bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-induced fluorescence of radicals produced in reactions of halogenated ethylenes with atomic oxygen
Authors: Washida Nobuaki , Furubayashi Masashi , Imamura Takashi , Bridier Isabelle , Miyoshi Akira
Published: July 2002

Three new laser-induced fluorescence spectra have been observed when reacting oxygen atoms with halogenated ethylenes such as CHFCF2, CF2CHCl, CH2CCl2, CH2CHCl, and CHClCHCl. These new spectra are similar to those reported previously for the vinoxy CH2CHO and CH2CFO radicals, which suggests that they can be assigned to other halogenated vinoxy-type radicals. Recently Williams and Fleming assigned one of these LIF spectra to the FCO radical; additional experiments have been done to address this conflicting assignment.
Velocity modulated laser absorption spectroscopy of TiCl+
Authors: Kaledin Leonid A. , Heaven Michael C.
Published: July 2002

Velocity modulated laser absorption spectrum of the TiCl+ molecular ion was recorded in the yellow-green spectral region. The ions were generated in a 25 kHz ac discharge through flowing samples of TiCl4 in Ar. The [17.9]3Δ−X3Φ and [17.9]3Δ−(1)3Δ band systems of TiCl+ were recorded and analyzed. We report the results of a deperturbation analysis of the X3Φ and (1)3Δ states. A multiconfiguration ligand field calculation was used to account for the observed electronic states of TiCl+.
Spectroscopy and nonadiabatic predissociation of CN–Ne
Authors: Lawrence W. G. , Chen Yaling , Heaven Michael C.
Published: July 2002

The spectroscopy and predissociation dynamics of CN–Ne were investigated using a variety of laser excitation techniques. Properties of the A 2Π state (vibrational levels v=2, 3, and 4) were characterized through studies of the A–X system. Both spin–orbit components of CN(A)–Ne were subject to predissociation. The upper component (Ω=1/2) was predissociated by rapid spin–orbit relaxation (τ≈6 ps, no vibrational dependence). The lower component (Ω=3/2) was predissociated by the nonadiabatic internal conversion process, CN(A 2Π3/2,v)–Ne→CN(X 2 Σ+,v+4)+Ne. Rates for predissociation by internal conversion were found to be exponentially dependent on the energy gap between the initial and final CN levels. These rates were relatively slow, permitting observation of rotationally resolved spectra for bands associated with the monomer Ω=3/2 v=3 and 4 levels. Double resonance techniques were used to simplify the spectra and establish ro-vibronic assignments. Details of the intermolecular potential-energy surfaces were derived from these data. CN final state population distributions resulting from spin–orbit and internal conversion predissociation were characterized. For the former, excess energy was channeled into rotational excitation of CN, and levels of−parity were preferentially populated. The excess energy in predissociation by internal conversion was released primarily to translational recoil. In the accompanying paper, Yang and Alexander present ab initio potential surfaces for CN–Ne. From these surfaces they predict ro-vibronic energies and predissociation rates for levels associated with A, v=3. Results that depended on the A state surface alone were found to be in good agreement with experiment. Comparison of the internal conversion predissociation rates indicates that the ab initio calculations underestimated the coupling between the A and X states.
Semiclassical approximations to golden rule rate constants
Authors: Skinner J. L.
Published: July 2002

Fermi’s golden rule gives an expression for state-to-state rate constants that involves the Fourier transform of a quantum mechanical time correlation function. It is often convenient to evaluate such an expression semiclassically, by calculating the correlation function classically. For an arbitrary quantum subsystem coupled linearly (in the bath coordinates) to a harmonic bath, I show that the semiclassical result must be multiplied by a certain “quantum correction factor” in order to obtain the exact result. This generalizes the recent work of Bader and Berne, which was for the overall vibrational relaxation rate of a harmonic oscillator bilinearly coupled to a harmonic bath.
Crossed beam reaction of atomic carbon, C(3Pj), with the propargyl radical, C3H3(X 2B2): Observation of diacetylene, C4H2(X 1Σg+)
Authors: Kaiser R. I. , Sun W. , Suits A. G. , Lee Y. T.
Published: July 2002

The reaction of ground-state carbon, C(3Pj), with the propargyl radical, C3H3(X 2B2), is investigated at an average collision energy of 42.0 kJmol−1 employing the crossed molecular beams technique and a universal mass spectrometric detector. The laboratory angular distribution and time-of-flight spectra of the C4H2 product are recorded at m/e=50. Forward-convolution fitting of our data reveals the formation of diacetylene, HCCCCH, in its X1Σg+ electronic ground state. The reaction dynamics are governed by an initial attack of C(3Pj) to the π-electron density at the acetylenic carbon atom of the propargyl radical, followed by a [1,2]-hydrogen migration to the n-C4H3 isomer. A final carbon–hydrogen bond rupture yields atomic hydrogen and diacetylene through a tight exit transition state located 30–60 kJmol−1 above the products. This first successful crossed molecular beams study of a reaction between an atom and a free radical marks the beginning of the next generation of crossed beams experiments elucidating the formation of molecular species in combustion processes, chemical vapor deposition, in the interstellar medium, outflows of carbon stars, and hydrocarbon-rich planetary atmospheres via radical–radical reactions.
A simple physical picture for quantum control of wave packet localization
Authors: Cao Jianshu , Wilson Kent R.
Published: July 2002

