiated and assigned using this double resonance technique.
Overtone vibration initiated unimolecular reaction of tetramethyldioxetane in a free jet expansion: A comparison with RRKM theory
Authors: McGinley E. S. , Crim F. F.
Published: July 2002

Vibrational overtone excitation of tetramethyldioxetane in a free jet expansion creates a nearly monoenergetic ensemble of molecules for which the unimolecular reaction rate is directly measured by monitoring the temporal evolution of the electronically excited acetone formed in the reaction. The measurement for the 5νCH vibrational overtone transition determines the unimolecular reaction rate constant at one energy. It is possible to adjust the parameters in the RRKM calculation of the rate constant to obtain agreement with this nearly monoenergetic measurement and to average the calculated energy dependent rate constant over a thermal distribution of initial vibrational energies for comparison with data on room temperature samples. The calculation reproduces the growth of the chemiluminescence following excitation of two CH stretching transitions 4νCH and 5νCH and of a combination transition involving the methyl deformation 4νCH +νdef.
Constant ionic state spectroscopy of N2O. Dispersed fluorescence as a probe of molecular autoionization
Authors: Poliakoff E. D. , Ho Ming-Hang , Leroi G. E. , White M. G.
Published: July 2002

We report electronic autoionization studies of N2O using vibrationally resolved constant ionic state (CIS) spectroscopy. Vacuum ultraviolet synchrotron radiation is the excitation source, and we determine the relative partial photoionization cross-section curves for alternative vibrational levels (v′) of the ion by detecting dispersed fluorescence [N2O+(A 2Σ+,v′→X2Π,v″)] from the ion. Excitation spectra sampling different vibrational levels reveal significant changes in the 3pπ resonance profile, including shifts of the resonance minima, and previously unobserved features. Analysis of the v′=(0,1,0) CIS spectra demonstrate that this level of the ion is produced predominantly by photoionization of the target molecules in the (0,1,0) level, i.e., via hot band excitation. These results are discussed in detail, as well as possible extensions and further studies.
Chaotic structure in the phase space of acetylene
Authors: Farantos Stavros C.
Published: July 2002

The classical dynamics of acetylene, vibrationally excited, reveals the existence of bottlenecks in the isomerization process of acetylene to vinylidene. It is shown that there is a correlation of the rate of exponential divergence and isomerization. Trapped trajectories have smaller rates of exponential separation than those which lead to isomerization.
High resolution FTIR spectra of CDF3 in the CD stretching fundamental and overtone regions
Authors: Dübal H.-R. , Lewerenz M. , Quack M.
Published: July 2002

FTIR spectra of 12CDF3 are reported at resolutions up to 0.006 cm−1 for the CD stretching fundamental and overtone transitions. For the band associated most closely with the CD stretching fundamental, the rotational J and K structure is largely resolved and analysis gives ν̃eff1=2261.2637 cm−1, A′=B′=0.329 5858 cm−1, C′=0.189 0758 cm−1, D′J=3.006×10−7 cm−1, DJK=−3.62×10−7 cm−1, and D′K=1.94×10−7 cm−1. (For further constants see Tables I and 2). The large value of B″−B′=0.001 347 cm−1 is interpreted in terms of a strong Fermi resonance between ν1 and 2ν2 (symmetrical CF3 stretching vibration) with an effective two-state coupling constant ‖k122‖≂80 cm−1. Alternatives to this assignment are discussed and it is shown that the two-state coupling model is only part of a larger coupling scheme involving several states in addition to 2ν2. The rotational structure of the second Fermi resonance component shows severe perturbations for values of K>33. Analysis of 157 assigned lines gives a band center at 2152.2796 cm−1, with unusual ΔB and ΔC values providing further evidence for multistate interactions. This interpretation is also supported by the structure of the CD overtone transition (2νeff1=4383.858 cm−1) and further evidence. The results are discussed in relation to Fermi resonances observed in CHF3 and substantial differences in vibrational redistribution involving the CH and the CD chromophores are observed.
Correlation functions for restricted rotational diffusion of articulated bodies
Authors: Kumar Anil , Levy George C.
Published: July 2002

