bluuebunny/crossref_metadata_2025 huggingface dataset:
The benzene ground state potential surface. V. Criteria for theoretical modeling of the B2u harmonic force field
Authors: Ozkabak Ali G. , Goodman Lionel , Wiberg Kenneth B.
Published: July 2002

We demonstrate that fundamental frequencies provide a poor criterion of the benzene B2u force field accuracy and that two-photon cross sections of the b2u fundamental bands in the 1B2u↔1A1g electronic transition, which can be directly related to skeletal displacement magnitudes in the two b2u modes, provide an insightful physical criterion of harmonic force field quality. Another valid criterion for force field quality is isotopic frequency shifts combined with the fundamental frequencies. The frequency-generated force field of part II accurately predicts the measured cross sections and isotopic frequency shifts, indicating that the B2u force constants are known to ±0.01 mdyn/Å. These constants are used as benchmark quantities for calibrating theoretically modeled force fields.

A systematic series of ab initio B2u harmonic force fields for ground state benzene using theoretical geometries are generated at Hartree–Fock and correlated second, third, and fourth order (with single, double, triple, and quadruple excitation) Mo/ller–Plesset perturbation theory (MP2, MP3, MP4SDTQ) and configuration interaction theory with all single and double excitation (CISD) levels using basis sets from minimal double zeta to triple zeta plus diffuse and polarized functions. These theoretical models of the B2u force field all provide poor predictions for the three criteria: fundamental frequency accuracy 2%–3%; isotopic frequency shift accuracy 10%–300%; two-photon cross section accuracy 300%–1200% with the sense of isotopic effects on two-photon cross sections in some cases incorrectly predicted. The MP2 calculations, even using the largest basis set, are incapable of meeting any of the criteria, hence higher order approaches to the correlation problem are required. The inadequacies in frequencies, isotopic shifts, and mode forms arise because both the diagonal and off-diagonal force constants are not predicted by ab initio calculations with the sufficient 10−2 mdyn/Å accuracy required for reasonably accurate frequency and intensity predictions. A feature of the ab initio calculations is that carbon and hydrogen displacement phases for the b2u modes are unchanged by the basis set size or correlation level. The unmeasured 13C6D6ν14 two-photon cross section and iosotope frequency shift from 12C6H6 are predicted to be larger than for any of the other D6h symmetry benzenes (∼30% higher than in C6H6 for the former and 72 cm−1 for the latter) by the benchmark field of part II.
Picosecond real-time studies of mode-specific vibrational predissociation
Authors: Semmes David H. , Baskin J. Spencer , Zewail Ahmed H.
Published: July 2002

The vibrational predissociation of several van der Waals complexes of t-stilbene has been studied by directly measuring, in real time, the fluorescence intensity from the initial reactant state and from the individual product states formed in the dissociation process after exciting single vibrational levels of the complex. With the aid of a kinetic model involving sequential processes, the individual rates for intramolecular vibrational redistribution and vibrational predissociation in the overall dissociation process are resolved and distinguished in several cases. In the stilbene–He complex, the dissociation is significantly faster from low energy out-of-plane modes than it is from a higher energy in-plane mode.
Effect of salts on dynamics of water: A Raman spectroscopy study
Authors: Terpstra P. , Combes D. , Zwick A.
Published: July 2002

In this work, we have studied, by means of Raman spectroscopy, water-additives interactions in the case of alkaline halogenides aqueous solutions. We have obtained some parameters describing the evolution of water structure vs concentration or the nature of the added salts. These parameters show, as previously described, a more important effect of anions than cations. Next, the evolution of the dynamical properties of the solution depends on the size of the ions. Moreover, the development of a new band in the isotropic part of the salts solutions spectra is attributed to water–ions interactions involved in the dynamics of hydration shells.
Second and third derivatives of the linear combination of Gaussian type orbitals–local spin density energy
Authors: Fournier R.
Published: July 2002

A practical formulation of the analytical second and third derivatives of the linear combination of Gaussian type orbitals–local spin density energy is presented. The equations obtained hold with little modification for density gradient corrected exchange-correlation functionals. The efficiency and accuracy of future computer implementation of these equations are discussed.
Theoretical spectroscopy of the NO radical. III. Λ doubling and predissociation in the C 2Π state
Authors: de Vivie-Riedle Regina , van Hemert Marc C. , Peyerimhoff Sigrid D.
Published: July 2002

The Λ doubling of the C 2Π state of NO is calculated by considering the heterogeneous couplings (spin–orbit and rotational angular momentum) between the C 2Π and the first three 2Σ+ states plus the homogeneous interaction of the C 2Π with the B 2Π state. All wave functions and energies result from highly correlated configuration interaction wave functions. A transformation from the adiabatic to the diabatic basis is performed by employing the radial coupling between the two 2Π states. The perturbation matrix is solved in the diabatic basis and leads directly to the eigenvectors and eigenvalues of the Λ components. It is found that for J≥3/2 the Λ components are completely mixed and can therefore not be labeled according to their Ω values any more. Vibrational averaging leads to a calculated value of 0.019 cm−1 (J=0.5, v=0) compared to the measured value of 0.016 cm−1 for the Λ doubling. The predissociation process of the C 2Π state is calculated in the adiabatic basis; the mechanism is found to be caused solely by the spin–orbit interaction with the a 4Π state.
Two-center matrix elements for Kratzer oscillators
Authors: Bastida A. , Zúñiga J. , Alacid M. , Requena A. , Hidalgo A.
Published: July 2002

