bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation of magnetic resonance data from water nuclei in heterogeneous systems
Authors: Halle Bertil , Wennerström Håkan
Published: February 2003

Nuclear magnetic resonance (NMR) data from water nuclei (1H, 2H, and 17O) can provide much information about the state of water in heterogeneous systems. In the present work, we present a theoretical framework for the interpretation of such data and discuss the implications of the theory. Due to the local anisotropy in heterogeneous systems, it is necessary to consider two components of water motion: a fast anisotropic reorientation superposed on a more extensive slow motion. On the basis of the experimentally verified assumption that these motions occur on different time scales, we develop a ’’two-step’’ model of relaxation, showing that both motions may give important contributions to the relaxation. We derive a simple expression for the relevant correlation function, valid for isotropic systems. Anisotropic systems are also treated, making use of a new symmetry theorem for time correlation functions. The proof of this theorem is given in an Appendix. The magnitudes of the water 2H and 17O quadrupole coupling constants are estimated to 0.222 and 6.67 MHz, respectively. Results of ab initio quantum chemical calculations are presented, demonstrating the insensitivity of the water 17O field gradient to nearby ionic species. The possibilities and limitations of the NMR technique in answering the fundamental questions about water structure and dynamics in heterogeneous systems are discussed. We suggest a novel interpretation of the well-known invariance of the ratio of 1H and 2H splittings. Furthermore, we argue that the available NMR data are consistent with a short-ranged (≲2 molecular layers) perturbation of the water tumbling rate and anisotropy.
Another look at the EPR of Cr3+ in (NH4)x Tl1−xAl(SO4)2⋅12H2O
Authors: Garrett B. B. , Bopp J. M.
Published: February 2003

Mixed crystal alums were prepared by evaporation of aqueous solutions of the component alums with added chromic sulfate. An EPR study of Cr3+ was made, and after that these samples were analyzed for thallium, aluminum, and chromium by atomic emission and absorption.(AIP)
Note on ionization potentials in the Thomas–Fermi theory
Authors: Kemister Gary , Nordholm Sture
Published: February 2003

Modifications of the Thomas-Fermi theory are considered for the calculation of ionization potentials in atoms. It is contended that errors can be minimized by the use of an inverse Koopmans method which yields much improved ionization potentials.(AIP)
The crystal structure of the noble gases
Authors: Borden Brett , Radin Charles
Published: February 2003

We show that consideration of surface energies is sufficient to explain the tendency of the heavier noble gases to crystalize in a face centered cubic lattice rather than the expected hexagonal close packed structure.
Molecular beam photoionization study of SO2 and (SO2)2
Authors: Erickson J. , Ng C. Y.
Published: February 2003

Photoionization efficiency (PIE) data for SO2+ have been obtained with a wavelength resolution of 0.14 Å (FWHM) in the region 625–1005 Å using the molecular beam method. The ionization energy (IE) of SO2 was determined to be 12.348±0.002 eV (1004.08±0.20 Å). Similar to the observation in the PIE curve for O3+, the spacing for steplike structure observed near the threshold was found to be irregular. Weak structures which arise by autoionization from different vibrational states of Rydberg levels were also resolved in this region. The analysis gives average vibrational spacing of 386, 428, 716, 745, 911, 938, and 956 cm−1 for these Rydberg states. The appearance energy (AE) for the photodissociative ionization processes SO2+hν→SO++O+e− and S++O2+e− were measured to be 15.953±0.010 eV (777.2±0.5 Å) and 16.228±0.030 eV (764±1.5 Å), respectively. Using the AE for the formation of SO+ from SO2, and the heats of formation of SO2, SO, and O, the IE of SO is deduced to be 10.28±0.02 eV. This value is in excellent agreement with that reported previously by Dyke et al. From the observed IE (11.72±0.03 eV) of (SO2)2, the IE of SO2, and the estimated binding energy (0.03 eV) of (SO2)2, the bond dissociation energy of SO2+ ⋅ SO2 is found to be 0.66±0.04 eV. Using the measured AE (15.38±0.06 eV) for S2O3+ production from (SO2)2, a lower bound for the binding energy of SO+ ⋅ SO2 was calculated to be 0.60 eV.
Third body effects on reactions in liquids
Authors: Bose S. , Medina-Noyola M. , Ortoleva P.
Published: February 2003

