bluuebunny/crossref_metadata_2025 huggingface dataset:
A theoretical study of the electron affinity of methylene
Authors: Noro Takeshi , Yoshimine Megumu
Published: July 2002

A b initio multireference configuration interaction calculations yield an electron affinity of 0.604±0.03 eV for methylene (3B1), in excellent agreement with the best observed value of 0.628±0.031 eV. The estimated theoretical error limit of 0.03 eV is based on energy convergence with respect to systematic expansion of both reference configuration space and one-particle basis set. Convergence to the full CI electron affinity is rapid, and significantly accelerated when corrections for quadruple electron excitations are included.
Resonance enhanced electron stimulated desorption
Authors: Gadzuk J. W. , Clark C. W.
Published: July 2002

A theory is presented which accounts for ‘‘giant’’ enhancements in electron stimulated desorption (ESD) yields from adsorbate-covered surfaces if the incident electrons become trapped in a shape or Feshbach resonance associated with the adsorbate. The resulting temporary negative ion is displaced inwards towards the surface as a result of the force provided by the image screening charge. Upon reneutralization, the ‘‘desorbate’’ can be returned high on the dissociative repulsive wall of the neutral-surface potential curve. This process has been modeled within the context of semiclassical Gaussian wave packet dynamics. Recent observations of such giant enhancements in the ESD yields for the system O(a)/Pd(111) are explained in terms of this model, and an atomic physics basis for the resonance in atomic oxygen is proposed.
Intramolecular dynamics of van der Waals molecules: An extended infrared study of ArHF
Authors: Lovejoy Christopher M. , Nesbitt David J.
Published: July 2002

The near-infrared spectrum of ArHF prepared in a slit supersonic expansion is recorded with a difference frequency infrared laser spectrometer. By virtue of the high sensitivity of the technique, and the lack of appreciable spectral congestion at the 10 K jet temperature, we observe 9 of the 11 vibrational states with energies below the Ar+HF(v=1, j=0) dissociation limit. These include (1000), the lowest bound HF (v=1) state, the singly, doubly, and quadruply van der Waals stretch excited states (1001) (1002), and (1004), both the Σ bend (1200) and Π bend (111e,f 0), and the multiply excited, Π bend plus van der Waals stretch (111e,f 1). Two Ar+HF(v=0) states, (0000) and (0001), are also characterized. This spectroscopic information is quite sensitive to the Ar+HF potential energy surface away from the equilibrium configuration, and thus provides a rigorous test of trial potential energy surfaces. Excellent agreement is obtained between experiment and the predictions of a recently reported Ar+HF(v=1) potential.
Chemical equilibrium in argon: Anomaly of density dependence of dimerization reaction in the medium density region
Authors: Kimura Y. , Yoshimura Y. , Nakahara M.
Published: July 2002

We studied the dimerization equilibrium of 2-methyl-2-nitrosopropane in argon at 25.0 °C from about 500 to 1200 kg m−3. It is clarified that in the simplest solvent, argon, there exists a definite difference in the density dependence of the equilibrium constant between the high and medium density regions. In the high density region, the equilibrium constant shows a sizable increase with the solvent density as in the liquid phase. Near the critical density, however, the equilibrium constant shows little density dependence.
Hard spheres: Thermodynamics and geometry
Authors: Reiss Howard , Schaaf Pierre
Published: July 2002

The hard sphere system is discussed with the focus on geometry. Three types of exact relations are derived: (i) purely definitional; (ii) definitional and geometric; and (iii) definitional, geometric, and thermodynamic. This careful separation allows a critical study of the statistical thermodynamics of hard spheres. In particular, a geometric Gibbs equation is derived containing only the fundamental geometric parameters of the system, and a set of exact ‘‘rules’’ can be derived from this equation restricting the behaviors of the fundamental parameters over the entire density range. The geometric Gibbs equation (and the rules) are useful in the derivation of the thermodynamic equation of state, but such application is reserved for a following paper.
Anomalous ultrasonic absorption in alkoxyethanols aqueous solutions near their critical and melting points
Authors: D’Arrigo G. , Paparelli A.
Published: July 2002

Ultrasonic absorption and velocity measurements have been performed in aqueous solutions of ethoxyethanol and n-butoxyethanol in the frequency range of 5–250 MHz and from about 50 °C to the respective melting temperatures (TM). The latter system exhibits a closed loop of miscibility with a LCST at TC=49 °C. The overall behavior of the absorption looks, in general, similar to previously investigated alcohol–water systems and critical binary mixtures. However, it shows two main characteristic features: (a) a noticeable increase of amplitude and dispersion of the peak values as the temperature decreases toward TM; (b) a weak critical anomaly which is seen only at the lowest frequencies and in a narrow temperature interval around TC. A comparison with the frequency and temperature predictions by the Romanov–Solov’ev fluctuation model and by the Ferrell–Bhattacharjee dynamic scaling theory for critical mixtures shows that the observed spectra near TM cannot be explained by critical-like phenomena. The occurrence of pseudocritical fluctuations, which extends their influence from TM to higher temperatures up TC, is suggested.
Rotationally resolved overtone transitions of CHD3 in the visible range
Authors: Ben Kraiem H. , Campargue A. , Chenevier M. , Stoeckel F.
Published: July 2002