The correlation functions are derived for the reorientational dynamics in solution of flexible molecules based on the flexible molecule modeled as an articulated body with rigid subunits. A generalized rotational diffusion equation is obtained. Specific models include: (i) rotational diffusion of an arbitrary shaped body with internal motion-in-a-cone with additional jump motion and (ii) arbitrary shaped body with two or more internal motions in cones. The theory is applicable to reorientational dynamics of macromolecules in dilute solution.
An analysis of the electron density distribution in the free and polarized H2O molecule as calculated in the local density approximation
Authors: Krijn M. P. C. M. , Feil D.
Published: July 2002

The Xα version of the LD approximation has been applied to H2O, resulting in a dipole moment and dipole polarizability of CI quality when augmenting the basis set with d- and f-type polarization functions. The behavior of the electron density upon placing the molecule in a small external homogeneous electric field has been investigated and depicted in the form of difference density maps.
Electron thermalization processes in a He–Kr bicomponent system and a Ne pure system
Authors: Suzuki Etsuhito , Hatano Yoshihiko
Published: July 2002

Time evolutions of electron mean energy in a He–Kr bicomponent system and a Ne pure system are observed by means of a pulse-radiolysis microwave-conductivity method, assuming that an electron energy distribution function is always Maxwellian in the energy range from about 100 meV to thermal. Excess electron temperature Te–Tg decays exponentially, whose decay time is defined as a thermalization time. Products of gas pressure and thermalization time are estimated to be 9.7 Torr μs for He, 1.0×103 Torr μs for Ne, and 1.7×102 Torr μs for Kr. The present result for Kr obtained from the He–Kr bicomponent system is in good agreement with that obtained from the Kr pure system.
Susceptibility and Mössbauer study of coupled admixed-spin state in [Fe(OEP) (3-ClPy)]+ dimers
Authors: Gupta G. P. , Lang George , Scheidt W. Robert , Geiger David K. , Reed Christopher A.
Published: July 2002

Susceptibility measurements of [Fe(OEP) (3-ClPy)] ⋅ ClO4(OEP=octaethylporphyrinate) in an external field of 1 T show that its magnetic moment varies from 3.36 to 4.58 β over a temperature range of 6–300 K. The data were analyzed with the ‘‘Maltempo model’’ but could be fitted only when an antiferromagnetic exchange interaction between two neighboring iron atoms within the dimer structure was assumed. The analysis shows that the ground state quartet S=3/2 (81%) is mixed with the nearby sextet S=5/2 (19%) through spin-orbit coupling with an unusually small coupling constant, ζ=150 cm−1. The exchange interaction within the dimer is estimated to be in the range of J=−0.4 to −0.6 cm−1. Mössbauer spectra of a polycrystalline sample of this complex were recorded in a range of temperatures (1.54–128 K) and applied magnetic fields (0–6 T). The analysis of Mössbauer spectra was in excellent agreement with that of susceptibility data. The analysis favors J=−0.6 cm−1. The values of chemical shift, δ=0.36 mm/s (with respect to metallic Fe), and temperature independent quadrupole splitting ΔE=3.23 mm/s, are typical of ferric ions in the admixed-intermediate spin state. Mössbauer analysis also provides the hyperfine coupling constant, P/gNβN =36.3 T/unit spin, a very low value compared with 60 T/unit spin for hemoglobin fluoride. The spectra also show that the system relaxes slowly in the presence of an external field above 5 T at 4.2 K. The rate of relaxation increases if the field is decreased or the temperature is increased. Low temperature spectra with intermediate rates of relaxation could be fitted with the set of parameters mentioned above. Only the direct relaxation process seems to be responsible up to 8 K. The anomalously large value of ΔE and low values of ζ and P are discussed in terms of the formation of molecular orbitals and changing radial wave functions of the 3d orbitals in the admixed-spin states.
Rotational state distribution of CO photofragments from triplet ketene
Authors: Bitto Herbert , Chen I-Chia , Moore C. Bradley
Published: July 2002

The nascent rotational state distribution of CO(v″=0,J″) following excimer laser photolysis of ketene at 351 nm has been determined under collisionless conditions in a flow cell. At this low excitation energy dissociation can only take place on the triplet potential surface leading to CH2(X̃ 3B1) and CO(X̃ 1Σ+). The available energy permits only the vibrational ground state of CO to be populated. The observed rotational distribution of CO(v″=0,J″) deviates drastically from a phase space theory statistical distribution as well as from a thermal one. A Boltzmann plot of this distribution exhibits a population inversion for J″<13. The nonstatistical behavior is attributed to a barrier along the dissociation path. The fragments are repelled too rapidly for energy to be randomized between them. Thus the photofragmentation dynamics of triplet ketene contrasts markedly with dissociation on the singlet surface which has no barrier and gives a statistical CO rotational state distribution. An impulsive model calculation for the ab initio transition state geometry is in surprisingly good agreement with the experimental energy partitioning among the fragment degrees of freedom. This suggests that the CCO bond angle is strongly bent at the top of the barrier and that the barrier height is a substantial fraction of available energy.
Anharmonic asymmetric oscillator: A classical and quantum treatment
Authors: Bejarano J. Díaz , Sánchez A. Martin , Rodríguez C. Miró
Published: July 2002