A hard sphere model of chemical reaction is extended to allow for both a change of mass and smooth tail potential upon reaction as well as the dependence of the threshold for reaction on the proximity of other bodies. With this extended model we study the slow reaction limit for condensed media and obtain generalized rate coefficients which may show marked deviation from Enskog behavior when the activation barrier height depends strongly on the presence of other particles. A variety of solvent and homogeneous catalysis or inhibition and ionic strength effects are studied.
Low energy crossed beam study of the reaction H+2+Ne→HNe++H
Authors: Bilotta R. M. , Farrar J. M.
Published: February 2003

We present a study of the title reaction over the relative translational energy range 0.87 to 4.05 eV. At all collision energies the products are formed with translational energy significantly in excess of the predictions of the spectator stripping model. Experiments performed with differing values of the reagent mean vibrational energy suggest that the high lying vibrational states of H+2 preferentially yield highly internally excited HNe+ products. We discuss the role of a gradual approach to the potential surface barrier as a mechanism for yielding highly translationally excited HNe+ products.
Quasiclassical trajectory studies of the H+H2 reaction on an accurate potential-energy surface. III. Comparison of rate constants and cross sections with experiment
Authors: Mayne Howard R. , Toennies J. Peter
Published: February 2003

Quasiclassical trajectories computed for the H+H2 reaction on the accurate Siegbahn–Liu–Truhlar–Horowitz potential-energy surface are presented. Reaction rate constants as a function of temperature for H2 in the ground and first excited vibrational state are compared with experimental rate data. For v = 0, agreement is found to be excellent for all isotopic combinations. For v = 1, however, all theoretical results predict much smaller rate constants than are observed experimentally. This discrepancy cannot be ascribed to the absence of tunneling inherent in classical mechanics and is unlikely to be due to errors in the surface. Angular distributions in the laboratory frame have been computed from theoretical results for D+H2 and H+T2 and compared with recent experiments. Agreement is fairly good.
A site distribution study of dilute 119Sb and 119mTe on solidification of SnTe and SnSb by Mössbauer emission spectroscopy of 119Sn
Authors: Ambe F. , Ambe S.
Published: February 2003

Mössbauer emission spectroscopy of 119Sn was applied to the study of site distribution of carrier-free 119Sb and 119mTe on crystallization of SnTe and SnSb melts, respectively. 119Sb was incorporated into both the Sn and Te sites of SnTe, the distribution ratio depending on the stoichiometry of the matrix. 119mTe was found exclusively in the Sb site of SnSb.(AIP)
Total differential scattering cross sections for ArHCl
Authors: Buck U. , Schleusener J.
Published: February 2003

The total differential cross sections for AlHC1 are measured. A coupled state calculation was performed to find a potential surface to reproduce the measured data.(AIP)
Comparison of silver atom solvation in glassy and polycrystalline ices
Authors: Ichikawa Tsuneki , Li Anson S. W. , Kevan Larry
Published: February 2003

Electron spin echo studies have been carried out for Ag0 in a 9 M sodium perchlorate aqueous glassy matrix at 4.2 K. The analysis of the nuclear modulation patterns shows that the hydration structure of Ag0 initially formed at 4.2 K is the same as that in polycrystalline ice. In contrast to polycrystalline ice, no change in the solvation structure takes place upon warming the sample to 77 K. The solvation process via OH bond rotation in polycrystalline ice is suggested to occur via defects in the ice structure adjacent to Ag0 in addition to hydrogen bonding interactions. (AIP)
A numerical multiconfiguration self-consistent-field method for diatomic molecules
Authors: Adamowicz Ludwik , McCullough E. A.
Published: February 2003

A numerical solution of the multiconfiguration self-consistent field problem for the diatomic molecule is presented. The solution is based on a partial-wave expansion of the orbitals in protate spherical coordinates. (AIP)
Comment on the ground state of iron (III) in the mixed crystal system Fe[S2CN(C2H5)2]2ClxBr1−x
Authors: Kostikas A. , Wickman H. H.
Published: February 2003

