bluuebunny/crossref_metadata_2025 huggingface dataset:
The microwave spectrum of the trifluoromethyl radical
Authors: Endo Yasuki , Yamada Chikashi , Saito Shuji , Hirota Eizi
Published: February 2003

The microwave spectrum of the trifluoromethyl radical in the ground 2A1 state has been observed by using a source frequency modulation spectrometer. The CF3 radical was generated directly in the absorption cell by a glow discharge in trifluoroacetic acid anhydride (CF3CO)2O. The observed transitions included N = 4 ← 3, 5 ← 4, and 6 ← 5, all of which are resolved into K as well as fine and hyperfine structure components. A magnetic hyperfine Hamiltonian was derived for three identical nuclei with a spin of 1/2 (the fluorine nuclei) in a doublet symmetric-top molecule, in order to analyze the observed spectrum. Most of the hyperfine structure could be explained by considering the total nuclear spin operator I0 = 𝒥iIi, except for the K = 1 transitions; some of them were clearly resolved into doublets and the observed splittings allowed us to determine the additional dipole–dipole hyperfine interaction constant ‖ Taa−Tbb ‖. The rotational constant B0 was determined to be 10 900.9118(52) MHz, with 2.5 times the standard error given in parentheses, and the unpaired π-electron spin density on each fluorine atom was estimated to be 12.3% from the observed hyperfine coupling constants.
The theory of photon echoes for strongly coupled electron–phonon systems
Authors: Skinner James L.
Published: February 2003

We calculate the photon echo decay for a strongly coupled electron–phonon system, without making unrealistic assumptions about excitation pulse durations. We find that asymptotically, the photon echo decay is exponential, and we provide a formal expression for the decay rate 1/T2 which is independent of pulse duration. In contrast to the usual results, our expression for 1/T2 is nonperturbative in the electron–phonon interaction. We calculate the dependences of the echo amplitude on pulse power and duration, finding that the strong electron–phonon coupling modifies the simple two level system result. We also focus on the relationship between the zero phonon line shape in the homogeneous optical absorption spectrum, and the photon echo decay rate. We find that the zero phonon line shape is Lorentzian, with width 1/πT2. We show that the usual optical Bloch equation approach to analyzing time-domain experiments, which normally is only applicable if the electron–phonon coupling is weak, can be extended to the case of strong coupling. These strong coupling Bloch equations are adequate for analyzing the time dependence, but not the pulse power and duration dependences, of time-domain experiments. Our results indicate that within the Condon approximation, electron–phonon coupling cannot explain the very low temperature anomaly of recent photon echo experiments on impurities in molecular crystals.
The rate of the reaction D+H2(v = 1)→DH+H
Authors: Glass G. P. , Chaturvedi B. K.
Published: February 2003

The rate constant of the reaction D+H2(v = 1)→DH+H has been measured at 297 K as (9.8±3.0)×10−13 cm3 s−1. The reaction was studied using a discharge flow apparatus equipped for EPR detection of small free radicals. H2(v = 1) was generated using electric discharge techniques. Previous theoretical and experimental studies have been discussed.
The dynamics of laser-induced infrared multiphoton isomerization in substituted cyclobutenes–butadienes
Authors: Buechele J. L. , Weitz Eric , Lewis F. D.
Published: February 2003

Clean isomerization between a number of cyclobutenes and their corresponding butadienes has been induced via multiple photon infrared absorption. Appropriate choices of laser frequency allow the reaction to be pushed in either direction, even though the cyclization reaction is typically 10 kcal and 4 e.u. thermodynamically disfavored. A significant dependence of yields on fluence and added inert gas pressure is observed. A simple rate equation model is developed which reproduces the major experimental observations regarding the system. Absorption cross sections, a necessary parameter for the rate equation model, are measured both calorimetrically and photoacoutically. The absorption cross section does not vary significantly as a function of laser fluence implying that absorption cross sections for successive photon absorption processes are essentially constant. The measured absorption cross section is also very similar in magnitude to the absorption cross section taken from the infrared spectrum of the compound at the laser frequency. No pressure effects on the absorption cross section are observed over the pressure range studied.
The overtone spectrum of acetylene: A rotational analysis based on a local model description
Authors: Henry Bryan R. , Mohammadi M. Ali , Tarr Allan W.
Published: February 2003

The local mode model is extended to account for the rotational structure in the CH-stretching overtone spectrum of acetylene from ΔvCH = 2 to 5. A local mode Hamiltonian, which includes nonrigidity and the resultant effects of rotation–vibration interaction, is derived and used as the basis for the analysis. The analysis indicates a strong interaction between CH bending and stretching which decreases as vCH increases. The change in equilibrium CH bond length with increasing vCH is obtained and an interesting anomaly at ΔvCH = 5 is identified.
Detection of photofragments by multiphoton ionization with direct resolution of angular and time-of-flight distributions
Authors: Rockney Bennett H. , Grant Edward R.
Published: February 2003

In the first application of resonant multiphoton ionization as a spatially and temporally resolved probe of photofragmentation dynamics, we have determined the angular and velocity distributions of CH3 and NO2 products scattered by infrared multiphoton dissociation of CH3NO2 in a skimmed, supersonic molecular beam. Our experiemental procedure rotates the focus of the vertically incident MPI probe beam in the plane of crossed infrared laser and molecular beams, 5 mm from the scattering center. Product detection occurs only within the focal volume of the probe laser yielding a solid angle resolution for the present arrangement of 0.01 steradians. From the data we offer a preliminary estimate of 3000 cm−1 as the average energy released in center-of-mass recoil for infrared laser-induced decomposition of nitromethane.
Comparison of proton transfers in heterodimers and homodimers of NH3 and OH2
Authors: Scheiner Steve
Published: February 2003

