bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple semiclassical adiabatic calculation of anharmonic cross constants of a vibrational spectral fit
Authors: Fairen Victor , Lopez Vicente
Published: July 2002

A simple classical adiabatic procedure, implemented with an EBK semiclassical quantization, permits the calculation of first order cross anharmonic constants of a vibrational spectral fit and shows their dependence on the anharmonicity of the coupling and not on the intrinsic anharmonicity of the modes. These first order corrections are identical to those obtained with a quantum mechanical approach.
Rotational spectrum of a weakly bound dimer of formaldehyde and acetylene: Identification and characterization of a bridged planar form involving two nonlinear hydrogen bonds
Authors: Howard N. W. , Legon A. C.
Published: July 2002

Pulsed-nozzle, Fourier-transform microwave spectroscopy has been used to observe and measure the rotational spectra of the following five isotopomers of a weakly bound dimer formed between formaldehyde and acetylene: (H2CO,HCCH), (H2CO,DCCD), (H2CO,HCCD), (H2CO,DCCH), and (D2CO,HCCH). Rotational constants Av, Bv, Cv, and centrifugal distortion constants ΔJ, ΔJK, and δJ have been determined for the ground state (v=0) for all species and for a vibrationally excited state (v=1) for the first two. The values for the v=0 state in (H2CO,HCCH) are: A0=30 400.567(3) MHz, B0=2355.8304(3) MHz, C0=2180.3335(5) MHz, ΔJ =13.159(8) kHz, ΔJK =−311.4(2) kHz, and δJ =1.526(5) kHz. A detailed analysis of the rotational constants leads to the conclusion that the dimer has an unusual, bridged planar geometry, with the two subunits bound through two nonlinear hydrogen bonds. One bond has acetylene as the proton donor and the oxygen atom of formaldehyde as the acceptor while in the other a formaldehyde proton interacts with the acetylene π bond. The geometry is characterized by the following distances and angles: r=3.86(2) Å is the distance from the C atom of H2CO to the center of C≡C, θ=80.3(16)° is the angle made by the C2 axis of H2CO with r while φ=40.1(17)° is the corresponding angle made by the acetylene axis. The hydrogen bond distances are r(O⋅⋅⋅H)=2.39 Å and r(center⋅⋅⋅H)=3.12 Å. The vibrationally excited state has been identified with a motion involving the torsional oscillation of the H2CO subunit about its C2 axis. A relatively high barrier to this motion at 90° to the molecular plane is postulated.
Simple example illustrating the different parametrizations of the Mo/ller operator
Authors: Snider R. F.
Published: July 2002

Various energy and convergence factor parametrizations of the Mo/ller operator are discussed. These can usually be applied to eigenstates of the free Hamiltonian, in contrast to the Mo/ller operator itself, which is only correctly defined in Hilbert space. Formal differences of the parametrized operators are exemplified in one dimension using a particular separable potential for which all computations can be carried out analytically. The behavior of the energy parametrized operators are contrasted when the convergence parameter is taken to zero and it is shown how the parametrized operators may be consistently used if a proper interpretation of the formulas is maintained. The second virial coefficient is also examined for the particular potential and it is shown how the Mo/ller operator can be used in its evaluation.
General conditions for the occurrence of off-axis extra lines in powder-pattern ESR fine structure
Authors: Teki Yoshio , Takui Takeji , Itoh Koichi
Published: July 2002

A spin Hamiltonian consisting of the Zeeman and fine-structure terms is solved for an arbitrary spin S using third-order perturbation theory (‖D‖≪hν). From this solution, general analytical expressions are derived for the occurrence of off-axis extra lines in ESR fine structure. These appear under certain conditions in powder-pattern ESR spectra besides the canonical lines associated with principal axes of g and fine-structure tensors. The occurrence conditions, which essentially come from the second-order term in the fine-structure energy, are given for the allowed (ΔMs=±1) and forbidden (ΔMs=±2) transitions without restrictions previously assumed in the literature, viz., an axially symmetric fine-structure tensor, an isotropic g tensor, or a limited S. It is shown that extra lines tend to appear with an increasing S, an increasing fine-structure energy, and a decreasing microwave frequency. Spectral simulation also reveals that for high-spin systems (S>1) extra lines commonly appear at the X band with comparable or even stronger intensities compared with normal canonical lines, so that inclusion of extra lines is necessary for analysis of powder-pattern spectra from such systems. Diagrams illustrating the appearance area in fine-structure parameters are presented for S=3/2 to 4 and are used to analyze the data reported so far; these diagrams may greatly assist an understanding of such high-spin spectra.
Complex quasiprobability for atoms trapped on surfaces: A novel application of the complex coordinate method
Authors: Engdahl Erik , Maniv Tsofar , Moiseyev Nimrod
Published: July 2002

A novel concept of complex quasiprobability Q(x) is proposed for atoms selectively trapped on a static, corrugated surface. The real part of Q(x) is the probability that the position vector of a trapped atom will have a projection x on the nominal surface plane, while Im[Q(x)]/‖Q(x)−1‖ is a local measure of the strength of the coupling between different diffraction channels, which leads to desorption of the trapped atoms from the surface. A method of calculating Q(x), based on the complex coordinate method, is presented and discussed. Applying this method to a model atom–surface potential which includes one-dimensional steps, it is shown that while the probability to find a trapped atom is enhanced around the top of a step, desorption is most likely to occur from the middle of the terraces.
Reactive scattering and electron detachment for collisions of halogen negative ions with HCl, DCl, and HBr
Authors: Champion R. L. , Doverspike L. D. , Huq M. S. , Scott D. , Wang Yicheng
Published: July 2002