An exact expression for two-center Kratzer oscillator matrix elements of rβ (r is the internuclear distance) is derived. Using the hypervirial-like theorem procedure, several recursion relations among these matrix elements are obtained. It is shown that these relations can be used to calculate recursively two-center Kratzer oscillator matrix elements of rβ and rβd/dr in a very simple way.
Jet spectroscopy and excited state dynamics of benzyl and substituted benzyl radicals
Authors: Fukushima Masaru , Obi Kinichi
Published: July 2002

Benzyl and its p-fluoro and p-methyl derivatives are produced by the ArF laser (193 nm) photolysis of their chlorides in the supersonic free jet. The spectroscopy and excited state dynamics of these radicals are studied by the laser induced fluorescence (LIF) method under the collision free condition. The assignments of vibronic bands are carried out from the LIF excitation and dispersed spectra and the vibrational energies of the D1 state are determined. The excitation spectrum of p-fluorobenzyl shows quite similar vibrational structure to that of p-fluorotoluene up to about 1000 cm−1 from the 000 band, which indicates that D2 of p-fluorobenzyl lies about 1000 cm−1 above D1 and no vibronic coupling exists lower than this energy. On the other hand, benzyl and p-methylbenzyl show very complicated and irregular vibronic structures in excitation spectra, which are not similar to those of toluene and p-xylene. This complication is explained by the D1–D2 vibronic coupling caused by low lying D2 states in these radicals. Time profiles of the emission intensity of p-fluorobenzyl and p-methylbenzyl show single exponential decay and their lifetimes do not indicate significant dependence on vibronic levels. On the other hand, benzyl shows dual exponential decay, which is interpreted by intermediate coupling case behavior.
A truncation/recoupling method for basis set calculations of eigenvalues and eigenvectors
Authors: Bowman Joel M. , Gazdy Bela
Published: July 2002

We describe a new method to truncate and recouple basis functions in general variational calculations based on a direct-product representation of multidimensional wave functions. The method is presented for molecular vibrations; however, the procedure is quite general and can be used in any basis set expansion method. The direct-product Hamiltonian matrix H is decomposed into a block diagonal matrix H0 plus a remainder H1. A new subset of basis functions is obtained by diagonalizing H0. This subset of basis functions is shown to be eigenfunctions of a Hamiltonian in a reduced dimensionality space, ‘‘dressed’’ by the remaining degrees of freedom. These dressed eigenfunctions are then augmented by the component of the original direct-product basis in which H0 is diagonal. The new basis is recoupled using an energy selection criterion, yielding a substantial reduction in the size of the final full Hamiltonian matrix. The method also suggests a generalization of the vibrational self-consistent field method, in which explicit correlation is included in the reduced dimensionality space. An illustrative example of the truncation/recoupling method is given for the vibrational states of HCO, where a major reduction in the order of the Hamiltonian matrix is achieved relative to the conventional direct-product method.
Photodissociation dynamics of Mn2(CO)1 in solution on ultrafast time scales
Authors: Zhang J. Z. , Harris C. B.
Published: July 2002

A study of the photodissociation dynamics of Mn2(CO)10 and the vibrational relaxation of its subsequent photoproducts in solutions has been carried out using picosecond time-resolved laser techniques. The molecule predissociates in less than 2–3 ps after excitation with a 295 nm photon. Two dissociation channels are open for this excitation wavelength, namely, the Mn–Mn bond breaking and the Mn–CO bond breaking, generating internally hot ⋅Mn(CO)5 and Mn2(CO)9, respectively. These two species have a different absorption spectrum in the visible region and are probed independently by varying the probe laser wavelength. The vibrational relaxation of these nascent photoproducts is observed for the first time. In cyclohexane the vibrationally hot Mn2(CO)9 reaches thermal equilibrium with the solvent through two distinct decay channels with time constants of 15 and 170 ps, respectively. The vibrationally cold Mn2(CO)9 then persists for many nanoseconds. The vibrational relaxation is found to be faster in the 2-propanol solution with time constants of 10 and 145 ps. On the other hand, the ⋅Mn(CO)5 species cools down in less than 10 ps and then exists in the solution for many nanoseconds as well. This result indicates that energy transfer from the internally hot ⋅Mn(CO)5 species to the solvent is much faster than from Mn2(CO)9. Comparison is made with Cr(CO)5 in similar solvents.
Elastic constants of the orientationally disordered phase Ib of CCl4 by Brillouin spectroscopy
Authors: Zuk J. , Kiefte H. , Clouter M. J.
Published: July 2002

The technique of Brillouin spectroscopy has been used to determine the full set of adiabatic elastic constants of the orientationally disordered rhombohedral Ib phase of CCl4. The values of the elastic constants at 247.7 K are C11=45.4, C12=29.2, C13=27.3, C14=−1.2, C33=43.3 and C44=9.5 (in units of kbar). This system is elastically quite isotropic and can be closely approximated by hexagonal symmetry. The bulk modulus (33.5 kbar) is almost identical to that of the metastable orientationally disordered cubic Ia phase of CCl4.
Conical intersections in H2Cl+(1A′)
Authors: Kuntz P. J. , Whitton W. N.
Published: July 2002