A b initio molecular orbital methods are used to study proton transfers in the cationic heterodimer (H3NHOH2)+ as well as the symmetric homodimers (H2OHOH2)+ and (H3NHNH3)+. All calculations are carried out at the Hartree–Fock level with a 4-31G basis set to ensure consistency. For proton transfers along a linear hydrogen bond in the heterodimer, asymmetric single-well potentials with a minimum corresponding to (NH4)+(OH2) are obtained for R(NO) distances of less than 2.85 Å. Longer intermolecular separations lead to appearance of a second minimum in the potential (NH3)(OH3)+. The energy barrier between these two minima is much greater for transfer from N to O than for the reverse O to N. Transfer barriers in the two homodimers lie between these two extremes, with interoxygen transfer barriers somewhat higher than for the internitrogen process. Barriers for all systems are found to be sensitive to angular deformations as well as stretches of the H bond. Electronic redistributions occurring at various stages of proton transfer are monitored by means of density difference maps and population analyses. Greater amounts of charge transferred from the proton-accepting molecule to the donor are associated with more facile proton transfers. The calculated energies of the lone pair orbitals of the proton-accepting atom provide another accurate indicator of the height of the barrier to proton transfer. These observations are explained in terms of fundamental principles of electronegativity and orbital interactions.
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o calculation of the vibrational-rotational spectrum of triatomic systems in the close-coupling approach, with KCN and H2Ne as examples
Authors: Tennyson Jonathan , Sutcliffe Brian T.
Published: February 2003

A Hamiltonian for the vibration-rotation motions of atom–diatom systems is derived in body-fixed coordinates and a method for its solution as a close-coupled secular problem is formulated. The radial coordinate is expanded in Morse oscillator functions. Calculations on KCN and H2Ne are presented. For KCN the neglect of Coriolis interactions is found to have little effect. Extensions of the method to problems in more dimensions are suggested.
The dissociation energy of MgO
Authors: Bauschlicher Charles W. , Lengsfield Byron H. , Liu Bowen
Published: February 2003

A b initio CI calculations on MgO(a 3Π) have yielded a best estimate for the dissociation energy of MgO (X 1Σ+) of 2.65±0.16 eV, indicating all available experimental values (3.5–4.3 eV) are too high. The CI calculations, including all single and double replacements from the restricted Hartree–Fock wave functions, were performed using large Slater-type orbital and contracted Gaussian-type orbital basis sets with at least four sets of polarization functions. The best value of the dissociation energy was computed with respect to Mg++O− and then corrected by the experimental electron affinity and ionization potential.
The linked singles and doubles model: An approximate theory of electron correlation based on the coupled-cluster ansatz
Authors: Cullen John M. , Zerner Michael C.
Published: February 2003

From the diagrammatic construction of the full coupled-cluster theory of all single and double excitations, a linearized theory, a direct configuration interaction theory (CISD), a CEPA-like theory, and a linked singles and doubles (LSD) theory are separated. These theories are then compared with one another, with the results from full fourth-order perturbation theory, and with exact results when available. The LSD model, corresponding to the removal of unlinked terms of the CISD, and its spin adapted version, appear most accurate in Pariser–Parr–Pople studies where the exact numbers are known. Examples within the localized bond model are given indicating that this model is also the most successful of those examined in generating not only the basis set correlation, but the necessary delocalization and polarization required to correct for the zeroth-order local description.
Pulse radiolytic studies of the ultraviolet and visible emissions from purified H2O ice
Authors: Quickenden T. I. , Trotman S. M. , Sangster D. F.
Published: February 2003

High purity H2O ice at 88 K was excited by a nanosecond pulsed 0.5 MeV electron beam and was examined for luminescence emission in the wavelength range 200–600 nm. Emission was observed in the three regions 280–300 nm (Gp = 1×10−7 photons/100 eV), 340–460 nm (GP = 2×10−4 photons/100 eV), and 500–600 nm (Gp = 1×10−5 photons/100 eV). No single previous paper has reported emission from all of these three regions in H2O ice. A weak emission band observed at 230 nm by one previous worker was not observed in the present investigation. The overall luminescence yield of (2.4±0.6)×10−4 photons/100 eV lay in between the only two previous estimates of 2×10−3 and 9×10−5 photons/100 eV. Measurements on ice made from water which had been in contact with typical sources of impurity, indicated that impurities were unlikely sources of the luminescence. The luminescence between 310 and 550 nm showed a marked dependence on total accumulated dose, and the dependence conformed to the predictions of a model based on the competitive trapping of a single radiation produced species, by luminescent and nonluminescent reaction centers.
Laser photoionization mass spectroscopy of PbTe, PbSe, and Pb
Authors: Martin T. P.
Published: February 2003