Mössbauer data for the pure Fe[S2CN(C2H5)2]2Br and the solid solution Fe[S2CN(C2H5)2]2dxBr1−x are analyzed. The ground state magnetic properties of iron III are discussed. (AIP)
The complete wave equation of a nonlinear polyatomic molecule
Authors: Webster Frank , Huang Ming-Ju , Wolfsberg Max
Published: February 2003

The complete nonrelativistic wave equation of a nonlinear polyatomic molecule, including the electronic motion, is formulated in molecule fixed coordinates. The method is an extension of that used by Pickett to obtain the molecular rotation–vibration wave equation. Both the choice of rotating axes and the choice of internal vibrational coordinates are general. The transformation to quantum mechanics is undertaken after the rotating axes and the vibrational coordinates have been introduced. The total molecular wave function, after elimination of the motion of the center of mass, is written as a sum of products of eignfunctions of the rigid symmetric top Hamiltonian and of functions of the internal molecular (vibrational and electronic) coordinates. The coupled wave equations for the functions of internal coordinates are derived. Application is made to a nonlinear triatomic molecule and the result is compared with a previous formulation. By contrast to the present formulation, the transformation to quantum mechanics in the previous formulation had been carried out for the Hamiltonian in space fixed coordinates.
Application of the Onsager model to the theory of the dielectric constant of nonpolar liquids
Authors: Bokov O. G. , Naberukhin Yu. I.
Published: February 2003

In the Onsager model on the basis of statistical calculation of the cavity radius by the method proposed by Linder and Hoernschemeyer using experimental data for the radial distribution function g(r) in liquids, the molecular polarizability changes Δα under phase transition from gaseous to liquid state are evaluated for eight substances: noble gases, CH4, CF4, and water. For all liquids with the exception, perhaps, of helium and neon (everything depends on the accuracy of the experimental data for the dielectric constant ε and the polarizability α0 of noninteracting molecules in gases) Δα proves to be positive. Contributions of dipole and overlap effects to Δα in liquid He, Ne, and Ar are discussed on the basis of the approximate calculation of the dipole part using Slater one-electron orbitals and theoretical results for the two-body contribution to electron overlap. The Onsager model allows one to calculate also the Kirkwood fluctuation correction to the Clausius–Mossotti function and values of some three-body integrals.
The interaction of helium with α-quartz
Authors: Kunc Joseph A. , Shemansky D. E.
Published: February 2003

A detailed method of calculating the three-dimensional interaction of gas atoms with solid surfaces has been developed in order to provide a quantitiative means of determining atmospheric evolution and global distribution on exospheric planetary bodies. The computational method involves accurate structural models of the surface and subsurface, and numerical solution of 60-dimensional differential equations of motion in a Monte Carlo calculation of the collision process. Preliminary results for the He–α-quartz system are described.
Electron–nuclear double resonance on copper (II) tetraimidazole
Authors: Van Camp Harlan L. , Sands Richard H. , Fee James A.
Published: February 2003

We have investigated the electron–nuclear double resonance (ENDOR) from frozen aqueous solutions of 65Cu++(imidazole)4, 65Cu++ (imidazole–15N)4, and 65Cu++(imidazole–Dn)4, where n = 1, 2, 3, and 4 for selectively deuterated imidazole. We have observed ENDOR associated with the imidazole protons and the two imidazole nitrogens. The selective deuteration has allowed us to attempt identification of the weakly coupled protons responsible for the ENDOR spectrum, and a comparison of the overall line shape of that spectrum taken at two extreme points of the EPR spectrum suggests that some of the imidazole planes are tilted with respect to the plane of the complex. The ENDOR arising from the nitrogen nearest the copper is primarily isotropic with A(g⊥) = 41.6±1.5 MHz and A(g∥) = 39.8±1.5 MHz. The resonance shows little structure and seems consistent with a picture that requires some inequivalence among the various imidazoles. The remote nitrogen ENDOR reveals both hyperfine and quadrupole effects with approximately isotropic A(14N) = 1.79 MHz, Qz′z′?0.360 MHz, and Qx′x′y′x′?0.349 MHz. These values are in agreement with the results of the nuclear modulation effect [J. Chem. Phys. 69, 4921 (1978)]. The values for the quadrupole constants are thought to be accurate within 10% and are the same as are found in free imidazole. It is also demonstrated that, in this instance, ENDOR and the nuclear modulation effect are complementary in that they have each provided different parts of the same hyperfine spectrum.
The rotational spectrum, structure, and molecular properties of the ethylene–HCl dimer
Authors: Aldrich P. D. , Legon A. C. , Flygare W. H.
Published: February 2003