Based on weak field quantum control theory, a semiclassical approximation relates the characteristic parameters of the tailored light field to corresponding classical dynamical quantities and thus reveals the underlying physical basis of wave packet focusing. A coordinate-dependent two-level-system approximation is employed to further analyze the molecular dynamics induced by short laser pulses, thus leading to a simple interpretation of the observed correlation between the pulse chirp and vibrational focusing and defocusing. Though our study is presented in the context of quantum control, the conclusions are general, providing an intuitive picture of the quantum coherence of light–matter interaction and a guideline for the design of tailored laser fields.
Nonadiabatic coupling of the 3p Rydberg and ππ* valence states of acetone
Authors: McDiarmid Ruth , Xing Xing
Published: July 2002

The 3p Rydberg region of the spectra of acetone and acetone-d6 has been studied by reson-antly enhanced multiphoton ionization and photoacoustic spectroscopies. Differences between the spectra of cold and room temperature samples, between REMPI and PA spectral measure-ments, and between the laser power dependences of the different 3p←X̃ origins have been deduced to arise from a nonadiabatic coupling of the A1 3p Rydberg and A1ππ* states of acetone. The coupling is proposed to arise from a seam of conical intersection between these two A1 states on the CO stretch–C2CO pyramidalization plane. An analogous seam is proposed to exist between the A1 3d Rydberg and A1 ππ* states.
Dissociative electron attachment cross section to CHCl3 using a high resolution crossed beams technique
Authors: Matejcik S. , Senn G. , Scheier P. , Kiendler A. , Stamatovic A. , Märk T. D.
Published: July 2002

Using a crossed electron-molecule beam ion source in combination with a quadrupole mass spectrometer we have studied the electron energy dependence of the dissociative attachment process CHCl3+e→Cl− at electron energies from about 0 to 2 eV and in a target gas temperature range of about 300–430 K. The energy resolution and working conditions of this newly constructed crossed beams machine have been characterized using CCl4 as a test and calbrant gas. Utilizing the improved energy resolution of the present experimental setup (which allows measurements with FWHM energy spreads down to below 5 meV) it was possible to determine the accurate shape and magnitude of the cross section function in the low-energy range. This leads to the conclusion that between an electron energy of about 20 and 130 meV the reaction proceeds via deBroglie s-wave capture, whereas at higher energy (above about 0.4 eV) autodetachment plays a significant role. Moreover, the present measurements allow us to clarify previously reported differences in the absolute cross section, the number of peaks and in the energy position of these peaks. Finally, by analyzing the measured strong temperature dependence of the cross section close to zero electron energy the activation barrier for this dissociative attachment was determined to be 110±20 meV in good agreement with thermochemical data from swarm experiments performed under thermal equilibrium. Taking into account the present results it is also possible to discuss the mechanism for the existence of the second peak.
Structure and dynamics of molecular ions in clusters: I2− in flexible CO2
Authors: Ladanyi Branka M. , Parson Robert
Published: July 2002

The structures and dynamics of I2− molecular ions embedded in clusters of flexible solvent molecules are studied using molecular dynamics simulation. The potential model extends the work of Papanikolas et al. [J. Chem. Phys. 102, 2452 (1995)] by taking into account the low-frequency bending vibrations of the solvent molecules. Results are presented for flexible CO2 and for a hypothetical solvent in which the bending force constant of CO2 has been decreased by a factor of 5. The structure and the vibrational relaxation dynamics of I2− in flexible CO2 differ only slightly from what was seen in rigid CO2. In “hyperflexible” CO2, however, the solute becomes strongly polarized even at its equilibrium geometry, and the cluster structures are highly asymmetric, demonstrating that the localizing solvation forces are able to overcome the delocalizing chemical bonding interactions. The pathways for vibrational relaxation are also found to be distinctly different in the flexible and hyperflexible solvent.
Photodissociation of C–H and C–O bonds of p-methoxytoluene and p-methoxybenzyl alcohol in solution
Authors: Fujiwara M. , Toyomi K.
Published: July 2002

The photodissociation of p-methoxytoluene and p-methoxybenzyl alcohol at 266 nm in n-heptane solution is studied by nanosecond fluorescence and absorption spectroscopy. The formation of a p-methoxybenzyl radical is identified by its fluorescence which is induced by excitation at 308 nm. The yields of the radical are of the order of ∼10−3 for dissociation of p-methoxytoluene and p-methoxybenzyl alcohol. The growth rate of 1.5×108 s−1 for the radical is equal to the decay rate of (1.5±0.3)×108 s−1 for the precursor fluorescence in dissociation of p-methoxytoluene, whereas the growth rate of >1.0×109 s−1 for the radical is much faster than the decay rate of (1.8±0.3)×108 s−1 for the precursor fluorescence in dissociation of p-methoxybenzyl alcohol. The formation of the radical depends linearly on the photolysis pulse fluence for dissociation of p-methoxytoluene and p-methoxybenzyl alcohol. The data show existence of two distinct dissociation channels. p-Methoxytoluene dissociates from thermally equilibrated levels of the S1 state after vibrational relaxation, whereas p-methoxybenzyl alcohol dissociates from vibrationally excited levels of the S1 state in competition with vibrational relaxation. The difference of these channels is explained on a model of electronic coupling between the precursor and product states in the geometry where the C–H and C–O bonds are stretched in a plane perpendicular to the benzene rings. For p-methoxytoluene, the S1 state does not correlate adiabatically to the ground state of the C–H bond fission products, so intersystem crossing or internal conversion precedes dissociation. For p-methoxybenzyl alcohol, avoided crossing between the ππ* (benzene) configuration and the np(O)σ*(C–O) repulsive configuration results in the adiabatic potential-energy surface which evolves to the ground state of the C–O bond fission products allowing rapid dissociation.
The predissociation mechanisms of the e 1Πu and the b′ 1Σu+ states of N2
Authors: Buijsse B. , van der Zande W. J.
Published: July 2002