The vapor components of PbTe and PbSe (PbTe, Te2, PbSe, Se2, and Pb) have been ionized by various resonant, multiphoton processes and detected in a mass spectrometer. In this way it is possible to measure the two-photon excitation energies of the molecules in addition to the photodissociation products and their state of excitation. Highly excited Pb atoms formed by the photodissociation of PbSe were resonantly excited to previously unreported, autoionizing, even parity Rydberg levels. The three-photon ionization cross section, containing two-photon resonant excitation, was calculated for PbTe. Inclusion of intermediate vibrational sublevels in the resonant step results in the suppression of certain Franck–Condon peaks.
Determination of lithium ion–rare gas potentials from total cross section measurements
Authors: Polak-Dingels Penny , Rajan Malini S. , Gislason Eric A.
Published: February 2003

Total cross sections have been measured for Li+ ions scattered by He, Ne, Ar, Kr, and Xe in the range EϑR = 5–1000 eV deg. Here E is the laboratory energy of the Li+ beam, and ϑR is the resolution angle of the apparatus. The cross sections have been inverted to obtain accurate estimates of the potential V(R) over a wide range of R including the attractive well region. The results are compared with other theoretical and experimental work on these systems.
Lifetimes and collisions in KH, A 1Σ+, v′ = 5–22
Authors: Giroud Marc , Nedelec Odette
Published: February 2003

KH obtained in a high frequency discharge in K+H2 is selectively excited by a pulsed dye laser to A 1Σ+, v′ = 5–22, J′ = 8 or 9. The radiative lifetimes are measured. They decrease slowly from v′ = 5 (64 ns) to v′ = 19 (53 ns) and rapidly at v′ = 22 (34 ns). Rotational transfer cross sections by collisions with H2 increase from v′ = 5 (41 Å2) to v′ = 19 (92 Å2) as do the electric dipole moments in the levels. The collision with the electrons of the discharge provide rotational transfers where the ΔJ′ = ±1 transitions are the greatest and vibrational transfers Δv′ = ±1, ±2, where the ΔJ′ = 0 transitions are small. These results are to be expected in polar molecules where the interaction of the electron with the permanent dipole moment of the molecule is predominant.
Electron mobility in supercritical propane as a function of density and temperature
Authors: Nishikawa Masaru , Holroyd Richard A.
Published: February 2003

The mobility of electrons (μ) in propane was measured as a function of density (N) at several temperatures above the critical temperature. The quantity μN goes through a minimum at a density just below the critical density and the mobility is quite temperature dependent in this region, as was observed for ethane. Also, μN goes through a maximum above the critical density and becomes quite temperature insensitive at higher densities. The mobility minimum matches a minimum in the velocity of sound in propane and the results at intermediate densities can be accounted for by a Cohen–Lekner equation, utilizing the structure factor S(K). Thus scattering is the result of density fluctuations and a momentum transfer cross section σm of 4 Å2 accounts for the results. At higher densities multiple scattering is important.
Re-entrant isotropic phase of a polypeptide liquid crystal
Authors: Subramanian R. , Wittebort R. J. , DuPré D. B.
Published: February 2003

Optical and C-13 NMR examinations of concentrated solutions of poly-γ-benzyl-L-glutamate (PBLG) in a mixed solvent system containing a denaturant acid, show that this polymer liquid crystal has both a low and high temperature isotropic phase. The latter is due to thermal disruption of long-range orientational order of the elongated macromolecules. The former re-entrant isotropic phase is a result of an intramolecular helix to random coil transition, which leads to a macromolecular conformation inconsistent with liquid crystallinity.
Evidence for high rotational excitation in CO produced by collisions with hot H atoms formed in the photodissociation of HBr
Authors: Wood Carol F. , Flynn George W. , Weston Ralph E.
Published: February 2003

The time dependence of the IR emission profiles is analyzed following photolysis of HBr in the presence of CO. (AIP)
The reaction between oxygen and vinyl radicals
Authors: Donaldson D. J. , Sloan J. J.
Published: February 2003

Vinyl radicals were produced by the Ft C2H3 reaction. An infrared chemiluminescence apparatus was then employed to study the addition of an O atom to a vinyl radical. (AIP)
Direct measurement of a subpicosecond birefringent response in CS2
Authors: Greene B. I. , Farrow R. C.
Published: February 2003

Bifringence in liquid CS2 has been induced by 150 femtosecond laser pulses, and subsequenyly observed to decay. The sample response exhibits both an ultrafast 0.24 ps decay as well as the previously well- characterized 2.16 ps decay. Possible origins of the ultrafast response are discussed with specific reference to a novel coherence effect.
Dependence of inhomogeneous vibrational linewidth broadening on attractive forces from local liquid number densities
Authors: George S. M. , Harris C. B.
Published: February 2003

The dependence of inhomogeneous vibrational linewidth broadening on attractive forces form slowly varying local liquid number densities is examined. The recently developed Schweizer–Chandler theory of vibrational dephasing is used to compute absolute inhomogeneous broadening linewidths. The computed linewidths are compared to measured inhomogeneous broadening linewidths determined using picosecond vibrational dephasing experiments. There is a similarity between correlations of the Schweizer–Chandler and George–Auweter–Harris predicted inhomogeneous broadening linewidths and the measured inhomogeneous broadening linewidths. For the methyl stretches under investigation, this correspondence suggests that the width of the number density distribution in the liquid determines the relative inhomogeneous broadening magnitudes. (AIP)
Far infrared spectrum of α-N2 under pressure
Authors: Medina F. D.
Published: February 2003