Absorption spectra in the 14 900–18 700 cm−1 range have been recorded for gaseous CHD3 at high resolution using the intracavity laser absorption spectroscopy (ICLAS) technique. The observed transitions correspond to the N=6 and 7 overtones of the C–H chromophore. Five bands were identified and rotational constants determined for four of them. The comparison of our experimental data with the calculated band origins and rotational constants obtained by Lewerenz and Quack is discussed. Absolute band intensities are given for seven bands corresponding to the N=5, 6, and 7 polyads.
Microwave spectrum, dipole moment, barrier to internal rotation, and molecular structure of germylazide
Authors: Groner P. , Attia G. M. , Mohamad A. B. , Sullivan J. F. , Li Y. S. , Durig J. R.
Published: July 2002

The microwave spectra of three isotopic Ge species of germyl azide, GeH3N3, have been assigned. The splittings due to internal rotation of the germyl group have been analyzed yielding a threefold barrier of 86.6(1) cm−1. An electric dipole moment of 2.58(2) D has been determined from the Stark effect. The following refined structural parameters have been obtained with a fixed and slightly bent azide group: r(GeN)=1.866(12) Å, r(GeH)=1.497(8) Å, α(GeNN)=115.9(14)°, α(HGeH)=112.2(10)° and a tilt of the symmetric germyl group of 4.0° away from the azide group.
Calculation of vibrational transition probabilities in molecular collisions: A recursive algebraic procedure
Authors: Echave Julián , Fernández Francisco M. , Castro Eduardo A. , Micha David A.
Published: July 2002

The vibrational energy transfer in collinear collisions between diatomic molecules is studied by means of a recursive algebraic approach applicable to several degrees of freedom. Introducing classical relative trajectories the problem is reduced to solving the Schrödinger equation with a time-dependent bilinear Hamiltonian. On using the equations of motion for the creation and annihilation operators, simple recurrence relations for the transition amplitudes are obtained. Transition probabilities between several vibrational states are calculated for N2+O2 to illustrate the advantages of the computational approach for high vibrational quantum numbers.
Vibrational state dependence of ionic rotational branching ratios in resonance enhanced multiphoton ionization of CH
Authors: Rudolph H. , Stephens J. A. , McKoy V. , Lee M.-T.
Published: July 2002

We show that rapid evolution of a Rydberg orbital with internuclear distance in a resonance enhanced multiphoton ionization (REMPI) process can have a profound influence on the production of molecular ions in alternative rotational states. This is illustrated by calculations of ionic rotational branching ratios for (2+1′) REMPI via the O11 (20.5) branch of the E′ 2Σ+(3pσ) Rydberg state of CH. The rotational propensity rule for ionization changes from ΔN=odd (ΔN=N+−Ni) at lower vibrational excitation, as expected from the ΔN+l=odd selection rule, to ΔN=even at higher vibrational levels. This effect is expected to be quite general and should be most readily observable in diatomic hydrides.
Time-resolved electron energy loss spectroscopy study of water desorption from Ag(011)
Authors: Wu K. J. , Peterson L. D. , Elliott G. S. , Kevan S. D.
Published: July 2002

We present time-resolved electron energy loss spectroscopy (EELS) results for the desorption of submonolayer coverages of H2O and D2O from Ag(011). The measurements were performed isothermally and effectively at constant coverage. At coverages above a few percent of a monolayer, we observe that the desorption is characterized by zero-order kinetics. That is, the desorption rate is independent of coverage. We hypothesize that this results from the formation of two-dimensional water islands on the surface at all coverages and temperatures measured. The desorption process is governed in part by the dissociation of water from the edges of these islands. Rapid diffusion on the surface maintains a quasiequilibrium between the molecules bound to islands and isolated adsorbed water molecules, thereby leading to pseudo-zero-order kinetics. This result is interpreted upon general thermodynamic grounds, and also using a simple kinetic model which leads to pseudo-zero-order desorption kinetics. An unusual hydrogen kinetic isotope effect is reported which lends support to our interpretation.
Observation of direct and collision-induced double resonance of a molecular ion
Authors: Pursell C. J. , Weliky D. P. , Ho W. C. , Takagi K. , Oka T.
Published: July 2002

The double resonance technique has been applied to a molecular ion. We have observed microwave-infrared double resonance signals of HN+2 produced in a hollow cathode discharge at low pressures (20–200 mTorr). A color center laser with 2–20 mWatts of power provided the infrared signal radiation, and a millimeter wave klystron with ∼400 mWatts of power provided the microwave pump radiation. The frequency of the microwave radiation was swept and the double resonance signal was detected through variation of the infrared power. Using the R(1) and P(1)infrared transitions we have observed the J=1←0 rotational transition in both the ground state and the ν1 state. We have observed not only the direct three-level double resonance signals, but also collision-induced four-level double resonance signals indicating the existence of some selection rules for the Langevin potential dominated ion–neutral interaction. The major results of this paper are: (1) The double resonance method is now applicable to molecular ions and (2) ion–molecule collisions have selection rules.
Theoretical study of anharmonicity in the vibrational spectrum of the perfluorocyclopropenyl cation
Authors: Xie Yaoming , Boggs James E.
Published: July 2002