A 10×10 model Hamiltonian matrix for the 1A′ states of the H2Cl+ molecule in a valence-bond basis is shown to exhibit conical intersections between states 2 and 3 along a line in configuration space (linea diaboli). The points of intersection are located by finding the minimum in the square of the difference of the two eigenvalues and then confirming the nature of the intersection by calculation of the geometrical phase associated with transporting an eigenvector about the point. The locus of the linea diaboli does not correspond to any obvious special geometrical symmetry but rather appears to be related to the charge distributions in the molecular states correlating with the H+HCl+ (A 2Σ+ ) and H+ +HCl(X 1Σ+) asymptotic channels. Some properties of the degenerate eigenstates at the intersections are presented and it is shown how the approximate geometric configurations of the intersection can be found from the eigenvectors of the two appropriate states.
Van der Waals bonding in the lowest electronic states of MgAr, ZnAr, CdAr, and HgAr: Spectroscopic characterization of the b 3Π2 and e 3Σ+ states of the CdAr molecule
Authors: Bennett Robert R. , Breckenridge W. H.
Published: July 2002

Laser-induced fluorescence spectroscopy was utilized to characterize the b 3Π2 and e 3Σ+ states of the CdAr molecule. The CdAr(b 3Π2) state was synthesized by entrainment of metastable Cd(5s5p 3P2 ) atoms (created by laser vaporization of a Cd rod) into a supersonic expansion of Ar gas. Spectroscopic constants, bond lengths, and bond dissociation energies are reported for the CdAr(b 3Π2) and CdAr(e 3Σ+) states. A detailed discussion of van der Waals bonding in all of the low-lying electronic states of the MgAr, ZnAr, CdAr, and HgAr molecules is also presented, including an analysis of the effects of increasing spin–orbit coupling on the 3ΠΩ potential curves.
Intramolecular dynamics. II. Artificial intelligence search evaluation function and treatment of resonance centers for large systems
Authors: Zhang Yongfeng , Marcus R. A.
Published: July 2002

The role of resonance centers in obtaining large size matrices via an artificial intelligence (AI) search is discussed. The results are used to develop for an AI search an evaluation function which takes cognizance of isolated internal resonances in these many-state systems. The effect of later-accepted states on resonance centers is included. This evaluation function and one without a resonance factor are used in Part III of this series. A search is made there to select zeroth-order vibrational states of benzene that are used in a diagonalization treatment of CH overtone spectra. When there are many overlapping resonances, as in that case, a comparison of results obtained with those two types of evaluation function is of particular interest.
Theoretical study of the link between the infrared linewidth of the C–O stretching vibration and the chemisorbed CO–metal bond
Authors: Volpilhac Geneviève , Baba Mohamed Filali , Achard Francis
Published: July 2002

The hopping integrals βam between the molecule and metal atomic orbitals are involved in both the description of the CO–metal chemisorption bond and the calculation of the infrared linewidth L of the C–O stretching vibration (related to an electron–hole pair process). Therefore, some information about the chemisorption bond may be extracted from the experimental values of L. The kinetic energy of the C and O nuclei may be transferred to the electrons using two channels: the 5σ orbital or the (1π, 2π) orbital pair. The βam integrals are assumed to be proportional to k0, the parameter ‘‘describing the chemisorption bond.’’ When k0 is fitted to the experimental values of L, we find k0=0.19 for CO/Pt and k0=0.23 for CO/Ni. In both of these cases, the CO–metal bond and the electron–hole pair process involve only the 5σ orbital.
Some new insights into the old Avrami’s equation
Authors: Bosco E.
Published: July 2002

Melvin Avrami published a series of interesting papers [M. Avrami, J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940); 9, 177 (1941)] on the kinetics of phase change. Since this seminal work half a century ago, Avrami’s theory has found several applications in different physicochemical contexts, the electrochemical phase formation being one such application. In this paper we outline some random coverage problems which arise in the modeling of solid-state transformations at the electrode/electrolyte interface. After briefly reviewing the earlier developments in this area, we go on to show that a new and more general perspective could be provided to Avrami’s problem once we clothe it in the language of geometrical probability and nearest-neighbor statistics. We also show how some of these new insights could remove two of the major restrictions of Avrami’s theory, namely the assumption of a large-sized system and the uniformly random (i.e., Poissonian) distribution of active sites. In particular, we demonstrate the usefulness of Robbins’ theorem and derive a new result with its help, viz., an overlap formula for the Neyman–Scott cluster process. Some interesting connections are also established between order neighbor statistics and overlap formulas.
Adsorption of Na+ and Cl− at the charged water–platinum interface
Authors: Rose Daniel A. , Benjamin Ilan
Published: July 2002