Measurements of the infrared spectrum of α-N2 are reported for samples drawn at different points on the melting line. The Grüneisen parameters are calculated from frequency versus temperature plots. (AIP)
Dissociation energy of the InAs molecule
Authors: Piacente V. , Gigli R.
Published: February 2003

A mass spectroscpic investigation is carrier out on the In-As system. The dissocation energy of InAs was derived by measuring he entralpy change of the reaction: InAs→In+1/2AsAd2.
The temperature dependence of the quenching of Mg(3P
J) by H2 and D2: Endoergic chemical reaction as rate limiting
Authors: Breckenridge W. H. , Stewart J.
Published: February 2003

The rate constants for the inefficient quenching of Mg(3s3p 3PJ) by H2 and D2 have been shown to increase sharply with temperature in the 600–800 K range. The quenching rate is controlled by the following endoergic chemical reactions: Mg(3PJ) +H2 → MgH+H, ΔE00=+11.3 kcal/mol, Mg(3PJ)+D2 → MgD+D, ΔE00=+12.8 kcal/mol. A statistical fit of the data to a simple kinetic model shows furthermore that the chemical reactions proceed with no activation barrier beyond the endoergicities, and that E to V, R quenching by H2 and D2 is extremely inefficient. These conclusions are consistent with ab initio calculations of the excited- and ground-state MgH2 potential surfaces. It is also shown that vibrational energy of D2 is not the sole requirement for efficient reaction with Mg(3PJ) and it is proposed that vibrational and translational activation may be comparably efficient for these reactions.
Universal systematic sequences of even-tempered basis functions in electronic structure studies of negative ions
Authors: Cooper David L. , Wilson Stephen
Published: February 2003

Universal systematic sequences of even-tempered basis sets of exponential-type functions are developed for the treatment of negative ions. Calculations are reported for Li−, Be−, B−, C−, N−, O−, and F− within the self-consistent field approximation. Extrapolation procedures are employed to obtain estimates of the basis set limit.
Mo/ller–Plesset treatment of electron correlation effects in (HOHOH)−
Authors: Szcześniak Mal/gorzata M. , Scheiner Steve
Published: February 2003

The effects of electron correlation on the calculated properties of the (HOHOH)− anion are studied using Mo/ller–Plesset (MP) perturbation theory. With this technique, inclusion of corrections up to third order are shown to provide results quite similar to those obtained with an extensive CI approach when equivalent basis sets are used. Barriers to proton transfer between the two oxygen atoms at a fixed R(OO) distance are computed with a number of basis sets ranging from split-valence 4–31G to triple-valence with polarization functions on all atoms, 6–311G**. Each successive enlargement of the basis set leads to a greater barrier. The second-order correction to the energy reduces the Hartree–Fock barrier dramatically while subsequent inclusion of the third-order energy results in an increase over the MP2 barriers. MP3 formalism is found capable of accurately reproducing CI results for both the barrier height and functional dependence of the correlation energy upon the proton position. The potential energy surface is calculated as a function of both the R(OO) distance and the position of the central proton. At the Hartree–Fock level, all basis sets yield a surface with two minima separated by a saddle point, representing the transition state for adiabatic proton transfer. The surface is flattened a great deal by inclusion of second- and third-order corrections such that the barrier to proton transfer is considerably below the estimated zero vibrational level for protonic motion. Electron correlation effects are also responsible for an increase of about 3 kcal/mol in the hydrogen-bond energy of the (HOHOH)− complex.
Ab initio intermolecular potential of the ethylene dimer
Authors: Suzuki Kazunari , Iguchi Kaoru
Published: February 2003

The intermolecular potential of the ethylene dimer in the ground state has been computed nonempirically with the exchange perturbation theory. The principal terms of interaction energy considered are the Coulombic and exchange energies as the first order ones, then the dispersion energy as the second order one, and other higher terms are neglected. Computations were made exactly without multipole expansion approximation, to the order of the square of intermolecular overlap integrals. Nine orientations of molecules are considered. Three kinds of basis set, i.e., STO-3G, 4-31G, and 4-31G* were employed, and the results were compared to each other and also with those by other authors. The potential minimun was obtained for all orientations against results of other authors, and the most stable one has the slightly shifted parallel structure near to that found in the ethylene crystal.
The molecular dynamics simulations of the damping matrices in a Lennard-Jones fluid and testing of the two-relaxation time models for the memory function
Authors: Lee Lloyd L. , Chung Ting-Horng
Published: February 2003

We have carried out the molecular dynamics simulations (MD) for the velocity autocorrelation functions (vacf), the acceleration autocorrelation functions, and the damping matrices in a Lennard-Jones fluid. Seven state conditions, from low densities (ρ*=ρσ3=0.3) to high densities (ρ*=0.85) and from low temperatures (T*=kT/ε=0.73, σ and ε being the Lennard-Jones parameters) to high temperatures (T*=5.2) were investigated. The values of the damping matrices Kn(t=0), n=1,2,3,4, and 5 in the continued fraction representation of the memory kernel, as given by Mori, were obtained directly from the MD via a seventh order backward difference algorithm. These Kn(0) increase rapidly in magnitude as the order increases. They also show strong temperature dependence, but weak density dependence. These damping matrices are used to test the empirical models proposed to represent the memory functions for the velocity autocorrelation. We test some commonly used memory function models with two relaxation times, one representing the short time binary collision effects and the other the long time hydrodynamic effects. It is discovered that in the single dynamic variable autocorrelation approach adopted here none of the empirical models tested perform well in reproducing the MD vacf at intermediate to long times. We attribute this to the lack of mode–mode coupling contributions.
Linear response theory of polypeptide circular dichroism: Bogoliubov exciton theory
Authors: Rabenold David A.
Published: February 2003