Absolute total cross sections have been measured for collisions of Cl−, Br−, and I− with HCl, DCl, and HBr for projectile energies ranging from 5 to 300 eV. The processes investigated include reactive scattering and electron detachment. The reactive scattering cross sections exhibit considerable isotope effects and the collisional dynamics are discussed within the framework of a spectator-stripping model which involves proton or deuteron abstraction. The results for the I− projectile are substantially different from those for Cl− and Br−; this difference is suggested to be related to the relative stability of the molecular anion, HI−.
Nonlinear coupling of steady state transport processes. I. Description of the global properties
Authors: Hoff Heinrich
Published: July 2002

Before extending the theory of nonlinear heat conduction to an arbitrary number of coupled processes, the representation of nonlinear global properties is discussed. A certain phenomenon, in which the separation of certain reverse osmotic systems may vanish at certain compositions, could support the concept of the nonlinear transport under discussion.
Nonlinear coupling of steady state transport processes. II. Determination of certain global properties
Authors: Hoff Heinrich
Published: July 2002

The dependence of the phenomenological coefficients on certain intensive variables, e.g., temperature, pressure, and composition, is responsible for certain nonlinear phenomena of the global properties. Some kinds of symmetry relations mentioned in a previous paper are demonstrated to be valid. Additionally, the necessary and sufficient conditions of rectification phenomena are derived.
Vibrational and electronic spectroscopy of pyridine and benzene adsorbed on the Rh(111) crystal surface
Authors: Mate C. M. , Somorjai G. A. , Tom H. W. K. , Zhu X. D. , Shen Y. R.
Published: July 2002

We report the vibrational and electronic spectra for pyridine and benzene adsorbed on the Rh(111) crystal surface obtained by high-resolution electron energy loss spectroscopy (HREELS). Low-energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), and optical second harmonic generation (SHG) have also been used to provide complementary information. Pyridine adsorption on Rh(111) was studied over the 77–450 K temperature range. At 77 K, multilayers of pyridine are observed with a vibrational spectrum similar to that of liquid pyridine. Between 185 and 230 K, HREELS and TDS indicate that both physisorbed and chemisorbed pyridine species are present on the surface. The physisorbed species desorbs at 295 K, while the chemisorbed species is stable until it decomposes on the surface at 400 K. We propose that the chemisorbed species is an α-pyridyl complex as thermal desorption spectroscopy indicates partial dehydrogenation of this pyridine surface species. Electronic energy loss spectra for both benzene and pyridine adsorbed at 310 K show only a weak transition centered at ∼4 eV. The absence of prominent π→π* transitions, which are readily observed for multilayers of benzene adsorbed on Rh(111), implies that the π orbitals are strongly involved in the chemisorption bond of these molecules with the Rh(111) surface.
Rotational tunneling of bound H2 in a tungsten complex
Authors: Eckert J. , Kubas G. J. , Dianoux A. J.
Published: July 2002

The rotational tunnel splitting of the librational ground state of activated molecular hydrogen bound in a tungsten complex has been determined to be 0.95 (1) cm−1. With the assumption of a twofold cosine potential with one degree of freedom for the rotation, this result yields a barrier height of 760 cm−1 in good agreement with the analysis of the librational data. These quantum mechanical rotations are also found to persist up to temperatures above 150 K. The relationship of these measurements to the binding of molecular hydrogen to the metal center are discussed.
State-to-state N2(A 3Σ+u) energy-pooling reactions. I. The formation of N2(C 3Πu) and the Herman infrared system
Authors: Piper Lawrence G.
Published: July 2002

We have studied the formation of N2(C 3Πu, v=0–4) and the nitrogen Herman infrared system, v′=2,3, in energy pooling reactions between N2(A 3Σ+u, v′=0–1). Our results indicate rate coefficients of (1.5±0.4) and (1.5±0.5)×10−10 cm3 molecule−1 s−1 for formation of N2(C 3Πu, v′=0–4) from the energy pooling of two N2(A,v′=0) molecules and for a v′=0 and a v′=1 molecule, respectively. We did not see evidence of significant N2(C) formation in energy pooling between two N2(A,v′=1) molecules (k<5×10−11 cm3 molecule−1 s−1). N2(A,v′=0) energy pooling produces only v′=3 of the Herman infrared system with a rate coefficient of ≥(8.1±2.3)×10−11 cm3 molecule−1 s−1. Energy pooling between N2(A,v′=0) and N2(A,v′=1) produces only v′=2 of the Herman infrared system with a rate coefficient ≥(9.9±2.9)×10−11 cm3 molecule−1 s−1. Again, energy pooling between two N2(A,v′=1) molecules results in no significant contributions to the Herman infrared system. The participation of N2(A) vibrational levels ≥2, however, does result in excitation of the lower-lying vibrational levels of the Herman infrared system.
Ammonium perchlorate structure and dynamics at low temperatures
Authors: Prask H. J. , Choi C. S. , Chesser N. J. , Rosasco G. J.
Published: July 2002