A theoretical analysis is given of the photofragment anisotropy of long-lived vibrational states as a function of the rotational level and as a function of the predissociation mechanism. The anisotropy of the lower rotational levels is a strong analytical tool for the identification of the electronic symmetry in the final continuum state. Experiments have been performed on the (4pπ)e 1Πu(v=0) Rydberg state and b′ 1Σu+(v=16) valence state in molecular nitrogen using fast beam translational spectroscopy. The rotational levels of the e 1Πu state yield both N(4S)+N(2P) and N(4S)+N(2D) products. We found different angular distributions for S4+P2 and S4+D2 fragments, although originating from the same rotational level. The observed anisotropy parameters, also called β parameters, have been interpreted and point to the presence of complex predissociation pathways involving mixing with known nearby bound and continuum states. The b′ 1Σu+(v=16) state produces dominantly S4+D2 fragments. We give a suggestion for the most likely dissociation mechanism based on the observed angular distribution.
Van der Waals potentials of He2, Ne2, and Ar2 with the exchange energy calculated by the surface integral method
Authors: Kleinekathöfer U. , Tang K. T. , Toennies J. P. , Yiu C. L.
Published: July 2002

A simple semiempirical potential for two-body multielectron systems is developed. The repulsion is obtained from the exchange energy that is calculated with the surface integral method. The main component of the attraction comes from the second-order polarization energy given by the damped dispersion series. The small contributions of the first-order polarization energy and the overlap integrals to the van der Waals potential are examined. Without any adjustable parameters, this theory is shown to give accurate potential curves for the He2, Ne2, and Ar2 systems. By absorbing the first-order polarization energy into the exchange energy expression and neglecting the small contribution of the overlap integrals, this theory reduces to the successful Tang–Toennies potential model.
Electronic spectroscopy and molecular structure of jet-cooled diphenylamine and diphenylamine derivatives
Authors: Tretiakov I. V. , Cable J. R.
Published: July 2002

Vibrationally resolved electronic spectra of diphenylamine, three deuterated isotopomers, and both para-methyl and para-fluoro substituted derivatives have been recorded in a supersonic jet expansion using resonantly enhanced two-photon ionization. Analysis of these spectra, supported by ab initio calculations, has been used to determine the gas phase structure of diphenylamine. In both the ground and first excited singlet states, an effective C2 symmetry structure is found in which the nitrogen atom is in a planar configuration and the phenyl rings adopt equal torsional angles. Calculations suggest that large-amplitude motion along the nitrogen inversion coordinate is possible in the ground electronic state. Isotopic substitutions have been used to assign the two low-frequency Franck–Condon active modes to different admixtures of symmetric phenyl torsion and bending about the central nitrogen. Electronic excitation to the S1 state results in a decrease in the phenyl torsional angles of 7.4° and an increase in the C–N–C bond angle of 4.0°. While spectra of both the para mono- and dimethyl derivatives as well as the para-diflouro derivative indicate that little change occurs in either the physical or electronic structure of the basic chromophore, the spectrum of the monosubstituted para-fluoro derivative is indicative of a substantial perturbation to both.
Evidence of rotational autoionization in the threshold region of the photoionization spectrum of CH3
Authors: Litorja Maritoni , Ruscic Branko
Published: July 2002

The photoionization spectrum of the threshold region of CH3 equilibrated at room temperature has been recorded and compared to the zero electron kinetic energy (ZEKE) spectrum of Blush et al. [J. Chem. Phys. 98, 3557 (1993)]. The ionization onset region is at ∼70 cm−1 higher energy than previous high-temperature photoionization work [Chupka and Lifshitz, J. Chem. Phys. 48, 1109 (1967)], but still ∼34 cm−1 lower than that implied by invoking only direct ionization. The residual discrepancy can be accounted for by including fully allowed quadrupole-induced and partially allowed dipole-induced rotational autoionization, thus making the observed onset completely congruous with the ZEKE ionization potential. In addition, the fragment appearance potential of CH3+ from CH4 was redetermined by accurate fitting as AP0(CH3+/CH4)=14.322±0.003 eV. With the very precise ZEKE ionization potential, this yields the best current value for the bond dissociation energy in methane, D0(H–CH3)=4.484±0.003 eV=103.40±0.07 kcal/mol (104.96±0.07 kcal/mol at 298 K).
Controlling nonpolar solvation time scales: An instantaneous normal mode viewpoint
Authors: Kalbfleisch T. S. , Ziegler L. D.
Published: July 2002