A linear response theory of polypeptide circular dichroism is presented. The Bogoliubov collective excitation theory is derived without the use of second quantization techniques and therefore direct insight to the approximations is obtained. The static field at each chromophore is approximated as an external field unaffected by the polarization it induces. Susceptibilities that contain the static field effect are obtained via a Green operator method. These susceptibilities are then used in the geometric expansion of time dependent Hartree theory to obtain the result. Also, a partitioning technique is presented for handling the resulting normal mode problem.
Mode amplitudes in dynamic light scattering by concentrated liquid suspensions of polydisperse hard spheres
Authors: Pusey P. N. , Fijnaut H. M. , Vrij A.
Published: February 2003

This paper concerns the dynamic light scattering by suspensions of polydisperse hard spherical particles. It is concluded that for relatively high volume fractions and fairly narrow distributions, the light scattering correlation function should, to a good degree of approximation, be composed of two independent modes with well-separated decay times. The faster decaying mode describes collective stochastic compression–dilation motions and is present even for a monodisperse system. The slower decaying mode describes the exchange of different species. The relative mode amplitudes are calculated in the Percus–Yevick approximation for hard spheres. The two decay times of fast and slow mode are associated with diffusion coefficients D+ and D−, respectively. In the case of scattering power polydispersity D+ and D− are rigorously identified with collective and self-diffusion, respectively. In the case of size polydispersity D+ and D− can be associated with ‘‘average’’ collective and self-diffusion coefficients. The considerations are limited to zero scattering wave vector and volume fractions above 0.15. Comparison with experimental results from other papers are in favor of the theory.
Zeeman effect of Nd3+ in LaCl3
Authors: Rana R. S. , Kaseta F. W. , Garvey R. H.
Published: February 2003

The Zeeman splittings of many of the energy levels of the 4f3 configuration of Nd3+ in a LaCl3 crystal are measured with the C axis parallel to the magnetic field for a range of field strengths. Zeeman splittings of all the 4f3 configuration energy levels are calculated to first order with and without including J mixing by the magnetic field. Several new levels are identified and many other assignments are confirmed using the experimetnal data and the calculations. Comparison between the experimentally observed splittings and the calculated values is found to be good, in general, although some limitations of the semiempirical wave functions used are discussed.
Photoelectron–photon coincidence studies of halobenzene cations in their excited electronic states
Authors: Maier John P. , Thommen Fritz
Published: February 2003

Fluorescence quantum yields and lifetimes of the cations of 1,3,5-trichloro-, 1,3,5-trichlorotrifluoro, 1,3,5-tribromotrifluoro-, 1,4-dichloro-, and of 1,3-dichlorobenzene in selected levels of their B̃ electronic states have been determined. The principle of these measurements is based on the detection of coincidences between photons and energy analyzed photoelectrons following photoionization. These data, obtained under collision free conditions, yield the radiative and nonradiative rate constants for the cations as a function of their internal energy. With the 1,3,5 derivatives, coincidences were also detected when their cations were generated in higher excited electronic states and the wavelength region of the resulting photons could be located. The implications of these observations on the spectroscopic and relaxation behavior of these cations are discussed.
State selected ion–molecule reactions by a TESICO technique. VI. Vibronic-state dependence of the cross sections in the reactions O+2(X 2Πg, v; a 4Πu, v)+H2→ O2H++H, H+2+O2
Authors: Tanaka Kenichiro , Kato Tatsuhisa , Guyon Paul-Marie , Koyano Inosuke
Published: February 2003

The threshold electron-secondary ion coincidence (TESICO) technique has been utilized to select the vibronic states of the O+2 reactant ions in the endoergic reactions O+2+H2→O2H++H(1) and O+2+H2→H+2+O2(2). The vibronic states selected were X 2Πg, v=19, 20 and a 4Πu, v=0–8, for each of which the relative reaction cross sections have been determined. It has been found that while reaction (1) indeed proceeds with the ground X 2Πg state ions by the vibrational excitation (at collision energies lower than the translational threshold), it is considerably (an order of magnitude) enhanced by the electronic excitation of the reactant ions to a 4Πu. When vibrational energy is added to the a 4Πu state, the cross section of reaction (1) further rises sharply (by a factor of 2) at v=2 and then decreases more slowly, reaching the original (v=0) value at v=4. After that, the cross section apparently decreases by about a factor of 2 at v=8. The cross section of reaction (2) behaves in a manner similar to that of reaction (1) as a function of vibrational quantum number. The magnitudes of the cross sections for both electronic states are, however, consistently smaller than those of reaction (1) by roughly a factor of 10.
‘‘White line’’ in the chlorine K x-ray absorption spectra of K2PdCl4, K2PtCl4, K2PdCl6, and K2PtCl6
Authors: Sugiura Chikara , Ohashi Masanao
Published: February 2003