The nonrelativistic anharmonic–asymmetrical–oscillator (AAO) is studied in full. The classical equation of motion is solved using Jacobi elliptic functions which have both real and imaginary periods. The imaginary period is connected with the imaginary part of the energy in quantum mechanics. The resonances (Siegert states) are calculated in the JWKB approximation.
Decoupling of the local mode stretching vibrations of water through rotational excitation. I. Quantum mechanics
Authors: Shirts Randall B.
Published: July 2002

We demonstrate that in a previously studied model of the stretching modes of the water molecule rotational motion in the plane of the molecule tends to decouple the stretches. For rotational angular momentum near  J=18 ℏ, the two local mode stretches are almost entirely decoupled. The source of this decoupling is the centrifugal distortion which stabilizes the asymmetric stretch and effectively cancels the G-matrix coupling. This cancellation is clarified using three different methods: Direct examination of the numerically computed matrix elements, exact analytic matrix elements of an approximate Hamiltonian, and solutions of a Mathieu equation formulation of a classical resonance Hamiltonian. The importance of this result is discussed in light of the fact that strong rotational excitation can occur in infrared multiple photon excitation. If such rotational decoupling occurs in real systems, then intramolecular energy transfer would be diminished thus holding open the possibility of mode specific infrared excitation. The calculations were carried out by numerically evaluating matrix elements between a basis of Morse oscillator eigenstates using an efficient Gaussian quadrature scheme based on associated Laguerre polynomials.
Influence of pure reorientational processes on magneto-chiral birefringence and dichroism of diamagnetic molecules in strong optical fields
Authors: Woźniak S.
Published: July 2002

The theory of magneto-chiral birefringence and dichroism is extended to systems composed of diamagnetic molecules acted on by an optical field. For molecules with the point group symmetries 3, 4, 6, ∞, 32, 422, and 622 expressions are derived for the magneto-chiral birefringence and dichroism in the presence of weak as well as very strong optical molecular reorientation caused by a linearly polarized, circularly polarized, or unpolarized laser beam. Measurements of magneto-chiral birefringence and dichroism at optical saturation provide direct information on the respective magnetic dipole and electric quadrupole polarizability tensor components.
Spectroscopy of N+2 Meinel bands and CO+ comet tail bands
Authors: Kuo C.-H. , Milkman I. W. , Steimle T. C. , Moseley J. T.
Published: July 2002

The N+2[X2 Σ+g(v″=0)– A 2Πu(v′=5)] Meinel band and the CO+[X 2Σ+(v″=0)– A 2Π(v′=1,2)] comet tail bands have been measured with Doppler-limited resolution in a selected ion flow tube (SIFT) apparatus using laser induced charge transfer. The charge transfer medium was Ar, which does not react with those ions in their ground levels, but undergoes a strong charge transfer reaction with the excited states under consideration here. The use of a single mode laser and the SIFT technique led to much higher signal-to-noise than obtained in earlier work. These measurements are the first reported with Doppler-limited resolution on any of these bands, and are analyzed to provide substantially improved molecular constants for the excited states involved in the transitions.
Relativistic calculations of electronic states and potential energy surfaces of Sn3
Authors: Balasubramanian K.
Published: July 2002