Three isotopic species of a hydrogen bonded dimer formed between ethylene and HCl have been observed through assignment of their rotational spectra using a pulsed, Fourier transform microwave spectrometer in which a gas mixture is pulsed into an evacuated Fabry–Perot cavity. The spectra unambiguously reveal a nonplanar, near prolate, asymmetric top (κ = −0.9880) in its ground vibrational state. The equilibrium structure has C2V symmetry with the HCl on the C2 symmetry axis of the dimer, perpendicular to the carbon–carbon bonding axis with the hydrogen atom located between the chlorine and the ethylene molecule, pointing midway between the carbon atoms. The chlorine atom is situated, on average, 3.724 Å from the edge of the ethylene molecule. The following spectroscopic constants have been obtained for the ethylene–H35Cl dimer: the rotational constants are A = 25 457(349), B = 2308.143(3), and C = 2167.970(3) in units of MHz; the chlorine nucleus quadrupole coupling constants are χaa = −54.076(4), χbb = 27.091(6), and χcc = 26.985(10) in units of MHz, and the centrifugal distortion constants are DJ = 7.2(2) and DJK = 282(5) in units of kHz.
An ENDOR study of alkali metal–fluorenone biradicals randomly oriented in a rigid matrix
Authors: van Willigen Hans , Mulks Charles F.
Published: February 2003

An ENDOR study has been made of alkali metal–fluorenone biradicals (M+F−)2 randomly oriented in a rigid matrix. By an appropriate selection of the magnetic field settings in the ESR spectrum, ENDOR signals are obtained that convey information on signs and magnitudes of hyperfine splittings along specific axes in the dimer. The ENDOR spectra also give information on the 23Na quadrupole tensor components in (Na+F−)2. The information gives an insight into the structure of the dimers.
Effects of eccentricity on nuclear magnetic relaxation by intermolecular dipole–dipole interactions: 13C relaxation of neopentane
Authors: Albrand J. P. , Taieb M. C. , Fries P. , Belorizky E.
Published: February 2003

In order to study the eccentricity effects on the nuclear magnetic relaxation by intermolecular dipole–dipole interactions, we measured the relaxation times T1 of the center and off-center 13C nuclei in neopentane C(CH3)4. To eliminate a competition between several relaxation machanisms, mainly with the protons, di-t-butylnitroxide free radicals were included with concentrations varying up to 5.6×1020 paramagnetic centers × cm−3. Under these conditions, the dominant relaxation mechanism for the resonating 13C nuclei spins arises from their interactions with the electronic spins of the free radicals. A difference of 15% between the relaxation times of the central 13C and of the off-center carbons is observed. These results are partially interpreted by using the spectral densities j2(ω) resulting from translational and rotational motions as established in our previous work. It is shown that pair correlation effects must also be taken into account to improve the fit with the experimental data.
Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes
Authors: Kuznetsov A. M. , Ulstrup J.
Published: February 2003