The chlorine K absorption spectra from complex compounds K2PdCl4, K2PtCl4, K2PdCl6, and K2PtCl6 have been obtained with a 50 cm bent-quartz crystal vacuum spectrograph. An intense ‘‘white line’’ has been found at the absorption threshold and shows the chemical shift which is closely related with the ionization potentials of Pd and Pt, corresponding to the transition from the chlorine 1s level to the lowest unoccupied antibonding orbital originating from the Pd 4d or Pt 5d and Cl 3p orbitals. The other absorption structures are alike throughout four compounds. A tentative explanation for the absorption structures near the K edge is made in terms of the core level-to-empty state transitions in the Cl− ion. Radiation effect is found on the chlorine K absorption spectrum of K2PdCl6.
Molecular beam photoionization study of HgBr2 and HgI2
Authors: Linn S. H. , Tzeng W.-B. , Brom J. M. , Ng C. Y.
Published: February 2003

Photoionization efficiency (PIE) data for HgBr2+ and HgI2+ and their fragment ions have been obtained in the region 600–1350 Å using an oven-type supersonic beam source. The ionization energies (IE) for the X̃ 2Π3/2g states of HgBr2+ and HgI2+ were determined to be 10.560±0.003 and 9.5088±0.0022 eV, respectively. The analyses of the Rydberg series converging to the 2Π1/2g states of HgBr2+ and HgI2+ yield a value of 10.8846±0.0012 eV for the IE of the 2Π1/2g state of HgBr2+ and 10.1953±0.0025 eV for that of HgI2+. The major fragment ions from HgBr2 were identified to be HgBr+, Hg+, Br2+, and Br+ and those from HgI2 were found to be HgI+, I2+, and I+. The measured appearance energies for HgBr+ and HgI+ allow the calculation of the bond dissociation energies for HgBr+ and HgI+ to be 55±2 and 59±1 kcal/mol, respectively. Similar to the observation in the PIE curves for HgCl2+ and its fragment ions, the PIE spectra for HgBr2+, HgI2+, and their fragment ions are dominated by autoionization structures exhibiting asymmetric Beutler–Fano line profiles. The comparison of the PIE curves of HgCl2+, HgBr2+, HgI2+, and Hg+ from Hg confirms the previous conclusion that these autoionizing Rydberg series can be assigned to transitions [(5d)10σg2σu2πu4πg4] → [(5d)9σg2σu2πu4πg4 2D±5/2]np and [(5d)10σg2σu2πu4πg4] → [(5d)9σg2σu2πu4πg4 2D±3/2, ±1/2]np, n≥6, which are mainly associated with the mercury atom in HgX2, X=Cl, Br, and I.
Frequency dependent energetics of a polymer chain represented by the Ising modela)
Authors: López de Haro M.
Published: February 2003

The acoustic analog of the Ising model adapted to dilute polymer solutions is presented. End effects in the case of short chains are explicitly accounted for and shown to become negligible as the length of the chain is increased. Qualitative agreement with the experimental observations is obtained which allows us to interpret the ultrasonic relaxations in dilute polymer solutions as arising from cooperative motion.
CS(a3πr) chemiluminescence from the reaction C+OCS at 300 K
Authors: Dorthe G. , Caille J. , Burdenski S.
Published: February 2003

The reaction C+OCS is proposed as a new candidate for an electronic transition chemical laser. A strong chemilumenescence is observed from CS* between 340 and 390 nm. The characteristic of this emission is futher discussed. (AIP)
Role of d functions in ab initio calculation of the equilibrium structure of H2S–HF
Authors: Scheiner Steve
Published: February 2003

Full geometry optimizations are performed to determine the equilibrium geometry of the hydrogen-bonded complex H2S–HF. The angle between the plane of the H2S moiety and the H-bond axis calculated with the 4–31 G basis set is 106° as compared to the experimental value of 91±5°. This quantity is reduced significantly when d orbitals are added to the basis set, yielding an angle within experimental error of 91°. (AIP)
A statistical interpretation of the rotational temperature of NO desorbed from Ru(001)
Authors: Bialkowski Stephen E.
Published: February 2003

A simple model of the rotational state of NO prior to thermal desorption from Ru(001) surface is developed in terms of the rotational heat capacity. The predicted rotational temperature of the desorbed species is consistent with known data on this system. The model is extended to predict translational energy anisotropy in the desorbed NO.
Response to ‘Highly excited states of HCN: The probable applicability of classical dynamics’
Authors: Lehmann K. K. , Scherer G. J. , Klemperer W.
Published: February 2003

The comments of Farrelly and Reinhard on a previous publication1 of the authors are answered. The applicability of classical mechanics to the problem of excited state of HCN is further discussed. (AIP)
Singlet exciton transport in substitutionally disordered naphthalene crystals: Percolation and generalized diffusion
Authors: Gentry Stuart T. , Kopelman Raoul
Published: February 2003

Experimental data is presented for singlet exciton transport in a ternary naphthalene system (C10H8/C10D8/BMN). The trapping probability varies with guest concentration and with temperature. The data at 4.2 K are consistent with a generalized diffusion treatment such as that proposed by Gochanour, Andersen, and Fayer. The 1.8 K data conform to a quasistatic percolation model. The supertrap induced energy funnels which might affect this energy transport are limited to nearest neighbors. The BMN fluorescence spectra are affected by exciton–phonon interactions similar to Herzberg–Teller coupling.
An EPR study of rare-earth impurities in single crystals of the zircon-structure orthophosphates ScPO4, YPO4, and LuPO4 a)
Authors: Abraham M. M. , Boatner L. A. , Ramey J. O. , Rappaz M.
Published: February 2003