The adsorption of Na+ and Cl− at the charged water–platinum interface as a function of external voltage is investigated by molecular dynamics computer simulation. Generally, although the water structure is significantly affected by a strong external electric field, the structure of the ion–water complex at the surface is much less affected. At electric field values comparable to those found in experimental systems, Cl− is ‘‘contact adsorbed’’ on the metal and is mainly solvated by the water layer adjacent to the metal. In contrast, the small Na+ is solvated equally well by both adsorbed water molecules and water molecules outside the inner layer. At higher electric field values that are close to the upper end of what is believed to exist in electric double layers, both ions lose part of their hydration shell. The dynamic of the ion motion towards the metal up to about one solvent layer from the surface is in reasonable agreement with experimentally known ion conductivities at low electric fields, but it overestimates the ionic mobility at a high electric field. This can be rationalized in terms of the effect of the electric field on the hydration shell residence time. The final step toward contact adsorption at the very high electric field is instantaneous for Na+, but involves a barrier for Cl−.
Nonadiabatic predissociation of CN(A 2Π)–Ne
Authors: Fei Suli , Heaven Michael C.
Published: July 2002

Two predissociation channels were characterized for CN(A 2Π, v=3)–Ne complexes. One was spin–orbit induced (CN(A 2Π1/2, v=3)–Ne→CN(A 2Π3/2, v=3)+Ne), and the other mediated by interstate transfer (CN(A 2Π3/2, v=3)–Ne→CN(X, 2Σ+, v=7)+Ne). The former was approximately 104 times faster than the latter. Symmetry based propensities were evident in the rotational population distributions of the CN fragments.
Gas-phase thermochemistry of VH and CrH
Authors: Chen Yu-Min , Clemmer D. E. , Armentrout P. B.
Published: July 2002

The homolytic bond dissociation energies of the transition-metal neutral hydrides, Do(M–H) (M=V, Cr), are experimentally determined by using guided ion beam tandem mass spectrometry to measure the kinetic energy dependence of the endothermic hydride abstraction reactions of M+ with mono-, di-, and trimethylamine. From the thresholds of these reactions, we derive the 0 K values of Do(V–H)=2.13±0.07 eV and Do(Cr–H)=1.93±0.07 eV. This thermochemistry is compared with theoretical values and previous experimental results.
(He,H2+) dynamics revisited
Authors: Kumar S. , Sathyamurthy N. , Bhalla K. C.
Published: July 2002

The differential cross section for the backward and the forward scattering of the product in (He,H2+) collisions and its dependence on reagent vibration and translation as determined by a three dimensional quasiclassical trajectory study are shown to be in accord with the recently reported experimental results. An investigation of the role of reagent rotation on the differential and integral cross sections for the reaction He+H2+→HeH++H and also on the branching ratio for the two isotopic channels in He+HD+→HeH++D; HeD++H reveals that the dynamical attributes are not strongly dependent on the initial rotational state of the diatom as there is no preferred geometry for the reaction.
Internal rotation of the methyl group in fluorotoluene cations as studied by pulsed field ionization-zero kinetic energy spectroscopy
Authors: Takazawa Ken , Fujii Masaaki , Ito Mitsuo
Published: July 2002

Pulsed field ionization spectra of o-, m-, and p-fluorotoluenes were observed. The spectrum shows a well-resolved structure due to internal rotation of the methyl group in fluorotoluene cations. Observed level energies and relative intensities were reproduced by a one-dimensional periodic potential with a free-rotor basis set. The analysis shows a great increase in the rotational barrier by ionization for all the fluorotoluenes. It was also found that rotational constant of the internal rotation decreases significantly when the barrier height increases drastically by ionization. From the correlation between the barrier height and the internal rotational constant, the increase of the rotational barrier is explained by the increase of the steric hindrance due to the geometrical change by ionization. The vibronic coupling between very high Rydberg states through the methyl rotational motion was suggested by the strong appearance of the a2–a1 forbidden transition in the PFI spectrum.
Selectively breaking either bond in the bimolecular reaction of HOD with hydrogen atoms
Authors: Metz Ricardo B. , Thoemke John D. , Pfeiffer Joann M. , Crim F. Fleming
Published: July 2002

We have determined the branching ratio for the reaction of hydrogen atoms and HOD with either the O–H bond excited or the O–D bond excited. In both cases, the initially excited bond reacts preferentially. Excitation of the third O–H stretching overtone, 4νOH, favors breaking the O–H bond by a factor of ∼200, and excitation of the fourth O–D stretching overtone, 5νOD, favors breaking the O–D bond by a factor of ∼220. Thus vibrational excitation can control the H+HOD reaction to produce either product almost exclusively. A simple model using the calculated wave function for each state and the measured reaction cross section for a particular vibrational excitation predicts the high selectivity observed for the two reactions.
High resolution infrared emission spectra of AlH and AlD
Authors: White J. B. , Dulick M. , Bernath P. F.
Published: July 2002

High resolution infrared emission spectra of aluminum monohydride and monodeuteride have been recorded. Gaseous AlH and AlD were generated by reacting molten aluminum metal with hydrogen and deuterium gas. Approximately 265 AlH lines with v=1→0 to v=5→4 and 470 AlD lines with v=1→0 to v=7→6 are reported. Dunham Yij constants were obtained by fitting the data of each isotopomer separately to the Dunham energy level expression while mass-reduced Dunham Uij constants were obtained from a combined fit of all isotopomer data. A second set of Dunham Uij constants was obtained from a fit where Uij’s with j<2 were treated as adjustable parameters and all remaining Uij’s fixed to values that satisfy the constraints imposed by the Dunham model. Finally, an effective Born–Oppenheimer potential was determined by fitting all the data directly to the eigenvalues of the radial Schrödinger equation containing a parametrized potential function.
Diffusion in zeolites: Anomalous dependence on sorbate diameter
Authors: Yashonath Subramanian , Santikary Prakriteswar
Published: July 2002