The effects of temperature, solvent mass, ground-state solute–solvent interaction potential, and difference potential on the time scale for the decay of an electronic transition energy gap correlation function (ECF) are investigated within the context of a linear instantaneous normal mode (INM) model of fluid dynamics. This correlation function is also known as the solvation autocorrelation. The system described here is the B-state transition of methyl iodide in the nonpolar solvents argon and methane. The required ground- and excited state interaction potentials have been determined in previous experimental spectroscopic studies. The solvation time scale is of the order of 100–200 fs for solvent densities ranging from ρ*=0.08 to ρ*=0.8. The molecular properties responsible for determining the solvation time scale of this nonpolar system are delineated here. Via this INM approach, the nonpolar solvation time scale can be approximated by the ratio of a characteristic solute–solvent separation distance scaled by the shape of the difference potential and the inertial velocity of the solvent particles. The time scale of solvation is found to be independent of the magnitude of the difference potential (solute–solvent coupling strength). Thus by changing the coupling strength and leaving the shape of the difference potential constant, the corresponding electronic absorption spectrum passes from the inhomogeneous to the motional narrowing limit. This is due to the change in the decay time of the static dipole correlation function and not to any change in system dynamics. Only very modest changes in this decay time are found for realistic temperature increases and mass changes of the solvent. Similarly, changes in the ground-state solute–solvent potential are found to have only a minimal effect on the ECF decay time. Finally, if the shape of the difference potential is similar for two different observables in a given solvent, the use of the spectral density of one for the description of the (ultrafast) solvent response of the other observable is rationalized.
Response to the “Comment on ‘Heterogeneous two-dimensional nucleation and growth kinetics’ ” [J. Chem. Phys. 107, 10350 (1997)]
Authors: Liu X. Y. , Tsukamoto K.
Published: July 2002

The raised points related to heterogeneous two-dimensional (2-D) nucleation growth model are answered. The function f(m,x) characterizing the height of 2-D heterogeneous nucleation barriers in reference to homogeneous nucleation, has been shown to be different from the 3-D case. The relation between 2-D heterogeneous nucleation and dislocation growth, the condition for “dust-induced kinetic roughening” have been discussed in detail.
The vibrational energy levels in acetylene. III. C212D2
Authors: Herman M. , El Idrissi M. I. , Pisarchik A. , Campargue A. , Gaillot A.-C. , Biennier L. , Di Lonardo G. , Fusina L.
Published: July 2002

We have performed the rovibrational analysis of the absorption spectrum of C212D2 between 5150 and 8000 cm−1, recorded by Fourier transform absorption spectroscopy, and between 12 800 and 16 600 cm−1, recorded by intracavity laser absorption spectroscopy. Respectively 10 and 9 bands are reported for the first time in each range. Improved or new rovibrational parameters were obtained for 34 vibrational levels altogether. The vibrational energies we obtained, together with those reported in the literature, were taken into account to model the vibrational energy pattern in C212D2(X̃ 1Σg+). The analysis was performed in successive steps, inferring each time suitable parameters. The 44/55, 11/33, 12/33, and 1/244 quartic order anharmonic resonances were introduced during the procedure. They altogether define vibrational clusters which are characterized by only two dynamical constants of motion, Ns=V1+V2+V3 and k=l4+l5.
“Spectator” modes in resonance-driven reactions: Three-dimensional quantum calculations of HOCO resonances
Authors: Dzegilenko Fedor N. , Bowman Joel M.
Published: July 2002

We have performed three-degree-of-freedom quantum calculations of HOCO resonances by using a complex potential method. The coordinates we consider are the OH internuclear distance, the CO internuclear distance, and the distance between the centers of mass of the OH and CO fragments. The reduced dimensionality potential has been constructed by adding the nonreactive “spectator” CO coordinate to the previous two-degree-of-freedom potential of Schatz and Dyck [G. C. Schatz and J. Dyck, Chem. Phys. Lett. 188, 11 (1992)] using a Shepard-type interpolation procedure. The positions and lifetimes of more than two hundred resonances are calculated and approximate quantum numbers are assigned. The results are compared with previous two-degree-of-freedom calculations where the CO-stretch mode has not been considered. The appearance of a new group of narrow resonances with a significant CO stretch contribution is reported. The results are tested against the vibrational shifting approximation in which the spectator CO mode is treated adiabatically. The latter is shown to be insufficient for quantitative predictions of resonance positions and widths, however averaged positions and widths are reasonably well described. The rotational shifting approximation is tested by performing the adiabatic rotation calculations of resonances for J=1, K=0 and J=1, K=1 cases, where J is the total angular momentum and K is the body-fixed projection quantum number of a symmetric top. Rotational shifting is shown to work better for K=0 case than for K=1 case.
Comment on “Selection rules for the photoionization of diatomic molecules” [J. Chem. Phys. 93, 3033 (1990)]
Authors: Watson James K. G.
Published: July 2002

In their discussion of the selection rules in the photoionization of diatomic molecules, J. Xie and R. N. Zare [J. Chem. Phys. 93, 3033 (1990)] gave the e/f parity selection rule in the form    (e/f)↔(e/f) for ΔJ−12+l=odd    (e/f)↔(f/e) for ΔJ−12+l=even.   This form is only applicable to molecules with an even number of electrons. It is shown that the general form is    (e/f)↔(e/f) for ΔJ−12(−1)n+l=odd    (e/f)↔(f/e) for ΔJ−12(−1)n+l=even   where n is the number of electrons in the molecule.
On the stochastic approach to the calculation of chemical reaction times and its deterministic limit
Authors: Simons S.
Published: July 2002