Ceramic materials based on the lanthanide orthophosphate series of compounds are known to be highly stable both chemically and physically. These characteristics have recently led to an extensive evaluation of these substances as potential primary containment media for the disposal of high-level radioactive wastes. Since one important class of high-level nuclear waste (i.e., reprocessed light water reactor spent fuel) contains a relatively high concentration of various lanthanides, the solid state chemical properties of the mixed rare-earth and actinide-doped orthophosphates are of considerable practical interest. The Kramers’ ions Ce3+, Nd3+, Dy3+, Er3+, Yb3+, and U3+ have been incorporated in single crystals of the tetragonal symmetry hosts ScPO4, YPO4, and LuPO4, and EPR spectroscopy has been used to verify the substitutional behavior of these ions and to investigate their electronic ground state properties. Principal axial spectroscopic splitting factors and hyperfine parameters were determined. These results are compared to those obtained for the same paramagnetic ions in other hosts characterized by crystal fields with tetragonal symmetry at the impurity-ion site.
Weierstrassian Levy flights and self-avoiding random walks
Authors: Shlesinger Michael F.
Published: February 2003

An analogy, involving space–time relationships, is made between a self-avoiding random walk and a Weierstrass random walk. The self-avoiding random walk is non-Markovian while the Weierstrass random walk is Markovian, but with a built-in self-similarity characterized by a fractal dimension. It is proposed that the self-avoiding random walk can be viewed as a Weierstrass random walk whose trajectory is composed of maximally packed self-similar clusters with the symmetry of the underlying lattice.
Dependence of ion cyclotron frequency on electric field inhomogeneity
Authors: Hartmann H. , Chung K.-M. , Baykut G. , Wanczek K.-P.
Published: February 2003

A quantum mechanical treatment of classically behaving ion motion in an ICR drift cell is given. For this description the coherent state wave function, as wave packet, minimized according to the uncertainty principle has been applied. The electric field inhomogeneity effect upon the cyclotron frequency is determined with the Schrödinger perturbation theory. The theoretical results are compared with experimental determinations of the dependence of the cyclotron frequency on the magnetic field and found to be in good agreement. They can be utilized for calibration of the mass scale.
Shear viscosity measurements near a multicomponent fluid tricritical point
Authors: Izumi Yoshinobu , Miyake Yasuhiro
Published: February 2003

Shear viscosity measurements have been performed near the tricritical point of an ethanol– water–benzene–ammonium sulfate mixture. A weak divergence was obtained in the range of 7×10−4<(T−Tt*) /Tt*<10−2, where Tt* is a tricritical spinodal temperature. The results are compared with the existing theories.
Microwave spectrum, torsional barrier, and structure of BH3NH3
Authors: Thorne L. R. , Suenram R. D. , Lovas F. J.
Published: February 2003

The microwave spectra of nine isotopic species of borane monoammoniate (11BH3NH3, 10BH3NH3, 11BH3ND3, 10BH3ND3, 11BD3NH3, 11BH3 15NH3, 10BH3 15NH3, 11BD2HNH3, 11BH3ND2H) have been observed. The rotational constants, centrifugal distortion constants, dipole moment, torsional barrier, and molecular geometry of borane monoammoniate were determined from these spectra. The rs structure is: BN=1.6576(16) Å, BH=1.2160(17) Å, NH=1.0140(20) Å, ∠NBH=104.69(11), ∠BNH=110.28(14). The dipole moment is 5.216(17) D. The torsional barrier about the B–N bond, V3, is 2.047(9) kcal mol−1 for 11BH3ND2H and 2.008(4) kcal mol−1 for 11BD2HNH3.
Laser vaporization of alloys: Laser induced fluorescence of heteronuclear metal clusters
Authors: Bondybey V. E. , Schwartz G. P. , English J. H.
Published: February 2003

We demonstrate in this manuscript that the laser vaporization–laser induced fluorescence technique can be a very useful tool in studies of heteronuclear metal molecules. We examine here the products of vaporization of copper with the group III A elements Ga and In. The electronic transitions of CuGa and CuIn diatomics are reported and discussed, as well as some new observations of the Cu2 spectra and dynamics. It is also shown that the metals are initially vaporized in an atomic form and that the molecular species are formed collisionally in the gas phase.
Scaling relations for inelastic collision data obtained from the initial value representation (IVR)
Authors: Augustin Stuart D.
Published: February 2003

In this paper we have developed scaling relations for inelastic collision data based upon the IVR, an approximation which is accurate in both the sudden and adiabatic limits. We have used this to obtain connections between S-matrix elements at either the same kinetic energy or the same total energy. The constant kinetic energy scaling has the same overall form as the earlier energy corrected sudden (ECS) theory, but with different adiabaticity factors. In a practical application these factors may be obtained from a knowledge of the scattering potential or else from model collision lifetime functions, examples of which are presented in this work. The IVR scaling theory reduces the importance of multiquanta transitions relative to the ECS result, and it also provides an adiabatic correction to the phases of the S-matrix elements. Numerical calculations for a collinear oscillator problem are given as a test of the total energy scaling relations.
Mutual neutralization and chemi-ionization collisions of lithium and fluorine
Authors: Bienstock S. , Dalgarno A.
Published: February 2003