Complete active space MCSCF (CASSCF) followed by multireference singles and doubles CI (MRSDCI) calculations are carried out on the low-lying electronic states of Sn3. Relativistic effective core potentials with the outer d10s2p2 shell as the valence shell are employed for the tin atom. Calculations of a number of electronic states of both equilateral and isoceles triangular structures reveal the existence of two nearly degenerate structures. The ground state of Sn3 is found to be the 1A1 state (isosceles triangle) with re=2.723 Å and an apex angle of 83°. The 3A′2 state arising from the equilateral triangular structure is about 4 kcal/mol above the 1A1 state in the absence of spin-orbit interaction. The properties of the low-lying electronic states of Sn3 are compared with Si3. The bending potential energy surfaces of the 1A1 and 3B2 states are calculated. It is predicted that the potential energy surface of the ground state of Sn3 (A1) in the presence of spin-orbit interaction would contain a double minima separated by a small barrier. Thus it is predicted that the Sn3 cluster would be floppy at room temperature. The atomization energy of the ground state is estimated to be about 71 kcal/mol without spin-orbit interaction and 48 kcal/mol in the presence of spin-orbit interaction. The Sn3 cluster is found to be slightly more stable than Sn2.
On the possibility of nonadiabatic transitions in the photodissociation of I2M clusters excited above the dissociation limit of the B state
Authors: Beswick J. Alberto , Monot R. , Philippoz J.-M. , van den Bergh H.
Published: July 2002

The reaction I2M→hν I2(B,v′, j′)+M has been studied experimentally for excitation above the dissociation limit of the I2M B state. A surprisingly large amount of the available energy is found as relative translational energy of the I2 and M products. These results have been interpreted in terms of a one atom ‘‘cage effect,’’ where the iodine atoms are prevented from dissociating by the presence of the rare gas atom M. A purely kinematic cage effect could occur on a single electronically excited potential energy surface, namely the one correlating to the I2(B) state plus M in its electronic ground state. In this paper we discuss another possible mechanism for a pathway leading to bound I2, which involves an electronic nonadiabatic transition. Above the I2M(B) threshold the 1Π1u electronic state can also be excited. Since the 1Π1u and the B states can be coupled by the presence of the rare gas atom, there is a finite probability for an electronic transition from 1Π1u to B, with the energy difference being transformed into relative kinetic energy of the rare gas atom with respect to I2 after a fraction of the available energy has been used to break the van der Waals bond. The relationship between this mechanism and the electronic predissociation of I2M(B) van der Waals molecules at much lower energies, as well as the collision induced electronic predissociation of I2(B), are also mentioned. Finally the possibility of observing similar transitions in other halogen–rare gas clusters is considered.
Infrared laser kinetic spectroscopy of a photofragment CS generated by photodissociation of CS2 at 193 nm: Nascent vibrational–rotational–translational distribution of CS
Authors: Kanamori Hideto , Hirota Eizi
Published: July 2002

Carbon monosulfide fragments generated by CS2 photodecomposition at 193 nm were examined by time-resolved observation of their vibration–rotation spectral lines with infrared diode laser kinetic spectroscopy. The CS molecules were found to be initially spread over a wide range of vibrational and rotational levels which were accessible with available energy, for both the triplet and singlet channels leading to sulfur atoms in the 3P ground and 1D excited states, respectively. The analysis of the observed line shape has allowed us to obtain information also on translational energy of CS fragments and to distinguish the contributions of the two channels. The branching ratio was thus estimated to be approximately one to one.
Solution of the generalized Langevin equation for a polymer in a solvent
Authors: Toxvaerd So/ren
Published: July 2002

The solvent effect on the structure and dynamics of a polymer is determined by solving the generalized Langevin equation (GLE) for a nonamer in a solvent. The solution is compared with the corresponding molecular dynamics (MD) result and with the behavior of a free polymer. Good agreement is obtained between GLE and MD. The GLE calculation, however, are decades faster than the MD and so the system easily can be followed over 10−8 s, which is found to be necessary in order to determine the mean shape of the nonamer.
Chemical sputtering of nickel oxide and carbide by low energy (5–200 eV) C+ and O+ beams
Authors: Kang Heon , Kasi Srinandan , Rabalais J. Wayne
Published: July 2002

Recombination of carbon and oxygen on a Ni(111) surface has been studied by low energy (5–200 eV) reactive ion bombardment (RIB). The reactions O++NiC(s) and C++NiO(s) both result in efficient removal of the surface carbon and oxygen, respectively. Removal of the adspecies occurs most efficiently at low kinetic energies and the rate of sputtering decreases with increasing kinetic energy. Energy dissipation into the solid appears to be insufficient for stabilization of the molecular CO product as a surface adsorbate.
Time-resolved spectroscopic measurements on microscopic solvation dynamics
Authors: Nagarajan V. , Brearley Ann M. , Kang Tai-Jong , Barbara Paul F.
Published: July 2002