Complete theoretical calculations for the structure, anharmonic force field up to partial sixth order, and anharmonic vibrational frequencies of C3F+3 have been carried out. The procedure included ab initio calculation of the vibrational potential-energy surface at the 6-311G plus double polarization plus local MP4(SDQ) level, followed by a complete, 12-mode variational solution of the vibrational Schrödinger equation using a configuration-interaction (CI) expansion from a large, well-selected harmonic oscillator basis. The geometric parameters of C3F+3 (D3h) were optimized as 1.3796 Å for the CC bond lengths and 1.2615 Å for the CF distances. Localized orbitals show strong π-bond character for the CF linkages, conjugated with the ring π orbital. The fundamental vibrational frequencies of C3F+3 are 1999.5, 742.8 (a′1); 767.3 (a2); 1596.9, 998.9, 271.3 (e′); 250.0 (a″2); and 664.1 (e″). These frequencies agree with condensed phase measurements of Raman and infrared spectra with a ±11.5 cm−1 average deviation, the largest difference appearing for the CF bending and wagging frequencies. The first vibrational overtone frequencies of C3F+3 are also predicted. This completely ab initio calculation of anharmonic frequencies also leads to detailed bond characterization and full information on all intermode interactions.
Probing the O(1D)+CO2 reaction with second-derivative modulated diode laser spectroscopy
Authors: Sedlacek Arthur J. , Harding David R. , Weston Ralph E. , Kreutz Thomas G. , Flynn George W.
Published: July 2002

The reaction of electronically excited O(1D) atoms with CO2 to form CO+O2(1Σ+g,1Δg,3Σ−g) has been probed with second-derivative modulated diode laser spectroscopy. The O(1D) atoms were generated by the pulsed 193 nm laser photolysis of N2O, and the reaction was followed by monitoring the formation of CO as a function of the number of laser pulses. These experiments have revealed that the quantum yield for this reaction is (2.1±0.3)×10−3 molecules/photon absorbed. The very low quantum efficiency suggests that a significant potential barrier exists on the reaction coordinate which prevents the vast majority of collisions from fragmenting into products distinguishable from reactants. The rate constant, measured indirectly by comparison with the rate constant for quenching, is found to be (2.4±0.5)×10−13 cm3 molecule−1 s−1 and represents the best estimate currently available in the literature for the reaction rate constant. In experiments involving 16O(1D)+12C18O2, the resulting product, 12C18O, indicates that no isotopic exchange takes place in the reaction. Comparison with deactivation results suggests that the reaction proceeds by a simple, direct oxygen-atom abstraction with a potential barrier, whereas the quenching channel involves a long-lived intermediate.
Importance of high-order interactions in models of molecular solids at high pressure
Authors: Raynor S.
Published: July 2002

An application of the ab initio subcell approach to solid H2 is used to determine the importance of high-order interactions on the calculated interaction energy in molecular solids at high pressures. The errors incurred using clusters (up to a 209-membered cluster) or anisotropic N-body potentials as representations of the solid at 3, 1, 0.5 and 0.1 Mbar are reported. For the cluster calculations, large errors at all pressures are obtained, even for the largest clusters studied ∼50% error for 13-membered clusters, decreasing to ∼20% for 209-membered clusters). However, errors even more severe occur using N-body potentials. All N-body potentials, up to and including ten-body potentials, were calculated for the solid. Large oscillations in error were observed as higher N-body terms were added, with errors remaining above 10% until at least ten-, eight-, six- or three-body interactions were added for the 3, 1, 0.5 and 0.1 Mbar calculations, respectively. At the highest pressures, addition of three-body terms caused an increase in the magnitude of the error over that obtained from two-body terms alone. Use of cluster or N-body approaches to model high pressure solids is therefore not recommended.
A stochastic approach to vibrational relaxation of a diatomic near dissociation
Authors: Sceats M. G.
Published: July 2002

A stochastic model employing the frequency dependent friction of separated atoms in a fluid of arbitrary density is used to evaluate the vibrational relaxation rate of a diatomic near dissociation. The utility of the approach is demonstrated by comparison with molecular dynamics simulations of Nordholm et al. [Chem. Phys. 23, 135 (1977)] for Br2 in fluid argon at 300 K, and atom–diatom trajectories of Koshi et al. [J. Chem. Phys. 82, 4903 (1985)] at 2000 and 3000 K. The model shows that binary-collision weak-coupling theory is adequate to quantitatively explain the results obtained for dense fluids, and shows that the energy dependence of 〈ΔE〉 exhibits a maximum near dissociation as a result of the tradeoff of a decreasing oscillator kinetic energy available for transfer and an increasing transfer probability arising from the changing adiabatic character of the collisions. Rotational effects are unimportant.
Statistical dynamics and kinetics of unimolecular processes
Authors: Dumont Randall S.
Published: July 2002

The statistical theory of arbitrary unimolecular reactions is developed with an ergodic theoretic basis. In the process, unimolecular kinetics is derived from dynamics, in terms of well-defined mixing and time-scale assumptions. The statistical theory is then taken beyond kinetics via the new ‘‘generalized flux renewal model’’ which incorporates ‘‘nonstatistical effects’’ due to nonzero relaxation time and direct components. Effects of direct component delays and nonzero relaxation times are examined closely. In particular, an estimate of the longest reaction time scale accounting for these effects is provided.
Vacuum ultraviolet spectroscopy of the Cl2 molecule trapped in pure neon, pure argon, or mixed neon–argon matrices
Authors: Gürtler P. , Kunz H. , Le Calvé J.
Published: July 2002