Intramolecular electron transfer (ET) over distances up to about 10 Å between states in which the electron is localized on donor and acceptor groups by interaction with molecular or external solvent nuclear motion occurs, in particular, in two classes of systems. The excess electron in anionic radicals containing two aromatic end groups connected by a flexible polymethylene chain or a rigid cyclohexane frame is thus trapped on either aromatic end group, and ET between these groups can be detected by ESR techniques. Intramolecular ET also occurs in binuclear transition metal complexes in which the coupling between the metal centers [(Ru(II)/Ru(III) and Ru(II)/Co(III) couples] is sufficiently weak (class I or II mixed valence compounds). The ET mechanism can involve either direct transfer between the donor and acceptor groups or a higher order mechanism in which ET proceeds through intermediate states corresponding to the localization of the electron on the interconnecting fragments. We have derived rate expressions for the different conceivable intramolecular ET pathways. In particular, we have incorporated the nuclear motion not only in the initial and final states but also in the intermediate states. We have furthermore provided criteria for the distinction between direct ET, ET through high-energy (superexchange), and low-energy (’’radical’’ intermediate mechanism) intermediate states on the basis of experimental rate data and illustrated this with data for organic radical anions, and for intramolecular and inner sphere ET for transition metal complexes.
IOSA investigations of the effects of potential surface topography upon elastic and inelastic scattering and rotational relaxation in the (He, CO2) system
Authors: Agrawal P. M. , Raff L. M.
Published: February 2003

The effect of potential surface topography upon elastic and inelastic scattering has been investigated using the infinite-order sudden approximation (IOSA) to compute total differential and integral cross sections, state-to-state cross sections, and the relaxation rates of depleted levels in the (He, CO2) and (3He, CO2) rigid rotor systems on six different potential energy surfaces that include three surfaces obtained from electrom–gas type calculations, two ab initio SCF surfaces, and one surface (KPK) obtained by empirical fitting to the measured total differential cross section. It is found that the total elastic, inelastic, and differential cross sections are very sensitive to the long-range attractive terms in the potential, and the differential cross sections are also found to be significantly dependent upon the topography of the repulsive regions of the surface. Consequently, differential cross sections are very sensitive probes of surface topography and should be the data of choice for purpose of empirical adjustment of a surface. In contrast, the relaxation rates of a depleted rotational level are found to be insensitive to the details of the surface. In addition, the relaxation rate and total inelastic cross section out of state j are found to be almost independent of the particular j state involved. Consideration of the microscopic details leading to these results suggests that similar behavior will be observed in other systems that are nearly classical with closely spaced energy levels. Of the surfaces investigated, the KPK surface gives results that are in closest agreement with experiment. The electron–gas and SCF surfaces, when augmented by a van der Waals attractive term, give similar results which are almost as good as those obtained on the empirically adjusted KPK surface. This suggests that a reasonable surface for a closed-shell system can be obtained by either procedure. The IOSA results for the relaxation rates and total inelastic cross sections are found to be in excellent agreement with quasiclassical trajectory calculations. However, the degree of agreement for quantities associated with state-to-state transitions is reduced.
Inelastic scattering of He atoms from Cu(001) at low temperature with energy analysis
Authors: Mason B. F. , Williams B. R.
Published: February 2003

A LiF crystal analyzer has been used to measure phonon creation events when a low energy He beam scatters from a Cu(001) surface at low temperature (16 °K). As only phonon creation events were observed, the inelastic scattering was subspecular. Atom parallel momentum gain and loss events were observed and both bulk and surface modes contributed to the inelastic scattering. An elastic component of scattering was observed over a wide angular range.
Floquet theory and complex quasivibrational energy formalism for intense field molecular photodissociation
Authors: Chu Shih-I
Published: February 2003

A practical and nonperturbative method is presented for studying molecular photodissociation processes in the presence of (weak or intense) electromagnetic fields, using only square-integrable (L2) functions. By means of the complex coordinate transformation and L2 discretization of the vibrational continua, the complex quasivibrational energies (QVE) of the Floquet Hamiltonian can be determined by standard non-Hermitian eigenvalue analysis. The real parts of the QVE’s provide the ac Stark-shifted vibronic energies, whereas the imaginary parts are related to the photodissociation transition rates. The theory is applied to the direct photodissociation of H+2(1sσg–2pσu) in both weak and strong fields.
Time-resolved infrared study of bimolecular reactions between t
e
r
t-butyl radicals
Authors: Bethune D. S. , Lankard J. R. , Sorokin P. P. , Schell-Sorokin A. J. , Plecenik R. M. , Avouris Ph.
Published: February 2003