A stochastic formulation is developed for the time required for the number of molecules taking part in a chemical reaction to change by a specified amount. With a reaction volume V, asymptotic expressions are obtained for the expectation value of this time and its corresponding standard deviation in the limit of large but finite V. It is shown that as V→∞ these results become equivalent to those obtained by a deterministic approach, and a discussion is given of the regime where stochastic effects become significant.
A simple theory and Monte Carlo simulations for recognition between random heteropolymers and disordered surfaces
Authors: Chakraborty Arup K. , Bratko D.
Published: July 2002

We study the adsorption of random heteropolymers (RHPs) on disordered multifunctional surfaces. Recent replica calculations suggest that when the statistics describing the sequence distribution and the surface site distributions are related in a special way, a first-order adsorption transition occurs in such systems. This phenomenon of recognition between RHPs and disordered surfaces due to statistical pattern matching is studied via Monte Carlo simulations and a simple nonreplica theory. The theory serves to elucidate the simulation results, and suggests that the origin of the first-order adsorption transition is the suppression of loop fluctuations due to competing interactions and the quenched disorder (i.e., frustration).
Cooperative sequential adsorption processes on heterogeneous substrates
Authors: Stacchiola D. J. , Ciacera M. , Zuppa C. , Eggarter T. P. , Zgrablich G.
Published: July 2002

Exact solutions for the cooperative sequential adsorption (CSA) problem on heterogeneous one-dimensional chains is reviewed and extended to the case of dimer adsorption. Then, the much more realistic CSA of dimers on two-dimensional heterogeneous lattices with different site topographies is studied through numerical simulation, and the results are analyzed and interpreted in light of the one-dimensional exact results.
Vibrational relaxation in infrared excited SF6⋅Arn+ cluster ions
Authors: Atrill S. , Stace A. J.
Published: July 2002

An attempt is made to characterize the increase in internal temperature that should accompany the partitioning of a single quantum of vibrational energy within a small SF6⋅Arn+ cluster ion. For each value of n, the kinetic energy release associated with unimolecular (metastable) decay is used to establish an initial temperature for the cluster ion; ∼950 cm−1 of vibrational energy is then deposited into the ν3 vibrational mode of the SF6 moiety (using a CO2 laser). This step promotes additional dissociation which is accompanied by an increase in kinetic energy. From a model due to Klots [J. Chem. Phys. 58, 5364 (1973)] photofragment kinetic energies are predicted on the assumption that energy from the photon is partitioned statistically and leads to an overall increase in the temperature of each ion. Comparisons of experimental and calculated results clearly show that the infrared photoexcitation of SF6 in the ν3 mode leads to incomplete energy randomization. An improved description of the energy relaxation process is provided on the assumption that SF6 undergoes partial vibrational relaxation to either the ν2 or ν4 mode. The energy difference (∼300 cm−1) is then randomized throughout each cluster ion, and is reflected in the magnitude of the measured kinetic energy release accompanying the loss of a single argon atom. The estimated time scale for this process is an order of magnitude faster than the experimentally measured time for the total relaxation of SF6 (ν3=1) in an argon matrix.
Integral-direct coupled cluster calculations of frequency-dependent polarizabilities, transition probabilities and excited-state properties
Authors: Christiansen Ove , Halkier Asger , Koch Henrik , Jo/rgensen Poul , Helgaker Trygve
Published: July 2002

An atomic integral-direct implementation of molecular linear-response properties and excited-state one-electron properties is presented for the coupled cluster models CCS, CC2, and CCSD. Sample calculations are presented for the polarizability of N2 and for excited-state one-electron properties and transition-properties of furan.
Coarsening of random interfaces in the spinodal decomposition of a binary fluid
Authors: Kumaran V.
Published: July 2002

The growth of random interfaces during the late stage spinodal decomposition for a near symmetric quench of a binary fluid is analyzed. Inertial effects are neglected, and the motion of the interface is determined by a balance between the surface tension, which tends to reduce the curvature, and the viscous stresses in the fluid. The interface is described by an “area distribution function” A(K,t), defined so that A(K,t)dKdx is the area of the interface with curvature in the interval dK about K in the volume dx at time t. Here, K=(K12+K22)1/2 is the magnitude of the curvature, and K1 and K2 are the principal curvatures. There is a change in the area distribution function due to a change in the curvature, and due to the tangential compression of the interface. Phenomenological relations for the change in curvature and surface area are obtained using the assumption that the only length scale affecting the dynamics of the interface at a point is the radius of curvature at that point. These relations are inserted in the conservation equation for the interface, and a similarity solution is obtained for the area distribution function. This solution indicates that the area of the interface decreases proportional to t−1 in the late stages of coarsening, and the mean curvature also decreases proportional to t−1. The effect of the motion of the interface on the interfacial concentration profile and interfacial energy is analyzed using a perturbation analysis. The diffusion equation for the concentration in the interfacial region contains an additional source term due to the convective transport of material caused by the motion of the interface, and this causes a correction to the equilibrium concentration profile of the interface. The excess interfacial energy due to the nonequilibrium motion of the interface is calculated using the Cahn–Hilliard square gradient free energy for a near-critical quench. It is found that the variation in the concentration causes an increase in the interfacial energy which is proportional to the curvature K of the interface.
Description of ligand field splitting in terms of density functional theory: Calculations of the split levels of the 2F5/2 and 2F7/2 subterms in CeO and CeF under the weak field coupling scheme
Authors: Dai Dadi , Li Lemin , Ren J. , Whangbo M.-H.
Published: July 2002