Calculations are reported of the cross sections and rate coefficients for the mutual neutralization of Li+ and F− ions and for chemi-ionization in collisions of neutral Li and F atoms. A quantal two-state diabatic formulation is used. It is pointed out that because of the Coulomb attraction in the product channel, chemi-ionization cross sections are finite at threshold.
Electron diffraction studies of supersonic jets. I. Apparatus and methods
Authors: Bartell Lawrence S. , Heenan Richard K. , Nagashima Makoto
Published: February 2003

We describe the apparatus and methods used to obtain electron diffraction patterns of low-temperature species produced from molecules seeded into supersonic expansions of helium or neon carrier gases. Although systems designed for molecular beam or spectroscopic studies are unsuitable for electron diffraction, alternative arrangements were found that give diffraction patterns of good quality. Characteristics of gas jets issuing from different nozzle designs are discussed. Procedures are outlined for separating the desired signal from considerable background scattering by the carrier gas and to correct for broad gas density profiles in analyses of diffraction data.
Absorption spectra of dimer negative ions
Authors: Carmichael Ian , Funabashi Koichi
Published: February 2003

The absorption spectra of dimer negative ions have been studied as a function of vibronic (‘‘electron-phonon’’) coupling strength and electron tunneling (‘‘transfer integral’’) parameter. A model Hamiltonian for the dimer system has been taken from that of Fulton and Gouterman and the eigenvalue equation has been solved by the Merrifield method. As the vibronic coupling strength is increased for a fixed value of tunneling parameter, the physical meaning of the absorption spectrum changes from that of an electronic resonance transition to that of a vibronic electron transfer transition.
Electron diffraction studies of supersonic jets. II. Formation of benzene clusters
Authors: Heenan Richard K. , Valente Edward J. , Bartell Lawrence S.
Published: February 2003

Expansions of benzene at 1–10 mol % in neon or helium with various nozzle types have produced clusters of benzene molecules. Preliminary comparisons with intensities from the bulk liquid and with model calculations based on solid state crystal structures suggest that on the average the clusters are probably considerably larger than a 13 molecule unit, and have a vibrational temperature on the order of 100–150 K. Unlike clusters of spherical or quasispherical molecules previously found to pack in nearly crystalline arrays, benzene molecules appear to be unable to organize into regular arrays in the time of our experiments. Local order in clusters is similar but not identical to that in the solid, resembling that expected for a supercooled liquid. The present approach, exploiting several advantages of electron diffraction over alternative methods, shows promise as a new means of studying liquids or glasses.
Mode specificity in the unimolecular dissociation of formaldehyde (H2CO→H2+CO), a two-mode model
Authors: Waite B. A. , Gray S. K. , Miller W. H.
Published: February 2003

The reaction path (the minimum energy path in mass-weighted Cartesian coordinates) and all the coupling functions which fully characterize the reaction path Hamiltonian of Miller, Handy, and Adams [J. Chem. Phys. 72, 99 (1980)], have been calculated for the unimolecular dissociation of formaldehyde (H2CO→H2+CO) in its ground electronic state. The reaction coordinate and the four other in-plane vibrational modes are strongly coupled to each other, but the out-of-plane vibration is coupled directly only to the reaction coordinate. Calculations of the type of Waite and Miller [J. Chem. Phys. 73, 3713 (1980); 74, 3910 (1981)] for the state-specific unimolecular rate constants are carried out for a two-mode model consisting of the reaction coordinate and the out-of-plane vibration, and one observes a significant degree of mode specificity; i.e., the unimolecular rate constant for a given metastable state is not a smooth function of the energy of the state. It is suggested that this mode specificity may persist in the complete six-mode system.
Energy partitioning in the 532 nm photofragmentation of nitrosyl cyanide (NCNO)
Authors: Pfab J. , Häger J. , Krieger W.
Published: February 2003

The 532 nm photodissociation of gaseous NCNO has been studied by a tandem pulse technique utilizing repetitive nanosecond laser pulses for dissociation and for delayed, time-correlated laser-induced fluorescence probing. Dissociation occurs within less than 3 ns, and both CN(X) and NO(X) have been identified as primary fragments. The central portions of their rotational distributions correspond to Boltzmann distributions with temperatures of (1010±50) K for CN and (930±50) K for NO. Parent rotation and angular momentum from bending vibrations of the Ã state levels populated at 532 nm account for the observed fragment rotation. Little angular momentum is partitioned into orbital motion of the fragments indicating that the molecule dissociates from a linear or quasilinear nuclear configuration. The observed distribution of the 9300 cm−1 of available energy into internal and relative translational degrees of freedom of the fragments is consistent with predissociation of bound Ã state levels into the continuum of ground state NCNO.
On the dissociation energy of ArCO+2
Authors: Pratt S. T. , Dehmer P. M.
Published: February 2003

Bond dissociation energy of ArCO+2 is determined by using photoionization mass spectroscopy. The result is compared with the bond dissociation energies of the rare gas dimer ions and the (CO2)2+ ion. (AIP)
Distribution of internal energy in NO vibrationally excited by a hot platinum surface
Authors: Mantell D. A. , Maa Y.-F. , Ryali S. B. , Haller G. L. , Fenn J. B.
Published: February 2003

The rotational, vibrational and electronic spin orbit energy distributions are measured for NO molecules colliding with a hot platinum foil. (AIP)