This paper reinvestigates the use of transient fluorescence spectroscopy of polar aromatics in solution as a method to determine microscopic solvation dynamics. It is shown that the compounds previously employed as polar fluorescent probes tend to fall into three photophysical classes depending upon: (i) whether the photon induced change in μ occurs simultaneously with photon absorption (ii) whether solvent motion subsequent to photon absorption is required to induce the change in μ; or (iii) whether two excited-state isomers with different μ’s are present simultaneously. The consequence of the different classes on microscopic solvation dynamic measurements is discussed with a molecular example for each class: (i) 4-aminophthalimide, (ii) 4-(9-anthryl)-N, N-dimethylaniline, and (iii) bianthryl, respectively. In addition, we introduce a new transient fluorescence procedure for the determination of solvation dynamics that has advantages over the traditional transient Stokes-shift method. Finally, for the first time, extensive measurements on the solvation dynamics of a polar aprotic solvent have been made. The observed dynamics of the solvent (glycerol triacetate) are highly nonexponential; this has important implications for chemical reactions in similar solvents. Interestingly, the experimentally observed microscopic dynamics are in qualitative agreement with predictions of the dielectric continuum model.
Fluorescence polarization studies of autoionization in CS2
Authors: Poliakoff E. D. , Dehmer J. L. , Parr A. C. , Leroi G. E.
Published: July 2002

The polarization of the CS+2(A 2Π→X 2Π) transition was measured following photoionization of CS2 with synchrotron radiation excitation in the range 875 Å<λexc <967 Å. Autoionization features are prominent in the fluorescence polarization spectrum and were investigated in detail. The spectral assignments of the absorption spectrum by Ogawa and Chang [Can. J. Phys. 48, 2455 (1970)] are supported by the current measurements. Although fluorescence excitation and fluorescence polarization profiles normally align precisely, exceptions have been found for many resonances (σu →ndπ, n>3), and comparisons between the line shapes are given for several features.
Thermodynamics of chemical reactions written in terms of homologous series
Authors: Alberty Robert A.
Published: July 2002

In calculating equilibrium compositions of complicated organic systems it is advantageous to aggregate whole homologous series; in fact, chemical reactions can be written in terms of homologous series at a specified partial pressure of ethylene. The standard Gibbs energies of formation, enthalpies of formation, entropies, and heat capacities of homologous series may be calculated as a function of ethylene pressure. The change in standard Gibbs energy of formation at a specified partial pressure of ethylene may, for a reaction written in terms of homologous series groups, be used to calculate an equilibrium constant that can be used to calculate the equilibrium composition. The interpretation of the effect of temperature and pressure on the equilibrium is more complicated because the stoichiometric coefficients are functions of the ethylene partial pressure and temperature.
Vibrational spectra of methylthiirane
Authors: Polavarapu P. L. , Hess B. A. , Schaad L. J. , Henderson D. O. , Fontana L. P. , Smith H. E. , Nafie L. A. , Freedman T. B. , Zuk W. M.
Published: July 2002

Vibrational Raman, infrared absorption, and infrared circular dichroism (VCD) spectra were measured for methylthiirane. Ab inito vibrational frequencies were calculated with a 6-31G basis, and vibrational assignments were suggested by comparing the experimental and theoretical data. These assignments were used for the interpretation of the experimental VCD spectrum of (R)-methylthiirane.
The ionization potentials of CH4 and CD4
Authors: Berkowitz J. , Greene J. P. , Cho H. , Ruscić B.
Published: July 2002

The adiabatic ionization potential of CD4 is measured by photoionization mass spectrometry to be 12.658±0.015 eV, which is 0.05±0.02 eV higher than that of CH4. The difference is attributed to zero point energy differences, rather than different Jahn–Teller stabilization energies.
Measurements of [OH] and [CH3CHO] oscillations and phase relations in the combustion of CH3CHO
Authors: Pugh Spencer A. , Kim Hyung-Rae , Ross John
Published: July 2002

Oscillations of the OH radical concentration in the gas-phase oxidation of acetaldehyde in a CSTR are monitored by means of laser-induced fluorescence. The oscillations of acetaldehyde in this reaction are measured with UV absorption. Light emission, pressure, and temperature oscillations are recorded, and phase relations between these oscillations are presented. In an Appendix, we present a 12-step, five-variable, thermokinetic scheme which uses peracetic acid as the branching agent in the chain-branching mechanism. This model qualitatively reproduces the oscillatory behavior found in this combustion system.
Alkali ion–inert gas potentials
Authors: Patil S. H.
Published: July 2002