Synchrotron radiation excitation and emission spectra with lifetime measurements are reported for the first time in the VUV region for systems consisting of Cl2 molecules trapped in a neon matrix, an argon matrix, and mixed Ar/Ne matrices. In pure neon, the emission spectrum of the D′→A′ ‘‘laser’’ transition at 4.7 eV of the Cl2 molecule is vibrationally well resolved and constitutes an interesting example of UV spectroscopy of a matrix ‘‘isolated’’ molecule. In pure argon or mixed Ar/Ne matrices, new broad emissions at 4.1, 3.8, and 3.5 eV are clearly identified, which result from the specific interaction between Cl*2 and Ar and are attributed to different charge–transfer states of the ArCl+Cl− entity. The Ar concentration dependence and the time-gated spectra are shown to be especially useful in interpreting the large differences observed between the pure neon and the pure argon matrix case.
Temperature dependence of reactions of N+4 and N+3 with O2 in the range 552–64 K
Authors: Hiraoka Kenzo
Published: July 2002

The rate constants for the reactions of N+4 and N+3 with O2 in a few Torr of nitrogen have been studied in the temperature range of 552–64 K with a pulsed electron-beam high-pressure mass spectrometer. A steep increase of the rate constants for both reactions are observed below ∼160 K. This is due to the participation of higher clusters N+4(N2)n and N+3(N2)n in the reactions. The ratio of the product yield of NO+2 and NO+ from the reaction N+3 +O2 was also measured as a function of temperature. It increases with a decrease in temperature from 0 at 552 K to 7.5 at 64 K.
Laser vaporization generation of 69Ga31P+ and 71Ga31P+ for neon matrix electron spin resonance studies: Electronic structure comparison with GaAs+
Authors: Knight Lon. B. , Herlong John O.
Published: July 2002

The 69GaP+ and 71GaP+ molecular ions have been generated by the combined methods of photoionization/laser vaporization for trapping in neon matrices at 4 K for electron spin resonance (ESR) investigation. The ground electronic state of GaP+ has been determined as X 4∑ and its electronic structure based on nuclear hyperfine properties is compared with the isovalent ion, GaAs+. The magnetic parameters (MHz) for Ga31P+ are: g⊥ =1.9836(5); A⊥ (69Ga)=188.6(1); A⊥ (71Ga)=239.4(1); A∥ (69Ga)=260(30); A∥ (71Ga)=300(10); A⊥ (31P)=108.0(1); and A∥ (31P)≊200(150). The g and A values observed for 31P(4S1/2) atoms in these neon matrices show closer agreement with the gas phase parameters compared to previous values reported for the heavier rare gases.
Spin relaxation of I>1 nuclei in anisotropic systems. II. Inversion recovery and even-rank polarization decay
Authors: Furó István , Halle Bertil
Published: July 2002

The response of half-integral spin I>1 nuclei in anisotropic systems to pulse sequences that probe longitudinal quadrupolar relaxation is investigated. The dynamical coupling among polarizations of different rank renders the response more complicated than in the case of I=1 nuclei. Nevertheless, for I=3/2 and I=5/2 nuclei, exponential or biexponential spectral decays can be produced that enable accurate determination of the motional spectral densities j1 and j2. While the inversion recovery experiment, which probes the evolution of the odd-rank polarizations, is useful mainly for I=3/2, the decay of the even-rank polarizations is conveniently analyzed also for I=5/2. We thus describe pulse sequences, analogous to the Jeener–Broekaert sequence for I=1, that yield exponential decay for I=3/2 and biexponential (sum or difference) decay for I=5/2.
The yield of metastable atoms through dissociative recombination of O+2 ions with electrons
Authors: Queffelec J. L. , Rowe B. R. , Vallée F. , Gomet J. C. , Morlais M.
Published: July 2002

The yield of metastable oxygen atoms through dissociative recombination of O+2 ions with electrons has been studied using a plasma flow tube experiment. For O+2 with high vibrational excitation (around v=9) it was found that half of the oxygen atoms are formed on the O(1D) state and that the branching ratio toward O(1S) is large (∼0.4). Using Xe+ instead of Ar+ as precursor ions, it was shown that the O(1S) yield is much less for ions with low vibrational excitation. However, the present experimental results are not compatible with the extremely low theoretical value of this yield which was reported recently for O+2 (v=0).
Further theoretical studies on B2H4 and B2H+4
Authors: Curtiss Larry A. , Pople John A.
Published: July 2002

The vertical ionization potentials of the D2d and C2v structures of B2H4 are reported at the G1 level of ab initio molecular orbital theory. The results support the interpretation by Ruscić, Schwarz, and Berkowitz of their new photoionization experiment in terms of a C2v bridged structure of B2H4. In addition, the bridged C2v B2H+4 cation is found to have a very small barrier to inversion (1 kcal/mol).
Density effects on high-n molecular Rydberg states: CH3I and C6H6 in H2 and Ar
Authors: Asaf U. , Felps W. S. , Rupnik K. , McGlynn S. P. , Ascarelli G.
Published: July 2002

The absorption spectra of high-n Rydberg states of methyl iodide and benzene perturbed by varying number densities of hydrogen or argon, range 0.9×1020–10.5×1020 cm−3 for H2 and 0.6×1020–7.5×1020 cm−3 for Ar, have been investigated. The high-n molecular states of both absorbers were found to shift linearly with the number density of atomic Ar and molecular H2 scatterers. The Fermi formula modified by the Alekseev–Sobel’man polarization term provides an excellent fit of the shift data. The electron scattering lengths obtained are: 0.93 a0 for H2 and −1.63 a0 for Ar using the CH3I absorber; and 0.99 a0 for H2 and −1.57 a0 for Ar using the C6H6 absorber. The electron scattering lengths for H2 and Ar agree with the results of an empirical model that correlates scattering lengths and the polarizabilities α(spherical) for inert atoms and α2(nonspherical) for H2 molecule.
Dynamics of charge transfer from molecule to semiconductor at surface: Numerical method for nonadiabaticity and irreversibility in discrete-continuum transition
Authors: Suzuki Masato , Nasu Keiichiro
Published: July 2002