A new method of calculating the split levels of the spectroscopic subterms of lanthanide ions under the weak field coupling scheme was formulated based on the density functional theory (DFT) and ligand field theory. To construct the ligand field potential acting on the 4f electrons of a lanthanide compound, the potential of the molecule was obtained by DFT calculations, the 4f-electron contributions to the potential were removed, and the pseudopotentials of the ligands were added to include the Pauli repulsion between the 4f electrons and ligand electrons. The ligand field potential thus obtained includes the effects of the metal-ligand overlap and covalency on ligand-field splitting. This method was tested by calculating the split levels of the 2F5/2 and 2F7/2 subterms associated with the 4f16s1 and 4f16s2 configurations of CeO and CeF, respectively. Our results are in excellent agreement with experiment and indicate that the split levels of lanthanide compounds can be calculated accurately using our method.
Lithium impurity recombination in solid para-hydrogen: A path integral quantum transition state theory study
Authors: Jang Seogjoo , Voth Gregory A.
Published: July 2002

The recombination of two lithium atoms trapped in one-vacancy defect sites of solid para-hydrogen at 4 K and zero external pressure is studied as a quantum activated process. The quantum activation free energy is calculated using path integral quantum transition state theory along with the method of path integral molecular dynamics simulation. The equilibrium volume of the system is determined by a constant pressure method that scales the sides of the rectangular simulation box. At a fixed equilibrium volume of the system, a constraint dynamics path integral simulation is then employed to determine the quantum path centroid free energy barrier along the reaction coordinate, which is taken to be the relative Li–Li separation. The two lithium atoms begin to recombine at a distance of approximately twice the lattice spacing, and the height of the barrier relative to the metastable well is 78±10 K. The rate of the intrinsic recombination step is estimated to be 1.3×103 s−1 at 4 K. It is found that the lithium nuclei exhibit significant tunneling behavior over their classical limit.
Response to “Comment on ‘Modified nonequilibrium molecular dynamics for fluid flows with energy conservation’ ” [J. Chem. Phys. 108, 4351 (1998)]
Authors: Tuckerman Mark E. , Mundy Christopher J. , Balasubramanian Sundaram , Klein Michael L.
Published: July 2002

A new generalized Liouville equation is presented, which correctly incorporates phase space compressibility. A direct consequence of the new Liouville equation is a challenge to the notion that the phase space takes on a fractal character in the nonequilibrium steady state.
Transient solvent dynamics and incoherent control of photodissociation pathways in I2− cluster ions
Authors: Sanov Andrei , Nandi Sreela , Lineberger W. Carl
Published: July 2002

Detailed time-resolved photodissociation and caging dynamics in clusters are studied using I2−(OCS)11 as a model system. We report new observations of product channel-dependent properties of nuclear coherence in the dissociated chromophore, reflecting complex dynamics of the solvent cage. The coherence feature is most pronounced in the caged two-photon channels and its relative amplitude increases with the product size. Shorter delays, on the time scale of coherent I⋯I− motion, favor larger products, allowing for incoherent control of two-photon dissociation pathways by appropriately timing the two laser pulses. As an example of such control, I2−(OCS)2 is produced most effectively by a limited set of pump–probe excitations at short delays. We emphasize generality of these results that relate to caging dynamics in any cluster ions.
Ultracold photoassociative spectroscopy of heteronuclear alkali-metal diatomic molecules
Authors: Wang He , Stwalley William C.
Published: July 2002

We have examined and identified the excited long-range Hund’s case (c) molecular states of the ten heteronuclear alkali metal diatomic molecules which support bound states and can be probed by ultracold photoassociative spectroscopy. Analytical expressions for the heteronuclear long-range free-bound Franck–Condon factors as a function of the internuclear distance R and the vibrational quantum number v are derived and discussed. The KRb system has considerably stronger excited long-range interactions than any other heteronuclear alkali diatomic molecule and has very favorable Franck–Condon factors for the photoassociation process. The heteronuclear photoassociative spectroscopy will provide spectroscopic measurements of the binary elastic scattering lengths of heteronuclear cold collisions which are the crucial parameters for sympathetic cooling of mixed atomic gases.
Orientations and phase transitions in uncrosslinked and crosslinked polymer liquid crystals
Authors: Brostow Witold , Hibner Kazimierz , Walasek Janusz
Published: July 2002

A system of linear polymer liquid crystal (PLC) macromolecules is considered. Each macromolecule constitutes an alternating copolymer of flexible and LC sequences. The macromolecules can be either unconnected or else connected into a PLC network. The system is characterized with respect to local orientation. Competition between energetic effects of anisotropic orienting interactions between LC sequences and entropic effects determined mainly by flexible parts is considered. The Maier and Saupe mean-field approach is assumed for the representation of LC interactions. Types and orders of phase transitions that the system can undergo with respect to local order are discussed in terms of the Landau classification. All transitions are found to be of the first order. Thermodynamical and structural parameters of the system at phase transition points are represented by phase diagrams.
Quantal and semiclassical analysis of vector correlation in molecular photodissociation
Authors: Mo Yuxiang , Suzuki Toshinori
Published: July 2002