Analytic expressions are obtained for the Coulomb and exchange energies for alkali ion–inert gas interaction, incorporating the correct asymptotic behavior of electron densities. We have also introduced suitable damping factors for the polarizability and van der Waals terms. This allows us to obtain accurate values for the interaction energies.
Vibrational relaxation in fluids: Calculations based on a many-body scattering formalism
Authors: Dardi Peter S. , Cukier R. I.
Published: July 2002

We evaluate the density dependence of the rate constant for vibrational to translational energy relaxation of a dilute diatom in a fluid based on an expression we recently obtained. The results are compared with experimental data on H2 relaxation by H2 over a wide range of density. The rate constant is expressed as a time correlation function of the inelastic potential responsible for the vibrational transition, with time evolution occurring on the two potential surfaces corresponding to the initial and final oscillator states. A cumulant expansion method is used to relate this two-state evolution to correlation functions on one surface, and leads to correlation functions of the fluid density relative to the diatom’s location. The relative density correlation function is evaluated approximately by further development of a kinetic theory for the motion of a specific pair of particles in a dense gas. The rate constant is related to the solution of a generalized Smoluchowski equation for the distribution function of the specific pair, under the influence of the potential of mean force and a space and time dependent diffusion coefficient. The dilute gas rate constant is calculated using the cumulant expansion method and compared with the results of conventional atom–diatom scattering. The calculated dense fluid rates without cumulant corrections are compared with the experimental rates. The effect of the cumulant corrections on the dense fluid rates are evaluated and found to be small, which we attribute to the approximate method of their calculation. A detailed discussion of the discrepancy between calculated and experimental rates is given. A comparison of our theory with the independent binary collision model is made.
Comment on effects of elongational flow on the isotropic–nematic phase transition in rod-like systems
Authors: Lee Sin-Doo
Published: July 2002

The phase equilibrium of two different nematic phases in a solution of rod-like molecules subjected to a flow field is found by the application of an iterative solution to the Onsager integral equation for the orientational distribution function. It is shown that there exists no isotropic phase but an additional critical point in the phase diagram when a flow field is applied. It is demonstrated that the nematic ordering induced by a flow field, at a certain critical value of the flow parameter, is always accompanied by a phase transition to a highly ordered nematic phase.
Magnetic properties in terms of localized quantities. VI. Small hydrides, fluorides, and homonuclear molecules of phosphorus and silicon
Authors: Fleischer U. , Schindler M. , Kutzelnigg W.
Published: July 2002

The magnetic susceptibility and the NMR chemical shift tensors (for P, Si, H, and F) are calculated by means of the individual gauge for localized orbitals (IGLO) method for various phosphorus and silicon compounds with single, double, and triple bonds. The choice of appropriate basis sets is studied in detail with the conclusion that on the whole an (11s, 7p, 2d) basis for P in the contraction (7s, 6p, 2d) is required, but for high accuracy three or four sets of d functions are necessary. Somewhat smaller basis sets are sufficient for Si. The susceptibilities and the chemical shifts are obtained as sums of contributions of localized MOs and can hence be interpreted directly. The dependence of the susceptibilities and the chemical shifts on changes of the geometry is also studied.
Coupling of CH stretching and bending vibrations in trihalomethanes
Authors: Wong James S. , Green William H. , Cheng Chi-ke , Moore C. Bradley
Published: July 2002

The vibrational spectra of HCCl3, HCF3, HCCl2F, and HCClF2 have been measured in the vapor from the CH stretching fundamental through to the fifth overtone (i.e., v1=6, where v1 is the number of quanta in the CH stretching mode), using FTIR and photoacoustic spectrometers. Instead of a single strong CH overtone progression, additional strong bands attributable to Fermi-resonant combination tones are prominent in the spectra. The CH stretch is found to be most strongly coupled to the CH bending mode and much less strongly coupled to the heavy atom motions. The resolved band structures are analyzed in the following paper to give quantitative stretch–bend coupling constants for these CH oscillators.
On the 3d 64s2 (5D)−3d 74s1 (5F) separation in Fe
Authors: Bauschlicher Charles W.
Published: July 2002