The transition probability of an electron from a molecule to a conduction band at an insulator surface is investigated by using the Fano–Anderson model, so as to clarify the effects of nonadiabaticity and irreversibility on this process. The potential for the center-of-mass motion of the molecule near the surface is assumed to be harmonic and this motion is solved numerically by using the real time Trotter’s formula, without assuming any a priori trajectories. The transition probability is calculated as a function of the basic three parameters: the conduction band width (≡W), the incident energy of the molecule (≡Ekin), and the resonance transfer integral of electron between the molecule and atoms at the surface (≡Tint). When W is small, the probability is shown to increase as it increases, since W results in the depopulation and the dephasing of surface atomic levels and suppresses the back-electron transfer. On the other hand, in the case of large W, the transition probability decreases with its increase, since the density of states of the band itself decreases. Thus, the probability is found to become maximum in the intermediate case of W. This probability is also calculated as a function of Ekin and Tint. These results are compared with the Landau–Zener formula for the multilevel crossing, in connection with recent experiments.
The multiconfiguration time-dependent Hartree–Fock method based on a closed-shell-type multiconfiguration self−consistent field reference state and its application to the LiH molecule
Authors: Sasagane Kotoku , Mori Kazuhide , Ichihara Akira , Itoh Reikichi
Published: July 2002

The linear response calculations in the multiconfiguration time-dependent Hartree–Fock (MCTDHF) approximation with a closed-shell-type MCSCF state as the time-independent reference state are discussed. The application to the LiH molecule with a small basis set ([4s2p1d/2s1p]) shows validity of our MCTDHF approach to the singlet ground state. Our MCSCF correlation energy is 97% of the total (=full CI) correlation energy and the MCTDHF excitation energies are in good agreements with the Δ full CI excitation energies. The Born–Oppenheimer potential energy curves for the lowest three singlet states of LiH and the corresponding vibrational level spacings, the transition moments, the oscillator strengths, and the frequency-dependent dipole polarizabilities are reported. All of these results imply the potentiality of our MCTDHF method for the future work with the larger basis set. One of such basis sets ([9s8p4d/8s7p1d]) is referentially used only at the single-configuration TDHF level, and the resultant near-Hartree–Fock polarizability and Thomas–Reiche–Kuhn sum rule is very promising.
Spectroscopy and dynamics of the highly excited nonrotating three-dimensional H+3 molecular ion
Authors: Brass Otto , Tennyson Jonathan , Pollak Eli
Published: July 2002

A study of the bound states of the H+3 molecular ion at zero total angular momentum is presented. Wave functions are shown for the accurate ab initio Meyer–Botschwina–Burton potential energy surface and the more approximate diatomics in molecules (DIM) surface. The qualitative behavior is similar for the two potentials. The analytic form of the DIM surface enables a study that reaches energies as high as the dissociation threshold. Quantum states are found to localize regularly around the horseshoe periodic orbits found in previous classical studies. There is good agreement between a semiclassical periodic orbit quantization formula and the exact quantum energies. The antisymmetric stretch frequency with respect to the orbit is estimated classically and quantum mechanically and found to be in agreement with a previous estimate. A three-dimensional stability analysis of the horseshoe orbit is presented and used as a basis for the semiclassical theory. The implications on the assignment of the coarse grained photodissociation spectrum measured by Carrington and Kennedy are discussed.
Theory and experiments on the effects of perturbations on nonlinear chemical systems: Generation of multiple attractors and efficiency
Authors: Hjelmfelt Allen , Harding Robert H. , Tsujimoto Kim K. , Ross John
Published: July 2002

Periodic perturbations are applied to the input fluxes of reactants in a system which exhibits autonomous oscillations, the combustion of acetaldehyde (ACH) and oxygen, and a system which exhibits damped oscillations, the combustion of methane and oxygen. The ACH system is studied by experiments and numerical analysis and the methane system is studied by numerical analysis. The periodic perturbations are in the form of a two-term Fourier series. Such perturbations may generate multiple attractors, which are either periodic or chaotic. We discuss two types of bistable responses: a new phase bistability, in which a subharmonic frequency is added to a sinusoidal perturbation at different phases relative to the periodic response; and jump phenomena, in which the resonant frequency of a nonlinear oscillator depends on the amplitude of the periodic perturbation. Both the ACH and the methane systems confirm the phase bistability. The additional complex behavior of bistability due to jump phenomena is seen only in calculations in the methane system. In both types of bistability a hysteresis loop is formed as we vary the form of the periodic perturbation. In the methane system, we find period doubling to chaos occuring on one branch of the hysteresis loop while the other branch remains periodic. The methane system has been studied in the context of the efficiency of power production. We calculate the efficiency corresponding to each bistable attractor and find one branch of each pair to be the more efficient mode of operation. In the case of the coexisting periodic and chaotic attractors the chaotic attractor is the more efficient mode of operation.
Resonant third-order nonlinear optical properties of poly(3-dodecylthiophene)
Authors: Singh Bhanu P. , Samoc Marek , Nalwa Hari S. , Prasad Paras N.
Published: July 2002