Single-crystal and powder neutron diffraction, coherent neutron inelastic scattering, and Raman spectroscopy have been used to study the low temperature structure and dynamics of ammonium perchlorate. No evidence for a phase transition is found. Based on analysis of thermal motion amplitudes and inelastic neutron-scattering data for ND4ClO4 a Raman-active B3g symmetry zone-center mode at 45 cm−1 is identified as a libration. Another Raman-active mode, B1g symmetry at 33 cm−1, and a previously unobserved Au symmetry mode at 12 cm−1, are inferred to have significant librational character at q=0. Comparison of these results with earlier incoherent neutron scattering results suggests that, because of the low activation energy of ammonium ions, classical jump reorientations strongly influence ammonium-ion sublattice dynamics even to temperatures as low as 20 K. Partial dispersion curves are also presented.
Resonance polarization CARS of pyrene in the lowest excited singlet state
Authors: Kamisuki Toshio , Takeuchi Shinsuke , Akamatsu Naotoshi , Adachi Yukio , Maeda Shiro , Hirose Chiaki
Published: July 2002

Polarization CARS of pyrene in the S1 state has been observed in solution at room temperature under the resonance condition with the Sn←S1 transient absorptions. The polarization behaviors of totally symmetric ag and nontotally symmetric b1g modes have been interpreted on the basis of an irreducible tensor formulation of the polarization CARS susceptibility which is applicable rigorously in resonance conditions, and anomalous depolarization ratio for the b1g mode corresponding to the case of ρl >3/4 in spontaneous Raman scattering has been deduced.
Physics of reacting particle swarms. II. The muon-catalyzed cold fusion cycle
Authors: Robson R. E.
Published: July 2002

Multiple fusion reactions in a deuterium–tritium mixture catalyzed by a swarm of muons are analyzed by means of momentum-transfer theory along the lines of the general discussion given in Ref. 7. Energy balance equations for the various reactants are derived and are solved for a particular set of model cross sections, for several mixture temperatures, and tritium fractions. Maximum cycling rate occurs for temperatures near 1600 K and for a tritium fraction of 0.6.
Production and loss of CF2(3B1) in the O+C2F4 reaction
Authors: Young R. A. , Blauer J. , Bower R. , Lin C. L.
Published: July 2002

Low pressure fast flow measurements of the emission from CF2(3B1) generated in mixtures of O with C2F4 in Ar and similar measurements using the air afterglow to follow oxygen atoms were made. From measurements of the exponential decay of air afterglow emission, it is concluded that the reaction proceeds through a C2F4O* intermediary. From the intensity and time evolution of the CF2(3B1) emission it is found, contrary to existing belief, that the yield of CF2(3B1) is small (less than 1%) and its radiative lifetime is much shorter than 1 s. The overall loss of O atoms at low C2F4 densities is characterized by a rate constant of 1.2×10−12 cm3 s−1. Both NO and O2 strongly quench the CF2(3B1) while quenching the precursor much less effectively. C2F4 quenches the precursor regenerating O, but does not quench CF2(3B1) significantly.
Excess energy dependence of internal conversion in the S1 state of azulene
Authors: Kulkarni Sudhir K. , Kenny Jonathan E.
Published: July 2002

The internal conversion (IC) rates for nine single vibronic levels of the S1 state of azulene, having from 0 to 2417 cm−1 of vibrational energy, have been measured by direct absorption spectroscopy in a pulsed, planar supersonic jet. The value of kIC at the vibrationless level is 9.4×1011 s−1 , with an approximately linear increase to 3.3×1012 s−1 at the highest level studied. This excess energy dependence of the rate constant is contrasted to that for S2 →S1 IC across an almost identical electronic energy gap, and an explanation involving low-frequency modes is offered.
Core level photoemission of iodine overlayers
Authors: Dowben P. A. , Kime Y. J. , Mueller D. , Rhodin T. N.
Published: July 2002

We report the core level binding energies of chemisorbed iodine on Fe(110) and Fe(100). A decrease of 0.6 eV in the binding energies of the iodine core levels is observed with the increasing coverage of the chemisorbed iodine overlayer. This change in core level binding energies with coverage is compared with the results for iodine overlayers on other transition metal surfaces. The difference in core level binding energies between chemisorbed iodine on Fe(110) and molecularly adsorbed iodine on Fe(110) is explained using a Born–Haber cycle and an ‘‘equivalent’’ cores approximation.
Concentration dependent translational friction coefficient of cyclic polymers in dilute solutions
Authors: Alessandrini Jose Luis , Fatur Alejandro
Published: July 2002

The leading concentration dependence of the translational friction coefficient of long cyclic polymers is evaluated in the framework of the cluster expansion method. It is found that excellent agreement is achieved with recent quasielastic light scattering experiments on linear and cyclic polystyrene macromolecules.
Vibrationally resolved electronic autoionization of core–hole resonances
Authors: Poliakoff E. D. , Kelly L. A. , Duffy L. M. , Space B. , Roy P. , Southworth S. H. , White M. G.
Published: July 2002

We investigate the dynamics of molecular core–hole decay using dispersed fluorescence from an ionic valence–hole state in N2. A core–hole excited state is created via the N2(1s→1 π*g) transition, and this state electronically autoionizes to the N+2(B 2Σ+u) state. The vibrational branching ratios for the N+2(B 2Σ+u) state are then determined from N+2(B 2Σ+u→X 2Σ+g) fluorescence. Fundamental aspects of core–hole state decay emerge clearly from these measurements. In particular, interference effects due to lifetime broadening of vibrational levels of the core–hole state can be investigated quantitatively using this method. As a result, dispersed fluorescence detection serves as a powerful tool for investigating R-dependent aspects of molecular core–hole resonances. The experimental results do not agree with predictions based on previous theoretical developments, and possible causes for the discrepancy are discussed.
Cluster expansion in density for the dielectric constant of a colloidal model suspension
Authors: Vogel E. , Pauly H.
Published: July 2002