The gas phase IR spectrum of t-butyl radicals near ∼3μm has been observed by the time-resolved infrared technique known as TRISP. The transient spectrum is observed to decay with second-order kinetics, and a total rate of decay kc+kd = 1010.26 liter mole−1 sec−1 is measured. From a gas chromatograph/mass spectrometer analysis of the reaction products, it is found that kd/kc = 2.9. Thus kc = 109.67 and kd = 1010.13 liter mole−1 sec−1. The t-butyl radicals were created by ruby laser photolysis of monomeric (CH3)3CNO vapor.
Kinetic isotope effect in the heterogeneous reaction of graphite with H2O (D2O)
Authors: Yates John T. , McKee D. W.
Published: February 2003

Thermogravimetric studies have been carried out for the reaction of H2O (D2O) with pure graphite surfaces and with graphite surfaces containing BaCO3 catalyst. At temperatures near 1200 K the kinetic isotope effect has been measured to be about a factor of 2 for both pure graphite and BaCO3–graphite. This value of the ratio of rates for H2O compared to D2O is consistent with zero point energy differences between the two isotopic reactants, and suggests that the transition state in the rate determining step involves a complex in which an O–H bond is being broken. The similarity of the magnitude of the isotope effect for both the catalyzed and the uncatalyzed reaction suggests that in both cases a similar O–H bond breaking mechanism is operative in the rate determining step.
Reaction of ethanol and CH3CH(OH) radicals with atomic and molecular oxygen
Authors: Washida Nobuaki
Published: February 2003

The reaction of oxygen atoms with ethanol in a fast flow system was studied with a photoionization mass spectrometer. A radical formed from O+C2H5OH was photoionized by the Xe lamp and identified as the alpha-ethanol radical, CH3CH(OH), i.e., CH3CD(OH) (m/e = 46) and CD3CD(OH) (m/e = 49) were observed in reactions of O+CH3CD2OH and C2D5OH, respectively. The major primary product in the subsequent reaction of alpha-ethanol radicals with atomic oxygen was found to be acetaldehyde (79%±8%) and no formation of vinyl alcohol was observed, i.e., CH3CDO (m/e = 45) and CD3CDO (m/e = 48) were observed in reactions of O+CH3CD2OH and C2D5OH, respectively: O(3P)+CH3CH(OH)→CH3CHO+OH (4a). The reaction of 18O(3P)+C2D5OH produced only CD3CDO (m/e = 48). This fact shows that acetaldehyde is produced by the hydrogen abstraction reaction by O(3P) from the O–H in the alpha-ethanol radical. The competition experiment among O(3P) and O2 for the alpha-ethanol radical shows that alpha-ethanol radicals react (0.14±0.04) times more slowly with molecular oxygen than with atomic oxygen. This result suggests that the reaction of alpha-ethanol radicals with molecular oxygen is very rapid, and that the reaction probably proceeds by a two body reaction to form acetaldehyde and HO2.
Electron diffraction studies of laser-pumped molecules. II. Collisionally assisted absorption by SF6
Authors: Bartell L. S. , Kacner M. A. , Goates S. R.
Published: February 2003

Supersonic microjets of SF6 were pumped with the cw output of a CO2 laser. Power densities ranged from 2–4 kW/cm2 at the nozzle exit (P?200 Torr) to 25 kW/cm2 downstream. Amplitudes of molecular vibration were found to increase significantly when the laser was tuned to the ν3 resonance and even a slight expansion of bond lengths was observed. Up to two photons per molecule were absorbed at the higher nozzle pressures. At such pressures the maximum response was red shifted from that of the 300 K optical absorption band. Electron diffraction patterns taken a microsecond after excitation showed virtually complete V–V relaxation. Because little V–T relaxation took place in the jet expansion, the translational temperature downstream fell to 20 K while vibrational temperatures remained hot, at perhaps 500 K. The correspondence between the pumping of supersonic jets and the irradiation of static systems is briefly discussed.
Electron impact ionization cross section of metastable N2(A Σ+u)
Authors: Armentrout P. B. , Tarr Susan M. , Dori Ariel , Freund Robert S.
Published: February 2003