We have investigated the resonant nonlinear optical properties of both chemically prepared and electrochemically prepared poly(3-dodecylthiophene) samples using femtosecond degenerate four-wave mixing. The measured χ(3) values for the two polymers are 3×10−10 and 5×10−10 esu at 602 nm. The value of χ(3) at 705 nm is an order of magnitude less. The nonlinearity shows a subpicosecond response. The power dependence of the conjugate reflectivity shows saturation at high input powers. The origin of this saturation is discussed in terms of the saturable absorber behavior. It is concluded that the saturation is consistent with the predictions of simple kinetic models. The origin of the phase conjugate response is discussed in terms of two models: (i) phase space filling model involving unrelaxed excitons and (ii) rapid conformational deformation leading to shift of oscillator strength to photogenerated polaronic states. The analysis of our results favors the mechanism involving unrelaxed excitons as the source of the observed third-order optical nonlinearity.
The spontaneous resonance Raman scattering of CH3I in a supersonic jet
Authors: Wang P. G. , Zhang Y. P. , Ruggles C. J. , Ziegler L. D.
Published: July 2002

The resonance Raman scattering of methyl iodide cooled in neat and seeded supersonic jets has been observed. The incident radiation is resonant with the X→B Rydberg transition (∼200 nm). To our knowledge this is the first reported observation of the resonance Raman scattering of jet-cooled species. Depolarization ratio measurements determine the rotational temperature of the molecular beam to be 10 K (4% CH3I/2 atm He). The only observed spectral evidence of (CH3I)n species (n≥2) in the cooled molecular beam is the appearance of the resonance Raman spectra of I2 produced by the photodecomposition of methyl iodide clusters. The nascent I2 is born with an extremely hot (∼1000 K) vibrational distribution. The excitation profile of the I2 vibrational resonance Raman scattering reveals that the absorption band of the clusters are much broader than that of the monomer. Semiempirical calculations (AM1) predict a CH3I dimer with a bent ‘‘heat-to-head’’ ground-state equilibrium structure which is a favorable orientation for the production of I2.
Observation of the formation of N+ and ArN+ in the collisions of Ar+(2P3/2,1/2) with N2
Authors: Flesch G. D. , Ng C. Y.
Published: July 2002

Absolute total cross sections for the reactions, Ar+(2P3/2,1/2)+N2→N++N+Ar [reaction (1)] and ArN++N [reaction (2)], have been measured in the center-of-mass collision energy (Ec.m.) range of 6.2–123.5 eV. The appearance energy for the formation of N+ (Ec.m.=8.65±0.21 eV) is in agreement with the thermochemical threshold for reaction (1). The comparison of the collision energy dependence of the N+ cross section with the photoionization efficiency spectrum of N+ from N2 suggests that the predissociative multielectron states of N+2, C̃ 2Σ+u, F̃ 2Σ+g, G̃ 2Σ+g, and 2Σ+g (2σg)−1, which are responsible for the dissociative photoionization of N2, also play a role in the formation of N+ via reaction (1). Product ArN+ ions of reaction (2) are only observed in the Ec.m. range of 8.2–41.2 eV. At Ec.m. slightly above the thermochemical thresholds of reactions (1) and (2), the majority of ArN+ and N+ ions are scattered backward and forward with respect to the center-of-mass velocity of reactant Ar+, respectively. This observation is rationalized by a charge transfer predissociation mechanism which involves the formation of ArN+ and N+ ions via nearly collinear Ar+-N-N collision configurations at Ec.m. near the thresholds of reactions (1) and (2). At Ec.m.≥11 eV, more than 92% of the charge transfer product N+2 ions are found to be slow ions formed mostly by the long-range electron jump mechanism.
Electron scattering in dense atomic and molecular gases: An empirical correlation of polarizability and electron scattering length
Authors: Rupnik K. , Asaf U. , McGlynn S. P.
Published: July 2002

A linear correlation exists between the electron scattering length, as measured by a pressure shift method, and the polarizabilities for He, Ne, Ar, Kr, and Xe gases. The correlative algorithm has excellent predictive capability for the electron scattering lengths of mixtures of rare gases, simple molecular gases such as H2 and N2 and even complex molecular entities such as methane, CH4.
Rate constants for reactions of NO− with N2O, 14N15NO, and 15NO2
Authors: Morris Robert A. , Viggiano A. A. , Paulson John F.
Published: July 2002

The gas phase kinetics of the reactions of NO− with N2O and 14N15NO have been investigated at 143 and 298 K. The reaction of NO− with 15NO2 was studied at 298 K. For the reaction of NO− with N2O, production of N2O− and NO−2 is very slow with rate constants on the order of 10−14 cm3s−1. Isotope exchange of NO− with 14N15NO is slow with rate constant values near 10−11 cm3 s−1. The reaction of NO− with 15NO2 is rapid (k=5.1×10−10 cm3 s−1) and proceeds by electron transfer with no measurable O atom transfer.
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o study of multiphoton absorption properties of formaldehyde, acetaldehyde, and acetone
Authors: Galasso V.
Published: July 2002