In order to describe the dielectric response of a dense suspension of polarizable spherical particles to an external low frequency field one has to find an appropriate expansion in density. Beyond the Clausius–Mossotti formula, which only is a mean field ansatz, a cluster expansion (Ref. 1) takes account of the interaction between particles. The one-particle–dipole polarizability being given, the terms up to second order in density including two-particle interaction can be calculated. With the help of this enhanced dipole-residual-interaction model the dispersion (low frequency response) of colloidal suspensions can be discussed more thoroughly than before.
Vibrational circular dichroism and vibrational optical rotatory dispersion in molecular crystals. IV. Overtones of degenerate vibrations
Authors: Lalov I. J. , Kotzev J. N.
Published: July 2002

Two-quanta anharmonic spectra, namely overtones and combination bands with degenerate vibrations, in uniaxial gyrotropic crystals from point group of symmetry C3, D3, C4, D4, are investigated, with due account taken of the time inversion. The symmetry of two-phonon states is studied. A general model of the anharmonicity and the influence of the crystal chiral structure on intermolecular exchange of the circularly polarized degenerate vibrations is elaborated. The contribution of overtones and of the combination bands to dielectric permittivity tensor, and to the gyration tensor is studied too. The paper also deals with the IR and vibrational circular dichroism (VCD) spectra near the frequencies of the unbound and of the bound two-phonon states as well as the general features of two-phonon circularly polarized states appearing in the linear and in nonlinear optical processes in gyrotropic crystals.
Application of the multiconfiguration time-dependent Hartree–Fock method to CH+: The auxiliary active space
Authors: Jaszuński Michal/ , Rizzo Antonio , Yeager Danny L.
Published: July 2002

The multiconfigurational time-dependent Hartree–Fock (MCTDHF) method is used to study the excitation energies and transition moments of the CH+ ion. A consistent approach to the selection of configurations based on the complete active space (CAS) model is successfully applied. In this approach a large set of orbitals is included in the active space without a substantial increase in the number of configurations, since only for a smaller subset of orbitals is the configuration expansion complete and the remaining orbitals active are considered an auxiliary set. For CH+ the active space includes the valence and additional orbitals, with the valence orbitals constituting the complete subset. Extra configurations involving single and double excitations from the valence to the additional (auxiliary) orbitals are included both for the MCSCF reference state and in the MCTDHF. It is demonstrated that this active space accurately mimics MCSCF and MCTDHF calculations with an enlarged complete active space which includes both the original CAS and the auxiliary orbitals. The calculations for the 1 Π and 1 Σ+ excited states at the equilibrium geometry show that accurate excitation energies and transition moments are obtained in this way. For most of these states for which there are other good ab initio results available, we obtain comparable excitation energies and transition moments. In addition to 1 Π and 1 Σ+, low lying states of other symmetries are obtained and discussed.
The rotational energy accommodation of NO formed in the catalytic oxidation of NH3 over Pt(111)
Authors: Hsu D. S. Y. , Squire D. W. , Lin M. C.
Published: July 2002

Rotational energy distributions of the desorbing NO product from the NH3+O2 reaction on a Pt(111) single crystal have been measured using the laser-induced fluorescence technique in conjunction with an UHV apparatus. Over the surface temperature range 800–1300 K, the rotational temperature of NO was found to remain virtually constant near 400 K.
Internal resonances for energy flow in collisionally perturbed symmetric van der Waals complexes near fragmentation threshold
Authors: Shin H. K.
Published: July 2002

Classical trajectory calculations and analysis of collision-induced energy flow near the fragmentation threshold in a symmetric van der Waals complex of the type BL⋅⋅⋅X2⋅⋅⋅BR, in which two weak bonds are separated by a molecular unit, are presented. The collision of an incident atom with BL results in transfer of a large fraction of translational energy to the complex and most of the energy is found to be localized on the right-hand side bond X2⋅⋅⋅BR. Though the amount of energy transferred to the complex greatly exceeds the sum of van der Waals bond strengths, the total fragmentation does not occur until internal resonances between BL⋅⋅⋅X2 and X2⋅⋅⋅BR bonds cease. Between the fragmentation thresholds of X2⋅⋅⋅BR and BL⋅⋅⋅X2, there is a tendency for BL⋅⋅⋅X2 to stabilize through internal resonant exchange of energy.
On the structure of the liquid metal–polar adsorbate interface: Monte Carlo simulations
Authors: Cai Zhong-Hou , Harris Jonathan , Rice Stuart A.
Published: July 2002

We show, by use of self-consistent Monte Carlo simulations, that contact between a liquid metal and a polar adsorbate alters the longitudinal density distribution in the liquid metal side of the interface. In particular, the amplitude of modulation of the stratification of the metal in the interface is increased by the polar adsorbate, which will lead to changes in the work function, transverse electrical conductivity, etc. The results of calculations of the x-ray reflectivity as a function of angle of incidence on the liquid metal–polar adsorbate interface suggest that the change induced in the interface longitudinal density distribution of the metal is measurable.
Structure of polyacetylene–iodine complexes
Authors: Murthy N. S. , Miller G. G. , Baughman R. H.
Published: July 2002