Full CI calculations to determine the 5D−5F separation in Fe using [5s4p2d], [5s4p3d], and [5s4p2d1f] basis sets show that the single reference SDCI procedure is accounting for most of the differential correlation energy in the 3d and 4s shells. The SDCI separation using a [7s6p4d4f2g] basis set, correlating only eight electrons and accounting for the dominant relativistic effects is 1.25 eV, compared to the experimental value of 0.875 eV. Adding the 3s and 3p electrons to the SDCI treatment reduces the separation to 1.06 eV. It is concluded that the differential effect of higher excitations becomes more important when the 3s and 3p electrons are correlated.
Strong fragment alignment variation with internal state from ICN dissociation at 157.6 nm: Linear regression modeling of CN B 2Σ+ products
Authors: Guest Joyce A. , Webster Frank
Published: July 2002

Dispersed CN B 2Σ+−X 2Σ+ photofragment fluorescence polarization anisotropies measured following ICN dissociation at 157.6 nm vary widely and apparently erratically with emission wavelength, and cannot be converted directly to CN B 2Σ+ rotational alignments because of spectral congestion. A novel linear regression technique is used to extract CN B 2Σ+ populations and rotational alignments from fluorescence emission and polarization anisotropy measurements. We present a flexible procedure which allows one to consider many models for the population and alignment distributions. Criteria are established to identify the best models. The CN B 2Σ+ vibrational branching ratios for v′=0:1:2:3:4 are determined by linear regression to be 0.46:0.25:0.13:0.09:0.07, with a distinct rotational population dependence within each vibrational level. Extracted CN B 2Σ+ alignments for v′=0, 1, 2, and 3 are presented, and these range from −0.31 to nearly 0.2. The alignments vary smoothly with nuclear rotation N′ for each v′, demonstrating that the scatter in the measured polarization anisotropies results from vibrational band overlap at different wavelengths. These results show the largest photofragment alignment variation with vibration and rotation that has been measured following a single-photon dissociation process. A model is presented to estimate partial channel CN B(v′=0) product populations, and a discontinuity in the experimental v′=0 alignment is considered.
Collision-induced intersystem crossing NH(c 1Π)→NH(A 3Π)
Authors: Rohrer F. , Stuhl F.
Published: July 2002

The kinetics and the specific products of the collision-induced intersystem crossing NH(c 1Π,v=0)+M→NH(A 3Π,v)+M were investigated in the ArF laser photolysis of HN3 for various M. The efficiency of the intersystem crossing process was monitored time and spectrally resolved by the enhancement of the NH(A→X) emission. The efficiencies for M=O2, NO, Xe, and N2O are 0.95±0.05, 0.95±0.05, ≤0.15, <0.10, respectively. For M=O2, various vibrational NH(A,v=0, 1, and 2) states are formed with the detailed efficiencies of 0.64, 0.12, and 0.24. We propose that these vibrational states are generated together with O2(a 1Δ,v=4, 2, and 0), respectively. The rotational temperatures for the NH(A,v) products are much colder for M=O2 than for M=NO. For M=Xe, the enhancement of NH(A,v=0) is much larger than that predicted for an efficiency of one and, in the presence of Ar, it is markedly reduced. This large enhancement might be due to a second intersystem crossing process such as NH(b 1Σ+,v≥3)+Xe→NH(A,v=0,1)+Xe. A similar quenchable, but much weaker, additional triplet emission was observed for M=N2O. Absolute rate constants for the quenching of NH(c,v=0) by M=O2, NO, Xe, and N2O were determined at room temperature. Similarly, a value was measured for NH(A,v=2)+O2.
Electron affinity calculations on NH−2, PH−2, CN−, SH−, OH−, Cl−, and F−: Basis sets and direct vs indirect methods
Authors: Ortiz J. V.
Published: July 2002

Electron affinities are calculated with fourth order many-body perturbation theory. Comparisons with renormalized, quasiparticle propagator calculations with the same or comparable basis sets are emphasized. Basis set improvements, including multiple polarization functions, have a great effect on the post-SCF results. The best calculated electron affinities (in eV) and the corresponding experimental values in parentheses are as follows: NH2 0.707 (0.779±0.037), PH2 1.160 (1.271±0.010), SH 2.223 (2.319±0.010), OH 1.764 (1.825±0.002), Cl 3.526 (3.615), and F 3.369 (3.399). Problems with the CN calculations are discussed. Implications of this work for studies of larger systems concern basis set choices and methods of treating electron correlation.