The low-lying Rydberg and intravalence excited states of formaldehyde, acetaldehyde, and acetone, accessed by multiphoton absorption, have been investigated at ab initio level according to quantum electrodynamical formalisms, by utilizing random-phase-approximation vertical transition energies and amplitudes. For all three carbonyls, two-photon spectroscopic properties which could be detected with various experimental arrangements have been reported. For formaldehyde, an exhaustive overview on spectroscopic observables associated with multiphoton absorption is presented. The transition probability coefficients and polarization ratios for two-, three-, and four-photon single-color absorption from plane polarized, circularly polarized, and unpolarized light have been evaluated. The molecular response to concerted absorption of two and three photons from two laser beams under various polarization conditions has been investigated as a function of the photon energies. An attempt has also been made to estimate the magnitude and direction of the electrochromic changes in two-photon spectroscopic properties brought about by an external static electric field.
Does squaring the quantum Monte Carlo weights give the exact quantum probability distribution?
Authors: Reynolds Peter J.
Published: July 2002

It is shown that the recently-proposed method of East et al. [J. Chem. Phys. 89, 4880 (1988)] for stochastically obtaining the exact quantum mechanical probability distribution ‖φ‖2 is in error. The Green’s function generator for the proposed process results in a Schrödinger-like equation for which ‖φ‖2 is not a solution. We carefully follow the logic of East et al. to discover their error.
Fourier transform emission spectroscopy of the jet-cooled CCN free radical
Authors: Oliphant N. , Lee A. , Bernath P. F. , Brazier C. R.
Published: July 2002

The Ã 2Δ–X̃ 2Π electronic transition of the CCN free radical was observed in emission with a high-resolution Fourier transform spectrometer. The CCN was jet-cooled in a corona-excited supersonic jet expansion of diazoacetonitrile (HC(N2)CN) in helium. From the 000–000, 000–001, 000–002, and 000–100 vibronic bands spectroscopic constants were derived including the ground-state vibrational frequencies, ν3=1050.7636(6), 2ν3=2094.8157(18), and ν1=1923.2547(69) cm−1.
Formation of high mass carbon cluster ions from laser ablation of polymers and thin carbon films
Authors: Creasy William R. , Brenna J. T.
Published: July 2002

Three materials were studied by laser ablation/Fourier transform mass spectrometry, using 266 nm laser radiation: a copolymer of ethylene and tetrafluoroethylene (ETFE), polyphenylene sulfide (PPS), and a diamond-like carbon film (DLC). In each case, positive ion mass spectra exhibit primarily even-numbered, high mass carbon clusters (‘‘fullerenes’’) of the type previously reported for graphite ablation. In the case of ETFE, a large C+60 peak (‘‘buckminsterfullerene’’) was observed. The polymer spectra showed a strong dependence on the number of laser pulses on one spot and the laser power density. For ETFE, the fullerene ion relative intensity first increases and then decreases as a function of the number of laser pulses. For the DLC film, fullerenes are observed with a single laser pulse on a fresh spot of the sample. The results are interpreted in terms of a gas phase growth model for the fullerene ion formation.
Rovibrational excitation of carbon monoxide by energy transfer from metastable nitrogen
Authors: Fraser Mark E. , Rawlins Wilson T. , Miller Steven M.
Published: July 2002

The CO fundamental vibration–rotation spectra resulting from the interaction of discharged nitrogen with carbon monoxide at low pressure (∼3 mTorr) exhibit bimodal rotational distributions. We have identified 14 vibrational levels of a rotationally relaxed (80 K) component and eight vibrational levels from a rotationally excited component. The eight rotationally excited bands are best reproduced by a statistical distribution E=ER+EV=3.7 eV, which provides sufficient population in the region of the Fortrat reversal (J∼90) to account for the observed R-branch bandhead formation. The rotationally relaxed vibrational levels are populated by single- and two-quantum transfer from N2(v), N2(v)+CO→N2(v−1,2)+CO(v=1,2), and radiative cascade from CO(A) produced by quenching of N2(a′), N2(a′ 1Σ−u) +CO→N2(X,v)+CO(A 1Π)→CO(v≤9)+hν, and relaxation of the rotationally excited component. Kinetic and energetic arguments indicate that a branch of N2(a′) quenching N2(a′ 1Σ−u) +CO→N2(X,v)+CO(v≤14,J) is responsible for the rotationally excited component. Surprisal analysis indicates two dynamic mechanisms are responsible for the rotationally excited component. We have modeled the vibrational distribution of the rotationally excited component with equal contributions from a statistical (all v) process and a process favoring excitation of low vibrational levels (v≤4).
Reactions of intermetallic clusters
Authors: Farley R. W. , Castleman A. W.
Published: July 2002

Reaction of bismuth–alkali clusters with closed-shell HX acids provides insight into the structures, formation, and stabilities of these intermetallic species. HC1 and HI are observed to quantitatively strip BixNay and BixKy, respectively, of their alkali component, leaving bare bismuth clusters as the only bismuth-containing species detected. Product bismuth clusters exhibit the same distribution observed when pure bismuth is evaporated in the source. Though evaporated simultaneously from the same crucible, this suggests alkali atoms condense onto existing bismuth clusters and have negligible effect on their formation and consequent distribution. The indistinguishibility of reacted and pure bismuth cluster distributions further argues against the simple replacement of alkali atoms with hydrogen in these reactions. This is considered further evidence that the alkali atoms are external to the stable bismuth Zintl anionic structures. Reactivities of BixNay clusters with HC1 are estimated to lie between 3×10−13 for Bi4Na, to greater than 4×10−11 for clusters possessing large numbers of alkali atoms. Bare bismuth clusters are observed in separate experiments to react significantly more slowly with rates of 1–9×10−14 and exhibit little variation of reactivity with size. The bismuth clusters may thus be considered a relatively inert substrate upon which the alkali overlayer reacts.
Crossed-beam study of the reaction of van der Waals molecule H+(NO)2
Authors: Honma Kenji , Kajimoto Okitsugu
Published: July 2002