We confirm the existence of a 15 Å period in iodine-doped polyacetylene and provide a new interpretation for this key feature as part of a general model for structural changes during iodine doping. The observed diffraction intensities for different samples suggest the existence of structures with two different types of dopant-containing layers: layers obtained by complete replacement of polyacetylene chains by iodine columns (F layers) and layers obtained by replacement of every other polyacetylene chain by an iodine column (P layers). The F layers in the heavily doped complex alternate with dopant-free layers of polyacetylene chains (U layers), corresponding to a (UF)n stacking sequence. The phase obtained at a lower dopant concentration, which provides the 15 Å spacing, is attributed to a (UPUF)n stacking sequence. At still lower dopant concentrations, one obtains a (UP)n stacking sequence. This model, along with published Raman, Mössbauer, and photoelectron spectroscopy data, suggests that the ratio of I−5 to I−3 increases in going from P layers to F layers. Intense and monotonically decreasing, diffuse x-ray scattering suggests that vacancies of size ∼3 Å are present, probably in iodine columns. A diffuse reflection at 3.1 Å, observed in all iodine-doped samples, is due to an average iodine–iodine distance in disordered columnar arrays. On the other hand, ordered arrays of iodine columns in oriented samples give rise to sharp meridional reflections. All ten observed reflections (down to 1.17 Å) in one sample could be indexed based on a 33.8 Å repeat corresponding to (–I−3–I−5–I−3–)n arrays. The observed diffraction pattern was calculated from this model without using any freely adjustable parameters.
Reorientation of benzene in its crystalline state: A model case for the analogy between nuclear magnetic resonance spin alignment and quasielastic incoherent neutron scattering
Authors: Fujara F. , Petry W. , Schnauss W. , Sillescu H.
Published: July 2002

The close analogy between 2H-NMR spin alignment and 1H quasielastic incoherent neutron scattering [J. Chem. Phys. 84, 4579 (1986)] in determining the geometry and time scale of molecular reorientation is illustrated by an experimental example. Analysis of the final states of both methods show consistently that benzene in its (poly)crystalline state reorients by rotational jumps about the molecular sixfold symmetry axis. Emphasis is put on the quasielastic structure factor of incoherent neutron scattering, which excludes random jumps among the six orientations as the reorientation mechanism, allowing only single rotational jumps.
Bistability in isothermal photochemical systems: The A⇄hνB→hνC reaction in a continuous flow stirred tank reactor
Authors: Laplante J. P. , Lavabre D. , Micheau J. C.
Published: July 2002

In this paper we present a kinetic analysis of the consecutive photoreaction scheme A⇄hνB→hνC assuming the reaction is carried out in a continuous flow stirred tank reactor (CSTR). The reactor is kept at constant temperature and fed with reactant A at a constant flow rate. A numerical analysis of the model’s stationary states reveals a range of constraints for which the system possesses multiple steady states. The observed bistability depends strongly on the rate constant of the B→A reaction k2 . It is typically observed when k2 is much larger than the other rate constants. Our numerical calculations also reveal a marked dependency on parameters such as the molar absorptivities and the irradiation intensity I0 . Interestingly, multiple steady states are only observed for intermediate values of I0 . Analytical approximations are obtained for the stationary states in the limit where the end-product C does not absorb light. These approximations are used to clarify the mechanism responsible for the light-induced instability.
Vibrational study of phase transitions in (CH3)3NHNO3
Authors: Mylrajan M. , Srinivasan T. K. K.
Published: July 2002

(CH3)3 NHNO3 belongs to the monoclinic system with space group P21/c (C52h ) with four molecules per unit cell. Raman and infrared spectra (10–5000 cm−1) of single crystals and polycrystalline samples of (CH3)3 NHNO3 and of its N-deuterated derivative were investigated in the temperature range 90–415 K. Assignments of the measured frequencies to the internal vibrational modes were obtained. A systematic temperature dependent study of frequencies, bandwidths and integrated intensities was performed. The results indicate the existence of phase transitions at 359 and 407 K and both phase transitions show thermal hysteresis, characteristic of first order. In the high temperature phases II and I, the cations and anions achieve reorientational motion.
Molecular spectra in chaotic regime expressed by the Wigner function
Authors: Xie Bomin
Published: July 2002

We have shown in this paper that the rovibrational spectrum of a molecule corresponding to the classical chaotic regime can be expressed by the dipole correlation averaged over the Wigner function, and that the commonly used dipole correlation averaged over the classical microcanonical ensemble is not generally valid in the chaotic regime. The spectacular characteristics of chaotic trajectories, e.g., the exponential growth of separation of initially nearby trajectories, the decaying correlation, etc., make the molecular spectra diffuse and obscure its line structure. It is suggested that the correlation expression obtained in this paper may be used to construct the approximate envelope of the actual spectra.
Semiclassical quantization by circuit counting: Application to SO2
Authors: Mehta Manish A. , De Leon N.
Published: July 2002

In this paper a semiclassical quantization method is developed whose formulation and application is simple, general and accurate. We call this method semiclassical quantization by circuit counting (SQCC). SQCC is based upon evaluating the action integral along a trajectory until it undergoes a near recurrence. Several near recurrences are used to obtain a set of independent equations which can then be inverted to yield the actions for the trajectory. Once the actions are obtained a linear extrapolation is used to calculate semiclassical energies. We apply the method to two model systems: (1) three uncoupled Morse oscillators and (2) a realistic three degree of freedom model of SO2. SQCC is found to work very well for these systems. We discuss some of the advantages and disadvantages of SQCC and its application to systems with more than three coupled molecular degrees of freedom.
A photodissociation study of 1,3-butadiene
Authors: Sellers-Hann L. , Krailler R. E. , Russell D. H.
Published: July 2002