Molecular dynamics calculations on sorbate atoms of varying diameters in zeolites A and Y are reported. Rates of cage-to-cage diffusions, rate of cage visits, and diffusion coefficients show unexpected behavior. A generalized parameter has been defined that exhibit a peak in diffusion coefficient around 0.84 for both the zeolites investigated.
Site specific co-adsorption at Pt(335) as probed by infrared spectroscopy: Structural alterations in the CO adlayer under aqueous electrochemical conditions
Authors: Kim Chung S. , Korzeniewski Carol , Tornquist Wade J.
Published: July 2002

Experiments probe the effect of hydrogen co-adsorption on the infrared spectral features of carbon monoxide adsorbed at Pt(335) {Pt(S)-[4(111)×(100)]} under aqueous electrochemical conditions. Using intermediate CO coverages, where it is possible to discern infrared spectral features for CO bound terminally (atop) at edge sites and at terrace sites, the present experiments observe greater alterations in the atop CO population at the step edge compared to the atop CO population on the terrace plane when hydrogen is co-adsorbed under aqueous electrochemical conditions. These findings suggest that hydrogen is preferentially adsorbed at step sites on the Pt(335) surface plane and they coincide with what has been revealed by recent UHV experiments which probed the effect of co-adsorbing oxygen at Pt(335) in the presence of a partial CO monolayer.
Isotropic-nematic transition of hard polar and nonpolar molecules
Authors: Vega Carlos , Lago Santiago
Published: July 2002

A new theory to study isotropic-nematic transition is proposed. This theory requires a good knowledge of the thermodynamic properties of the isotropic phase. It allows to study nematic formation in systems possessing attractive forces. We determine isotropic-nematic equilibria for a number of hard linear models as hard spherocylinders, hard ellipsoids, and hard tangent spheres in a linear configuration. The theory predicts quite nicely the transitions when compared to simulation results. We also study the effect of an ideal dipole or quadrupole on nematic formation. Dipolar or quadrupolar forces favor the presence of a nematic phase although the effect is moderate. However, for large multipole moments no stable nematic phase was found.
Critical dynamics and phase-separation kinetics in dynamically asymmetric binary fluids: New dynamic universality class for polymer mixtures or dynamic crossover?
Authors: Tanaka Hajime
Published: July 2002

It has so far been believed that polymer systems belong to the same dynamic universality class as classical fluids, namely, the so-called model H in the Hohenberg–Halperin notation. However, our recent experimental studies strongly indicate that the behavior of polymer solutions can be explained by none of the conventional dynamic universality classes at least in the practical sense. Topological characteristics of polymer chains induces the slow molecular motion of polymer and the viscoelastic effect. The asymmetry in molecular dynamics between polymer and solvent leads to the strong kinetic coupling between the stress field and the order parameter. This causes the viscoelastic suppression of the order parameter fluctuation for equilibrium critical dynamics and unusual phase separation having a viscoelastically driven morphology for unstable states. The relaxational nature of viscoelastic effect violates the selfsimilarity of the growing pattern. A new concept of dynamic symmetry should be introduced in addition to the static, composition symmetry.
Comparison of infrared absorption intensities of benzene in the liquid and gas phases
Authors: Bertie John E. , Keefe C. Dale
Published: July 2002

This paper presents a comparison of the absolute infrared absorption intensities in the liquid and gas phases for the four infrared active fundamentals of benzene. In Herzberg’s notation these are ν12 (∼3070 cm−1), and ν4 (∼675 cm−1). Published data are used, including the recently published spectra of liquid benzene that have been accepted by the International Union of Pure and Applied Chemistry as secondary intensity standards. The present results agree qualitatively with the conclusions drawn in 1970 that the intensity Aj of ν12 is much smaller for the liquid than for the gas, and those of ν13, ν14, and ν4 are all larger for the liquid. The inclusion of measurements made since 1970 should make the quantitative results reported here the most reliable. However, two quite different values have been reported in the 1980’s for the intensity of ν14 in the gas phase, and both are considered. The comparison for ν14 is also complicated by the existence of weak bands in the spectrum of the liquid that are not observed in that of the gas. It is noted in this work that the traditional comparison, of the areas under the molar absorption coefficient spectra, Aj, for the gas and liquid through the Polo–Wilson equation, has the drawback that the ratio expected if the dipole moment derivative is unchanged is different for each band as well as for each liquid.