General semiclassical expressions for state multipoles and multipole moments have been obtained by the correspondence principle. The expression derived for low-rank multipole moments is identical with that obtained by comparing quantal and classical formulae for one- and two-photon absorption intensity of diatomic molecules [D. A. Case, G. M. McClelland, and D. R. Herschbach, Mol. Phys. 35, 541 (1978)]. For molecular photodissociation, quantal expressions for multipole moments have been obtained by formal expansion of the density matrix by the state multipoles of fragment angular momentum both in the velocity-fixed (VF) and the transition dipole moment fixed (μF) frames. The formulas derived in the two frames were proved to be equivalent. Semiclassical formulas have been also obtained in VF and μF frames by approximating the quantal multipole moments with the semiclassical expressions. The expression thus obtained in the μF frame is in agreement with that reported by Dixon [J. Chem. Phys. 85, 1866 (1986)].
A quenching method in mixed quantum-classical dynamics calculations on nonadiabatic problems
Authors: Wang Lichang
Published: July 2002

A quenching method [Chem. Phys. Lett. 262, 284 (1996)] is extended to study nonadiabatic reactive scattering within a mixed quantum-classical molecular dynamics simulation based on the time dependent self-consistent field. The quenching method is more straightforward for nonadiabatic reactive scattering than for the adiabatic case. A rigorous diabatic-adiabatic transformation for nonadiabatic problems is presented. It provides a theoretical basis for decoupling the bifurcating wavepacket in adiabatic reactive scattering and a new decoupling technique. The derivation illustrates clearly that a diabatic representation is convenient for both adiabatic and nonadiabatic reactive scattering within the mixed quantum-classical formulation. Two model examples are used to demonstrate the advantages of the quenching method for nonadiabatic reactive scattering. A comparison with the full quantum treatment is also made.
Evolution of dissipative processes via a statistical thermodynamic approach. II. Thermodynamic properties of a fluid of bosons
Authors: Madureira Justino R. , Vasconcellos Áurea R. , Luzzi Roberto , Casas-Vázquez José , Jou David
Published: July 2002

On the basis of the generalized Mori–Heisenberg–Langevin equations presented in the preceding paper, we derive and analyze the informational-statistical thermodynamic properties of a fluid of bosons away from equilibrium. We derive the informational entropy and its production, proceeding to an analysis of the several contributions to these state functions arising out of the evolution of dissipative processes in the system.
Collision-induced depolarized scattering by CF4 in a Raman vibrational band
Authors: Bancewicz T. , Elliasmine A. , Godet J.-L. , Le Duff Y.
Published: July 2002

Collision-induced scattering data have been recorded at room temperature for gaseous tetrafluoromethane in a frequency vicinity of the Raman vibrational line ν1=908 cm−1. For the first time, corresponding binary depolarized intensities have been measured in absolute units for frequency shifts up to 110 cm−1 from the band center. Comparison with theoretical semiclassical intensities computed from dipole-induced dipole and dipole-multipole light scattering mechanisms leads to an evaluation of the first derivative of the dipole-quadrupole polarizability tensor A′. This result is in good agreement with recent ab initio quantum-chemistry calculations of the CF4 multipolar polarizabilities.
Out-of-plane vibrations of NH2 in 2-aminopyrimidine and formamide
Authors: McCarthy W. J. , Lapinski L. , Nowak M. J. , Adamowicz L.
Published: July 2002

The out-of-plane vibrations of the amino group in primary amines involve its inversion and rotation relative to the rest of the molecule. These two vibrations in 2-aminopyrimidine (see Fig. 1) were investigated with the combined use of matrix-isolation IR spectroscopy and ab initio quantum mechanical methodology. The ab initio methodology was also applied to another primary amine, formamide, for which a gas-phase IR spectra have been previously assigned. Ab initio potential energy surfaces were calculated in internal coordinates, ω and τ, whose displacements mimicked the inversion and internal rotation normal-mode distortions of the amino group, respectively. Vibrations along these two coordinates were considered uncoupled from all other nuclear motions. Total energy was calculated at the second-order Mo/ller–Plesset perturbation theory level at selected values of ω and τ to allow a least-squares fitting of an analytical function depicting the potential energy curves and surface. A numerical procedure for determining the values of the kinetic energy operator in internal coordinates was also implemented to which an analytical function was fit. Vibrational energy expectation values were variationally determined by utilizing products of Gaussian and sinusoidal functions as the basis set. The resultant calculated fundamental transition energies for the coupled inversion and internal rotation vibrations of 2-aminopyrimidine are vinv=140.6 cm−1 and vrot=440.3 cm−1, respectively. These theoretical values reasonably match the experimental quantities of v≈200 cm−1 and v≈500 cm−1, and allow firm assignment of these two experimental infrared spectral bands to the inversion and internal rotation vibrations of the amino group in 2-aminopyrimidine, respectively. For formamide (see Fig. 2), the calculated transition energies for the inversion and internal rotation vibrations, vinv=249 cm−1 and νrot=602, match the experimental frequencies of ≈289 cm−1 and ≈602 cm−1, and confirm the accuracy of the theoretical method.
Evidence of pure Lb1 fluorescence from redshifted indole-polar solvent complexes in a supersonic jet
Authors: Short Kurt W. , Callis Patrik R.
Published: July 2002