Laser-ion beam photodissociation is used to study the C4H+6 radical cation formed by electron impact (70 eV nominal energy) ionization of 1,3-butadiene. The kinetic energy release value obtained from C4H+6→C3H+3+CH3 does not agree with the distribution reported by Farrar [J. Chem. Phys. 77, 263 (1982)]. The photodissociation studies of C4H+6 suggest the existence of a long-lived (>0.05×10−6 s) photoexcited C4H+6 ion. Also, results of photodissociation studies of C4H+6 trapped in the electron beam space charge are consistent with the proposed long-lived photoexcited C4H+6 ion. Therefore, it is proposed that the two-photon photodissociation of C4H+6 reported by Baer [J. Chem. Phys. 85, 6361 (1986)] is a sequential two-step process involving a long-lived excited C4H+6 ion.
The surface excess of electric polarization at electrified interphases
Authors: Aloisi G. , Foresti M. L. , Guidelli R.
Published: July 2002

It is known that the thermodynamic properties of electrified interphases between metals and dilute solutions of nonspecifically adsorbed 1–1 valent electrolytes, once corrected for the so called ‘‘diffuse layer’’ on the basis of the Gouy–Chapman (GC) theory, yield pseudothermodynamic quantities which are independent of the electrolyte concentration. It is shown that, as a line of principle, the latter quantities can be interpreted on the basis of molecular models of the interphase from which ions are excluded. To this end a ‘‘polarization surface excess’’ is introduced for which analytical expressions are provided both for nonprimitive dipole–wall models in the framework of the mean spherical approximation and for monolayer lattice models in the framework of the mean field approximation. Predictions of these two different models are critically compared.
Hyperfine predissociation of the B state of Cl2
Authors: Billy N. , Girard B. , Gouédard G. , Vigué J.
Published: July 2002

Thanks to lifetime measurements, we give evidence of a predissociation of the v≥13, J=0 levels of the B state of Cl2. This weak predissociation is interpreted as a hyperfine predissociation, comparable to the ones observed in Br2 and I2. Moreover, the radiative lifetime of the v=12 level has been found closed to 1200 μs.
Nuclear spin relaxation in NH4ClO4 and ND4ClO4
Authors: Bastow T. J. , Brown R. J. C. , Segel S. L.
Published: July 2002

Spin–lattice relaxation times for chlorine and deuterium isotopes in NH4ClO4 and ND4ClO4 have been measured over the temperature range 153 to 295 K. No evidence in support of the hypothesis that there is a phase transition near 180 K has been found in the results.
Reply to ‘‘Nuclear spin relaxation in NH4ClO4 and ND4ClO4’’
Authors: Verma A. L. , Chakraborty T.
Published: July 2002

The 180 K phase transformation in NH4ClO4 could not be detected by measurements of spin–lattice relaxation times for chlorine and deuterium isotopes by Bastow et al. due to much slower time scale of this technique.
Interaction of hexafluoroazomethane with Si(111)
Authors: McFeely F. R. , Yarmoff J. A. , Beach D. B.
Published: July 2002

Chemisorption of hexafluoroazomethane on Si(111) was studied with synchrotron photoemission as a model system for studies of halocarbon-based etching. C 1s, N 1s, and F 1s core level spectra were collected for various room temperature exposures of clean silicon to hexafluoroazomethane, and after mild annealing. The initial reaction of hexafluoroazomethane with silicon is shown to be quite complex, resulting in the formation of many adsorbed dissociation products. Annealing resulted in the desorption and decomposition of these species. These results demonstrate the buildup of a passivating carbon layer on the silicon samples, which may be responsible for the inability of CFx radicals to etch silicon effectively.
Mechanisms of the L′ 2Φ–X 2Π emission of NO in Ar and Kr matrices
Authors: Chergui Majed , Schwentner Nikolaus , Chandrasekharan Venkataraman
Published: July 2002

New time and energy resolved spectra of the L′ 2Φ–X 2Π (0,v″) bands of NO in Ar and Kr matrices are reported. The L′(0,v″) bands are excited exclusively via the B′ 2Δ valence state and their lifetime is 3000±500 ns in both matrices. The quantum efficiency for L′(v=0) emission is estimated to be ≤0.04. The 2Φ–2Π transition is discussed in terms of a statically induced transition moment involving spin–orbit mixing with B′ 2Δ, but also in terms of nonadiabatic matrix elements due to the coupling to the lattice. Relaxation down to L′(v=0) is discussed in terms of matrix-induced interstate cascading with the b 4Σ− state.
Crossed molecular beam studies of the reactions of methyl radicals with iodoalkanes
Authors: Robinson Gary N. , Nathanson Gilbert M. , Continetti Robert E. , Lee Yuan T.
Published: July 2002