A much more convenient ratio, that equals unity for all bands of all liquids under the traditional assumptions, is proposed through the imaginary molar polarizability spectrum of the liquid. The magnitudes of the transition moments and the dipole moment derivatives with respect to the normal coordinates under the double harmonic approximation are calculated from the measured intensities for the gas and liquid phases. It is found that the dipole moment derivative of ν12 is 24% smaller in the liquid than in the gas and that of ν13 is 18% larger. The dipole moment derivative of ν4 is unchanged by condensation. The change in the dipole moment derivative of ν14 is not clear, because of the uncertainty in the gas phase intensity and because of the uncertain origin of the intensity of the additional bands in the liquid.
A theoretical study of the CH3+C2H2 reaction
Authors: Diau Eric W. , Lin M. C. , Melius C. F.
Published: July 2002

The rate constants for the formation of various products in the CH3+C2H2 reaction have been computed by multichannel RRKM calculations using the molecular and transition-state parameters predicted by the BAC-MP4 method. The results of the calculations agree quantitatively with experimental data obtained under varying conditions: T=300–2200 K, P=30–2500 Torr. At low temperatures (T<1300 K), the CH3+C2H2 reaction is dominated by the addition-stabilization process producing CH3C2H2. Under high-temperature (T≳1400 K) and atmospheric-pressure conditions, the reaction occurs primarily by the CH3-for-H displacement process producing CH3C2H, a likely source of the C3H3 radical (which has recently been shown to be a key precursor of C6H6 in hydrocarbon combustion reactions).
The vibrational spectra of krypton and xenon difluoride: High-resolution infrared studies and ab initio calculations
Authors: Bürger H. , Kuna R. , Ma S. , Breidung J. , Thiel W.
Published: July 2002

Fourier transform infrared spectra of KrF2, XeF2, and monoisotopic 136XeF2 have been recorded in the ν3 and ν1+ν3 ranges with an effective resolution of 0.003–0.007 cm−1. About 10 000 rovibrational lines belonging to cold bands and to hot bands with ν1, ν2, 2ν2, and ν3 as lower levels have been assigned and fitted. The high-resolution results from this work and from two previous studies provide a rather complete set of precise spectroscopic constants and accurate ground-state and equilibrium geometries for both molecules. In the case of 84KrF2, r0=188.2821(9) pm supersedes previous incorrect r0 values, and re=187.6930(23) pm represents the first determination of the Kr–F equilibrium distance. Ab initio calculations employing effective core potentials and polarized double-zeta basis sets have been carried out at the following levels: self-consistent-field (SCF) theory, the Mo/ller–Plesset second order perturbation theory (MP2), and coupled cluster theory with single and double excitations (CCSD) and a perturbational treatment of triple excitations (CCSD(T)). Pronounced correlation effects are found, especially for KrF2. The agreement between the correlated theoretical and the experimental results is generally quite good. A theoretical analysis clarifies the origin of the positive α2 vibration–rotation coupling constants which have been observed for the bending vibrations in both molecules. Reliable harmonic and anharmonic force fields are presented for KrF2 and XeF2.
A graphical unitary group approach to study multiplet specific multichannel electron correlation effects in the photoionization of O2
Authors: Stratmann R. E. , Lucchese Robert R.
Published: July 2002

We have implemented an efficient multichannel configuration–interaction complete-active-space (MCCI-CAS) approximation to study electron–correlation effects in molecular photoionization. This approach is based on the graphical unitary group approach (GUGA) for computing matrix elements of the Hamiltonian and includes target relaxation, correlation, and polarization as well as correlation due to coupling between different asymptotic scattering channels. The statistical rule, which partitions the total cross section into multiplets by simple spin statistics, is easily derived in this formalism. The scattering equations are solved using the Schwinger variational method. We present multiplet specific results of a detailed MCCI-CAS Schwinger study of the photoionization of molecular oxygen in the photon energy region of 12.3–20.4 eV, including up to four coupled electronic channels. Our results show the importance of using correlated target states. We have obtained all of the autoionization structure near threshold that has been assigned experimentally. In addition, we predict structure not yet resolved by experiment.
Photodissociation of ozone at 193 nm by high-resolution photofragment translational spectroscopy
Authors: Stranges Domenico , Yang Xueming , Chesko James D. , Suits Arthur G.
Published: July 2002

The photodissociation of ozone has been studied at 193 nm using high resolution photofragment translational spectroscopy. The results show six distinct peaks in the time-of-flight spectra for the O2 product and its momentum-matched O atom counterpart. The translational energy distributions determined from the time-of-flight spectra reveal the production of a range of electronic states of the photofragments. The product electronic states were identified based on the translational energy distributions, with the aid of state-resolved imaging experiments by Houston and co-workers. The results reveal the production of a substantial yield of highly excited triplet states of O2, recently suggested to play an important role in the stratospheric ozone balance. In addition, peaks corresponding to O2(a 1Δg) and O2(b 1Σg+) were observed, the latter confirming a previous report [A. A. Turnipseed et al., J. Chem. Phys. 95, 3244 (1991)]. Evidence was seen for a small contribution from the triple dissociation O3→3O(3P), and insight into the dissociation dynamics for this process was inferred from the translational energy distributions. Branching fractions and angular distributions were measured for all channels. The latter were found in general to yield negative β parameters, in contrast to what is seen at longer wavelengths.
Comment on: ‘‘The conservation of quantum zero-point energies in classical trajectory simulations’’ [J. Chem. Phys. 102, 1705 (1995)]
Authors: Schlier Christoph
Published: July 2002

Quasiclassical trajectory calculations are deficient in that they do not yield correct zero-point energies of products. Arguments are given that this cannot be repaired by the exclusion of all phase space in which any mode has an instantaneous energy below its local zero-point limit.
Molecular dynamics study of cluster evolution in supersaturated vapor
Authors: Zhukhovitskii D. I.
Published: July 2002