Two-photon polarized fluorescence excitation and vibronically resolved one-photon dispersed fluorescence spectra of the long-wavelength absorbing van der Waals complexes of indole with water, methanol, and formamide were examined for the purpose of firmly assigning the nature of the lowest singlet excited electronic state. The two-photon spectra for all of these complexes have circular/linear polarization ratios of absorptivity (Ω-values) that show that excitation is to the Lb1 state. Analysis of the Franck–Condon (FC) patterns of the dispersed fluorescence for these indole-polar solvent complexes show that emission is also from the Lb1 state in each case. In the emission spectra, the intensity ratios of the origin and ν26 lines are about 2:1, which is the value expected for Lb1 emission. The ν26 vibration is the most intense nonorigin vibronic line, as expected for Lb1 emission. Finally, there is little or no intensity from the ν8, ν9, and ν10 vibrations, which would be strongly active with emission from the La1 state. These results show unequivocally that for these indole-polar solvent complexes the La1 state does not shift in energy below the Lb1 state—contrary to the interpretation of several recent papers. Further support is given to the assignment of Lb1 emission by spectral simulations. The jet-cooled complexes do not exhibit excited state complex (exciplex) characteristics, wherein the solvent is much more strongly bound in the excited state than in the ground state.
A global phase diagram for the ion-dipole model in the mean spherical approximation
Authors: Thiéry R. , Lvov S. N. , Dubessy J.
Published: July 2002

This work is a theoretical study of the phase relations of the ion–dipole mixture, as estimated by the mean spherical approximation. Phase diagrams have been calculated for different values of the model parameters (ion charge, dipole moment, dipole, and ion size) and classified according to the nomenclature of van Konynenburg and Scott. The different types of topologies have been mapped onto a global phase diagram in the space of only two dimensionless parameters, denoted respectively α1 and α2. The α1 parameter measures the ratio of force fields produced by dipoles and ions, whereas the α2 parameter is the ratio of the dipole diameter to the ion diameter. For mixtures of equal-sized ions and dipoles the following sequence of phase topology has been recognized with increasing α1 parameter; type III, type IIIm, type IV, type II, type II with double azeotropy, type IV with double azeotropy, and type III-HA. More complex topologies are obtained for α2 values below and above 1 (gas–gas equilibria, heteroazeotropy, azeotropy). It is shown that the global phase diagram provides insights on the phase topology of water–salt and water–salt–gas systems.
A dielectric theory of spin-lattice relaxation for nuclei with electric quadrupole moments
Authors: Perng Baw-Ching , Ladanyi Branka M.
Published: July 2002

The spin-lattice relaxation time for nuclei possessing electric quadrupole moments is determined mainly by the electric quadrupolar interactions between the nucleus and its environment. Here we give a microscopic formulation of the nuclear quadrupolar relaxation problem for a nucleus of a monatomic solute dissolved in molecular fluids. Our formulation is based on classical statistical mechanics and the interaction site model representation of the intermolecular potential. We assume that the fluctuating field gradient felt by the nucleus is caused mainly by the charge distribution of the surrounding solvent molecules, modulated by the Sternheimer (anti)shielding factor of the nucleus. In the extreme narrowing condition, the problem reduces to the determination of a time integral of the field gradient time correlation function G(t) on the nucleus position. By separation of G(t) into a static contribution G(t=0) and a normalized time correlation function, we seek microscopic expressions for both G(t=0) and its correlation time τQ. Within certain approximations we express τQ in terms of the wavevector-dependent polarization charge correlation time τμ(k), and G(t=0) in terms of the pure solvent charge structure factor Sμ(k) and an analytical function of the solute cavity radius a. Taking as input τμ(k) from molecular dynamics simulations of the pure solvent and Sμ(k) from the extended reference interaction-site model (XRISM) calculation, we apply the theory to the spin lattice relaxation rate of seven quadrupolar nuclei in acetonitrile solution. The solutes considered cover a wide range of size, charge, and nuclear spin quantum number. With reasonable choices of the solute cavity radii, the theory successfully reproduces the experimentally measured 1/T1 for these solutes. Using molecular dynamics simulation, we also investigate the effects on 1/T1 of neglecting the solute mobility. Our simulated data suggest that the solute mobility can reasonably be neglected for spin relaxation of heavy quadrupolar nuclei such as Kr and Xe. Finally, the dielectric continuum limit of our theory is discussed and compared with the related theory developed by Hynes and Wolynes.
Nonlinear elasticity and friction of liquid-crystalline polymer monolayers
Authors: Subbotin A. , ten Brinke G. , Kulichikhin V. G. , Hadziioannou G.
Published: July 2002

In the present paper we consider nonlinear elasticity and friction of grafted persistent chains, which are highly stretched in the normal to the surface direction due to orientational interactions. We examine the normal and the lateral forces both in equilibrium and under shear sliding when the monolayer is confined by a bare surface. We show that in the confined monolayer in equilibrium the tilted orientation of the director becomes stable. In the sliding regime the friction force passes through a maximum value. The additional normal force in the sliding regime, when the distance between the surfaces is fixed, is also considered. We show that this force is attractive for small velocities and becomes repulsive for high velocities after the friction force passes through the maximum value.