The I atom exchange reactions, CH3 +RI→CH3 I+R[R=CF3 , (CH3 )3 C], were investigated at a collision energy of ≈13 kcal/mol using the crossed molecular beams technique. The supersonic beam of methyl radicals was formed by pyrolyzing a mixture of ≈1% di-tert-butyl peroxide in helium in a quartz nozzle. A large fraction of the total energy available to the products from these reactions is channeled into relative translation [≈50% for R=(CH3 )3 C and ≈70% for R=CF3 ] suggesting that the dominant interaction among the products is repulsive. The CH3 I product from both reactions was observed to be entirely backward scattered with respect to the incident radical beam indicating that a roughly collinear C–I–C transition state geometry is favored. The present results are compared to those of earlier crossed beam studies of the CH3 +IY→CH3 I+Y(Y=Cl, Br, I) reactions; the differences observed among these reactions are explained with reference to the CH3 I–Y and CH3 I–R interaction potentials.
The first-order concentration dependence of the mutual diffusion coefficient of Brownian particles
Authors: Yoshida Nobuo
Published: July 2002

The first-order concentration dependence of the mutual diffusion coefficient of spherical Brownian particles in a suspension has previously been calculated essentially within the framework of the Smoluchowski equation in the configuration space of a pair of particles. After these calculations are reviewed, the same quantity is here treated on the basis of the Fokker–Planck equation in the phase space of a pair of particles which is considered to have a wider range of validity than the Smoluchowski equation. Two methods are used in the treatment. In one method the mobility of the particles is determined by solving the Fokker–Planck equation in a stationary state which is reached by application of the same external force on each particle. In the other method a known expression for the mobility in terms of time-correlation functions is evaluated by solving the time-dependent Fokker–Planck equation in the absence of external forces. The mobility thus obtained is transformed into the diffusion coefficient with the aid of the generalized Einstein relation. It is found that both methods lead to the same result for the diffusion coefficient as derived from the Smoluchowski equation. Implications of the present calculations are also discussed.
Surface enhanced two photon absorption near a small metal particle
Authors: Das Purna C. , Metiu Horia , Puri Ashok
Published: July 2002

We examine a quantum mechanical model for two photon absorption by a molecule near a spherical metal particle. The adsorbed molecule is idealized as a three level system and the metal particle is taken to represent a ‘‘rough surface.’’ Expressions for the second order nonlinear dipole moment of the adsorbed species are obtained. Since the nonlinear optical power absorption is directly proportional to the square of the respective nonlinear dipole moment, one is able to draw conclusions regarding the effect of the substrate on nonlinear absorption by the adsorbate. Peak enhancement of surface induced two photon absorption is predicted for a molecule–surface separation of ≈20 Å. Optimum conditions for maximum enhancement are investigated.
Low frequency pulse excitation in zero field magnetic resonance
Authors: Kreis R. , Thomas A. , Studer W. , Ernst R. R.
Published: July 2002

Zero field magnetic resonance experiments using semiselective excitation by low frequency pulses are analyzed. The prospects of phase cycling experiments in zero field are discussed and the differences between excitation by low frequency and direct current pulses are outlined. It is demonstrated that despite the selectivity of excitation all three transitions in a three-level system are observed. Deuterium quadrupolar resonance and computer simulations are employed to verify predictions.
Dynamics of endoergic substitution reactions. II. Br+{C2H2Cl2}→Cl+{C2H2ClBr}
Authors: Robinson Gary N. , Continetti Robert E. , Lee Yuan T.
Published: July 2002

We have extended the crossed beams studies described in the preceding paper to the reactions of Br atoms with 1,1- and trans-dichloroethylene. The shapes of the product translational energy distributions and excitation functions for both reactions support our previous conclusion that Cl elimination from Br–R–Cl collision complexes can compete with Br elimination only in the limit that few vibrational modes of the complex are active in energy redistribution. The substitution cross section for the Br+CH2CCl2 reaction is considerably lower than that for the Br+trans-CHClCHCl reaction in the collision energy range 15–25 kcal/mol, suggesting that steric effects play a dominant role in determining the relative magnitudes of the cross sections.
Upon the application of cumulant analysis to the interpretation of quasielastic light scattering spectra
Authors: Phillies George D. J.
Published: July 2002

Monte Carlo simulations were used to study how noise limits the interpretation of quasielastic light scattering spectra with cumulant analysis. The effects of signal-to-noise ratios, channel spacing, line shape, and the truncation order of the cumulant series were all examined. The underlying spectra included narrow and broad unimodal and bimodal forms, as expected for ternary polymer:polymer:solvent mixtures. The upper bound on the usable number of cumulants is determined by the signal-to-noise ratio, the spectral nonexponentiality, and the number and spacing of the spectrometer channels. Upper limits on the acceptable degree of spectral nonexponentiality—below which the cumulant expansion is useful—can be stated in terms of the measured second cumulant. Use of logarithmically rather than linearly spaced correlator channels greatly increases the region over which cumulant fits are useful.
Charge transfer interaction between a pair of electronically excited moieties: Very slow charge neutralization of intramolecular ion pairs formed by biphotonic excitation of diarylmethanes
Authors: Modiano Steven H. , Locke R. J. , Lim E. C.
Published: July 2002

It is shown that biphotonic excitation of diarylmethanes leads to the formation of ion pairs with extremely long time scale of charge recombination.
Counterion unbinding in a micellar liquid crystal in the presence of an alcohol
Authors: Li Zili , Rosenblatt Charles
Published: July 2002