Chemiluminescent reaction H+(NO)2 →HNO*+NO was studied under single collision condition. The built-in third body much enhanced the formation of HNO*(A 1A″) in bimolecular relatively large population in bending vibration (ν3 ) as compared with the HNO* produced from the termolecular recombination, H+NO+M. This apparent excitation in bending mode can be attributed to the smaller internal energy of HNO* produced in H+(NO)2 reaction. Higher rotational states of the (001) vibration, if formed in H+NO+M reaction, most probably suffer rapid losses to X 1A′ state by internal conversion. The lower energy content of HNO* formed in H+(NO)2 reaction suppresses this internal conversion and hence the relative population of the (001) state becomes large. The reaction probability was also measured as a function of collision energy and the result indicates the absence of the reaction barrier.
Initial cross section for photodissociation of phosgene on Ag(111)
Authors: Zhou X.-L. , White J. M.
Published: July 2002

The initial cross section for UV photodissociation of phosgene (Cl2CO) on Ag(111) at 100 K has been measured. With photon energies greater than 2.6 eV, submonolayer Cl2CO is readily photodissociated to surface Cl(a) and gas phase CO(g). The evolution of CO during photodissociation is readily monitored and used to calculate the initial photodissociation rate and cross section. The cross section is higher than the gas phase absorption cross section and is in the range of 10−18–10−19 cm2. It depends on the wavelength and the Cl2CO coverage.
Observation of a SO+2 threshold photoelectron band in the energy range 14.4–15.5 eV
Authors: Norwood K. , Ng C. Y.
Published: July 2002

In orderto gain insight into the autoionization mechanisms of sulfur dioxide, the threshold photoelectron spectrum was measured in the wavelength region of 800−860 Angtroms.(AIP)
Raman spectroscopic study of vibrational and rotational relaxations of CO2−3 ion in molten Li2CO3
Authors: Matsumoto Morihiko , Okazaki Susumu , Okada Isao
Published: July 2002

Polarized and depolarized Raman scattering spectra for the ν1 (A′i) mode of the CO2−3 ion in the molten Li2 CO3 system at 1023 K have been measured. The interference from background radiation could be eliminated by a phase detection method. Rotational and vibrational autocorrelation functions were obtained by Fourier transformation of the spectra. The rate of the rotational relaxation of the CO2−3 ion in molten Li2 CO3 at 1023 K is considerably slower than that of the NO−3 ion in molten LiNO3 at 623 K, whereas the vibrational relaxation of the former is quicker than that of the latter.
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o Hartree–Fock perturbed-cluster treatment of local defects in crystals
Authors: Pisani C. , Dovesi R. , Nada R. , Kantorovich L. N.
Published: July 2002

An ab initio Hartree–Fock self-consistent-field embedding scheme is presented for the treatment of local defects in crystals. It is a ‘‘perturbed-cluster’’ (PC) scheme in the sense that the density matrix in the defect region is obtained by taking as a reference the solution for a molecular cluster that describes that region. Corrective terms are then added in order to realize the coupling between the cluster and the surrounding medium, which are expressed in terms of the density of states of the perfect host crystal. The approximations adopted are much less severe than in previous formulations; essentially, it is assumed that the density of states projected onto the indented crystal surrounding the defect region is only marginally affected by the presence of the defect. New PC equations are derived and their features are discussed with reference to previous formulations. The algorithms needed to implement the new theory and to calculate the defect formation energy are described in some detail. The main difficulty encountered with the present approach appears to be an adequate treatment of polarization of the medium and the charge transfer between the local and the nonlocal region. Perfect and defective hexagonal boron nitride is used as a simple test system to check the adequacy of the underlying assumptions and to exemplify the computational problems that are encountered.
Theoretical investigation of a possible new stress-induced anthracene crystal phase with a strong effect on triplet exciton transport
Authors: Yokoi Kohei , Siebrand Willem
Published: July 2002

Exploratory calculations are reported on the structure and energy of anthracene lattices under stress. The calculations, based on atom–atom potentials of the form of 6-exp, indicate that expansion of the lattice in the ab plane, especially along b, may give rise to rotation of anthracene molecules about their long axis. It is suggested that this could result in a new phase which may be stabilized as an embedded region after release of the stress. An attempt is made to relate these deformed regions to the triplet exciton traps generated when anthracene crystals are bent. Relative triplet diffusion rates are calculated for the two phases and their boundary. Triplet diffusion in the new phase is found to be much faster than in the regular crystal, especially in the c′ direction. However, triplet diffusion across the phase boundary is calculated to be slow. These results are compared with triplet trapping data.
Vibrational selectivity in the single-photon infrared photochemistry of matrix-isolated 2-fluoroethanol
Authors: Shirk James S. , Marquardt Charles L.
Published: July 2002

Relative quantum efficiencies for the IR-induced G′g to Tt conformer interconversion of 2-fluoroethanol in solid argon are reported. Laser excitation was used to investigate ten vibrational bands of 2-fluoroethanol with frequencies between 952 and 7121 cm−1. Three bands of the deuterated (OD) analog were also investigated using laser and filtered glower excitation. Deviations of the quantum efficiencies from a smooth, monotonic function of energy were significantly larger than the experimental uncertainties. Anomalously high quantum efficiencies were found for modes with strong coupling to the COH torsion.