Behavior of an argonlike cluster in supersaturated vapor at constant temperature and pressure is simulated. In contrast to the results of conventional microcanonical ensemble simulations, instability of cluster size is observed (unlimited growth or complete evaporation). This defines cluster critical size, which is noticeably larger than that predicted by the classical nucleation theory. Analysis of cluster collective vibrational spectra shows that its evaporation is intimately connected with spontaneous emergence of the lowest modes of breathing vibrations. The cluster phonon spectrum resembles that of a strange attractor.
Multireference configuration interaction studies on metastable states of the dication BN2+
Authors: Mawhinney Robert C. , Bruna Pablo J. , Grein Friedrich
Published: July 2002

Multireference CI calculations predict fourteen states of BN2+ to be quasibound, an uncommonly large number for a first-row diatomic, confirming the important role played by the electropositive B atom in stabilizing molecular dications. About two-thirds of the metastable potentials have dissociation barriers (Deff) between 0.59 and 2.25 eV, accommodating several vibrational levels and therefore being kinetically stable. The ground state X 3Σ−, however, might be difficult to study experimentally because it is only weakly bound (Deff=0.23 eV), and its formation via ionization of BN or BN+ has unfavorable Franck–Condon factors (FCF). The 1 5Σ− state is the best candidate for detecting BN2+: Its barrier is the highest (Deff=2.25 eV), sustaining about 30 vibrational levels (with tunneling lifetimes τTυ≊∞ for υ<20), and the ionization FCFs are favorable. The 1 1Δ state might also be detectable since its properties are similar to those of 1 5Σ−. Near equilibrium, most metastable states are described by the configurations 3σ24σ5σ1π2 and 3σ24σ1π3, both having charge distributions B2+N. The adiabatic ionization potential into BN2+ (X 3Σ−) is 21.4 eV for ionization from BN+ (X 4Σ−) and 32.9 eV from BN(X 3Π). The corresponding IPs into 1 5Σ− lie 1.12 eV higher.
Herringbone structure in two-dimensional single crystals of cyanine dyes. I. Detailed structure analysis using electron diffraction
Authors: Kirstein S. , Steitz R. , Garbella R. , Möhwald H.
Published: July 2002

The crystalline structure of two-dimensional aggregates of different carbocyanine molecules was investigated in detail by means of electron diffraction. The aggregates are formed by electrostatic adsorption of anionic dye molecules from an aqueous solution at a positively charged ammonium lipid monolayer. From the diffraction pattern we deduce a herringbonelike arrangement of the dye molecules as described by a centered, rectangular unit cell containing two identical molecules. The aggregate structures of the systems investigated here differ only by the mutual orientation of the molecules and the axis ratios of the unit cell. For further optical studies we determine the angle α between the main axes of the differently oriented molecules with very high precision. We calculate electron diffraction intensities of several structures which are simulated on the computer and compare them to experimental data. We observe that the dye aggregates are aligned to one of the crystal axes of the lipid lattice.
The long-range potential of the K2 X 1Σ+g ground electronic state up to 15 Å
Authors: Amiot Claude , Vergès Jean , Fellows Carlos E.
Published: July 2002

Titanium sapphire laser induced fluorescence spectra of the A 1Σ+u→X 1Σ+g electronic system have been recorded at high resolution by Fourier transform spectroscopy. Ground state vibrational levels are observed up to v=81 corresponding to an internuclear distance of 15.4 Å and to 99.96% of the potential well depth. A long range study of the potential energy curves (RKR and IPA) allowed the determination of the coefficients of the dispersion energy (multipolar expansion representation) and of the exchange energy (exponential representation). The dissociation energy is found to be 4450.75±0.15 cm−1.
Toward preresonant impulsive Raman preparation of large amplitude vibrational motion
Authors: Smith T. J. , Cina J. A.
Published: July 2002

This article investigates a new approach to the optical generation of large-amplitude coherent molecular vibrations in condensed media. On the basis of analytical results using pulse propagators in the classical Franck approximation, we are led to investigate the efficacy of driving vibrational motion in the electronic ground state by impulsive stimulated Raman scattering with a timed sequence of electronically preresonant femtosecond laser pulses. Numerically exact computations are performed on a model system of dilute molecular Iodine in a low-temperature host crystal. Vibrational relaxation is incorporated via Redfield theory. The results indicate that under a variety of conditions, chemically significant (greater than 0.1 Å) displacements can be produced in a Raman active mode with a fair measure of control over wave packet spreading, and without substantial population loss due to electronic absorption.
Temperature dependence of vibrational relaxation of N2 by O2 in liquid N2 along the coexistence curve
Authors: Abdel-Halim Hamzeh M.
Published: July 2002

The temperature dependence of vibrational relaxation rates of N2(υ=1) by O2 in liquid N2 has been studied at several temperatures along the coexistence curve between 80 and 120 K. A small amount of CO was added to the N2–O2 mixture as a pump and a probe. A CO laser was used to excite CO in solution and its fluorescence was monitored to obtain the rate of vibrational energy transfer. The liquid-phase rate constants kl were compared with the gas-phase constants kg at the same temperatures and found to be essentially equal. This result is in reasonable agreement with the predictions of the isolated binary collision model.
Reactive O2(v⩾26) as a source of stratospheric O3
Authors: Toumi Ralf , Houston Paul L. , Wodtke Alec M.
Published: July 2002