Conductivity measurements were performed on the micellar liquid crystal cesium perfluorooctanoate and water near the nematic–isotropic phase transition. Based upon a modified Debye–Hückel–Onsager model, the number of unbound counterions per micelle z− was obtained as a function of temperature and added alcohol concentration. It was found that the unbinding fraction α (≡z−/s, where s is the micelle aggregation number) decreased weakly as the disk-shaped micelles grew in size.
Diffusion controlled reactions: Experimental verification of the time-dependent rate equation
Authors: Periasamy N. , Doraiswamy S. , Venkataraman B. , Fleming G. R.
Published: July 2002

The transient effect in a diffusion limited reaction is described by a time-dependent rate coefficient: k(t)=a+b exp(c2t)erfc(ct1/2), where a, b, and c are expressed in terms of the diffusion coefficient (D), the encounter distance (R), and the absolute rate coefficient (ka); and for ionic reactions, the Onsager length (rc). Time resolved fluorescence quenching studies on cresyl violet–potassium iodide system in water confirm the validity of the above equation. The values of D and R obtained from the fluorescence quenching studies are in good agreement with the values inferred from other sources, and the value of ka is reasonable.
Physics of reacting particle swarms. III. Effects of ionization upon transport coefficients
Authors: Robson R. E. , Ness K. F.
Published: July 2002

An extended ‘‘momentum-transfer’’ approximation is applied to momentum and energy balance equations describing ionizing particle swarms in neutral gases. ‘‘Ionization cooling’’ is discussed and special attention is paid to the way in which ionizing collisions influence transport coefficients. Solutions of these equations for certain model cross sections yield swarm parameters which are in good semiquantitative agreement with results derived from accurate solutions of Boltzmann’s equation.
High pressure Raman spectra and pressure-induced phase transitions of β-9,10-dichloroanthracene
Authors: Brillante A. , Della Valle R. G. , Syassen K.
Published: July 2002

The effect of pressure on Raman spectra and optical absorption of β-9,10-dichloroanthracene crystals has been investigated in a diamond anvil cell up to 8 GPa hydrostatic pressure. Two pressure-induced phase transitions at about 3 and 5 GPa are observed, the latter being associated with a large red shift of the absorption edge of the first π*←π transition. The structure of the high pressure phases is discussed on the basis of symmetry considerations.
Time domain reflectometry study of fast-ionic-conducting glasses
Authors: Chryssikos G. D. , Burns A. , Cole R. H. , Risen W. M.
Published: July 2002

Dielectric data on model fast-ionic-conducting glasses are reported at various sub-Tg temperatures. A transformer bridge was used from 100 Hz to 200 kHz, while data between 85 MHz and 2 GHz were obtained by time domain reflectometry. Substantial improvements in the sensitivity and equivalent frequency range of the latter correct previous preliminary results reporting the existence and temperature dependence of apparent dielectric permittivity plateaus in the upper MHz spectral region of glasses.
Structure dependent competition between multiphoton absorption and intramolecular energy redistribution in organomolybdenum compounds: State selective production of molybdenum atoms
Authors: Samoriski Brian , Chaiken J.
Published: July 2002

We have measured one color multiphoton dissociation/ionization spectra (MPD/MPI) across the one photon region 23 809 to 28 735 cm−1 for a structurally homologous series of organomolybdenum molecules including: (η6-cycloheptatriene)Mo(CO)3, Mo(CO)6, and a variety of (η6-arene)Mo(CO)3-type molecules. The degree of observability of the 7DJ, 7P0J, and 7S3 Rydberg series is observed to be a function of: (1) the number of low frequency vibrations associated with the molecular precursor, and (2) the degree of localization of the cyclic ligand to metal bond. These Rydberg series are taken as a simple but sensitive probe of the production of ground state metal atoms. The efficiency for MPD production of 7S3 molybdenum atoms relative to (η6-benzene)Mo(CO)3 increases in the order 1:1.9:11 with addition of a methyl substituent and extending it to an ethyl group. These observations are qualitatively and quantitatively in good agreement with previously reported relative efficiencies of MPD/MPI of organochromium molecules to produce ground state chromium atoms.
Dynamical theory of electron transfer: Inclusion of inner-shell reorganization
Authors: Mikkelsen K. V. , Ratner Mark A.
Published: July 2002

The dynamical formulation of electron transfer rate theory, including inner sphere and outer sphere reorganization terms, electronic structure polarization, and an ab initio treatment of the electrons on donor, acceptor, and bridge molecules, is presented and applied to electron transfer betwen benzene/anion radical and pyridine. The formulation involves the use of mean field (Ehrenfest) relations to obtain the time evolution of electron and vibration operators. This formulation yields an effective density matrix for the time evolution of the electronic system; the elements of this density matrix depend on averages over electronic and vibrational motions. For the electron transfer system actually studied, the rates are strongly dependent upon relative geometry of donor and acceptor, and maximize sharply at geometries such that electronic levels on donor and acceptor become degenerate—the so-called ‘‘coincidence event’’ geometry.
Molecule–surface dissociative scattering of n-C3F7NO from MgO(100) at hyperthermal energies: Nascent NO (X 2Π)
Authors: Kolodney E. , Baugh D. , Powers P. S. , Reisler H. , Wittig C.
Published: July 2002

The title reaction was examined for incident kinetic energies in the range 3–7 eV and surface temperatures in the range 500–800 K; dissociation probabilities as high as 3±1% were measured. NO state distributions were obtained near the specular angle using two-photon, two-frequency laser ionization, and spin–orbit ‘‘temperatures’’∼170 K were observed, in contrast to higher rotational excitations. Possible mechanisms are mentioned.