The reaction of vibrationally excited O2 (v≥26) with ground-state O2 has been proposed as a source of stratospheric O3. The O2 (v≥26) yield from O3 photolysis has now been determined at 193 and 226 nm. Here we examine the wavelength dependence of the new mechanism. We find that the new O3 production is most sensitive to the O2 (v≥26) yield near 220 nm. Shorter and longer wavelengths are less important for this new production mechanism.
Pore size dependence of the dipolar-correlation effect on the stimulated echo in liquid crystals confined in porous glass
Authors: Grinberg Farida , Kimmich Rainer
Published: July 2002

The dipolar-correlation effect on the stimulated echo of nematics probes (a) the order parameter and (b) the distribution of the director fluctuations. This effect was employed for the study of orientational director fluctuations in a nematic liquid crystal confined in Bioran porous glasses with mean pore diameters of 30, 70, and 200 nm. No macroscopic preferential orientation of the director could be detected in the confined material. The reason is, that the local director is oriented by surface interactions rather than by the magnetic field. As already shown in our previous work, the attenuation of the dipolar correlation quotient (stimulated-echo amplitude divided by the primary echo amplitude) is able to monitor director fluctuations in the time scale of the pulse sequence. The echo attenuation rate exhibits a strong dependence on the pore size. It is determined by the mean squared fluctuation of the dipolar coupling constant and characterises the distribution of the director fluctuation modes. The mean squared fluctuation decreases with decreasing pore size. The dependence on the inverse pore diameter decays exponentially and suggests a critical mean pore size of about 120 nm for the crossover to bulk behavior. The dipolar-correlation effect thus may be suitable for the determination of mean pore diameters in porous materials.
Diffusion and vibrational relaxation of a diatomic molecule in the pore network of a pure silica zeolite: A molecular dynamics study
Authors: Demontis Pierfranco , Suffritti Giuseppe B. , Tilocca Antonio
Published: July 2002

The vibrational relaxation and the diffusion of diatomic molecules in the zeolite silicalite have been studied through molecular dynamics simulations in the microcanonical statistical ensemble. The adopted model accounts for the vibrations of the framework and sorbed atoms using a harmonic potential for the silicalite and a Morse potential for the diatomic molecule. The results show that the framework favors the relaxation of diatomics oscillating at frequencies near to its characteristic vibrational frequencies, leading in such cases to lower relaxation times and to an increasing in the energy exchanged per collision. The diffusion of a two-site oscillating molecule representing ethane has been also investigated; the diffusion coefficient and the heat of adsorption agree very well with the experimental data. Arrhenius parameters for the diffusion have been calculated, and some insights into the diffusion mechanism have been obtained from log–log plots and by inspection of the distribution of the ethane molecules in the silicalite channels. Therefore the simplified model adopted seems to adequately describe the diffusive motion and the guest–host energy exchanges, and it could be useful in order to study simple bimolecular reactions in zeolites.
Nonlinear electro-optical response. II. Steady state dielectric relaxation in coupled fields
Authors: Déjardin J. L. , Déjardin P. M. , Kalmykov Yu. P.
Published: July 2002

Nonlinear dielectric response of polar and polarizable molecules dissolved in a nonpolar solvent arising from a weak ac field superimposed on a strong dc bias field are established. The general case when both permanent and induced dipole moments are taken into account is considered. By expanding the expectation value of the first Legendre polynomial as a power series in the ac field strength up to the second order, we find two distinct components in ω and 2ω. Matrix continued fraction methods are used in order to express exactly the solution of the infinite hierarchy of the five-term differential recurrence relations for the ensemble averages of the Legendre polynomials (relaxation functions). The spectra of the real and imaginary parts of the first and second order complex dielectric response functions are presented in figures in order to show the essential differences between the linear and the nonlinear dielectric responses. The analytical expressions so obtained can be checked in so far as each component can be separated experimentally.
Electronic dephasing in nonpolar room temperature liquids: UV photon echo pulse duration dependent measurements
Authors: Zimdars David , Francis R. S. , Ferrante C. , Fayer M. D.
Published: July 2002

The homogeneous dephasing times, T2, were obtained for the nonpolar chromophore diphenyl acetylene (DPA) dissolved in the room temperature nonpolar solvents 2-methyl pentane (2MP) and cyclohexane. The dephasing times were determined by comparing the pulse duration dependent resonant enhancement of the total two pulse four wave mixing signal to a numerically evaluated theory. Data was taken with 80 and 400 fs transform limited pulses at 300 nm, the electronic origin of DPA in the two solvents. In DPA/2MP, T2=120 fs and in DPA/cyclohexane, T2=500 fs. The analysis required concentration and power dependent measurements to quantitatively determine the resonant enhancement of the signal arising from the addition of DPA to the solvents above the nonresonant solvent only signal. Fundamental experimental difficulties inherent in performing UV femtosecond two pulse photon echoes, in particular the competition with nonresonant signal, are discussed. An efficient numerical algorithm for calculating photon echo decay curves with realistic pulse envelope is described.