The nondissociative electron impact ionization cross section of the metastable N2(A 3Σ+u) state is measured from threshold to 240 eV. Rising from an appearance potential of 10.1±0.6 eV, the cross section peaks at about 40 eV with a value of (1.14±0.36)×10−16 cm2. These values are extracted from the apparent ionization cross section of an N2 beam composed of ∼50% N2(A 3Σ+u) and ∼50% N2(X 1Σ+g). This mixed state beam is formed by charge transfer neutralization of a 1 keV N+2 beam with NO. The N2(A 3Σ+u) cross section is normalized by measuring it relative to the ionization of a ground state N2 beam formed by charge transfer neutralization of N+2 with N2.
A classical trajectory study of the F+C2H4→C2H4F→H+C2H3F reaction dynamics
Authors: Hase William L. , Bhalla Kailash C.
Published: February 2003

The Monte Carlo classical trajectory method was used to study the dynamics of F+C2H4 recombination and the ensuing C2H4F decomposition. The trajectories were initiated at a relative translational energy of 20.0 kcal/mole with ethylene vibrating with its zero-point energy. Product energy distributions as well as velocity and angular momentum scattering angle distributions were calculated. The H+C2H3F relative translational energy distribution is statistical at the exit-channel saddle point. The nonstatistical relative translational energy distribution in the products arises from the centrifugal potential at the exit-channel saddle point and the potential energy release in the exit channel, of which approximately 80% goes to relative translation. Correlation coefficients were computed between various dynamic variables and many important correlations are found, primarily between the various angular momenta and the C2H3F rotational energy. A particularly significant correlation is the one between H+C2H3F orbital angular momentum at the exit-channel saddle point and in the products. The trajectory scattering angles and the energy distributions are compared with experimental studies of the reaction dynamics. It is pointed out that the statistical H+C2H3F relative translational energy distribution observed at the exit-channel saddle point does not necessarily imply a statistical unimolecular lifetime distribution for the excited C2H4F radicals.
Theoretical dipole derivatives for HCN and DCN
Authors: Lie G. C. , Peyerimhoff Sigrid D. , Buenker Robert J.
Published: February 2003

Hartree–Fock–Roothaan self-consistent-field (SCF) and multireference double-excitation configuration interaction (MRD–CI) methods have been used to compute the potential and dipole moment surfaces for the HCN molecule, from which a variety of molecular properties, such as equilibrium bond distances, force constants, equilibrium dipole moment and derivatives with respect to the normal coordinates, and integrated intensities for HCN and DCN, have been derived and compared with available experimental data. Satisfactory agreement is generally found between the MRD–CI and the experimental results, e.g., the calculated dipole derivatives with respect to the stretching normal coordinates are, with experimental values given in parentheses, −8.6 (±4.5) and −88.9 (±88) esu for HCN and −22.6 (±20) and −61.1 (±66) esu for DCN. Nevertheless, the calculated dipole derivatives with respect to the bending normal coordinate (80.1 and 46.4 esu, respectively, for HCN and DCN) are found to be much larger than the corresponding experimental values of 61 and 32 esu, discrepancies which would appear to be far too large to be attributed entirely to deficiencies in the present theoretical treatment.
Dynamics of hydroxyl radical desorption from a polycrystalline platinum surface
Authors: Talley L. D. , Sanders F W. A. , Bogan D. J. , Lin M. C.
Published: February 2003

Laser-induced fluorescence was used to determine the internal energy distribution of OH radicals desorbing from a polycrystalline Pt surface at T = 1130 K. The measurements were performed in a low-pressure flow system under conditions which were shown to be nearly collisionless by determining the energy distribution as a function of pressure. A Cu surface surrounding the reaction zone removed OH radicals efficiently and prevented scattering back into the laser beam. Both the rotational and vibrational temperatures were found to be equal to that of the Pt catalyst, suggesting that the product OH reaches thermal equilibrium with the surface at a rate which is greater than the rate of desorption. For the systems investigated (H2+O2, H2+NO2, H2O), the energy distributions were independent of the source of OH radicals.
Shear rigidity of spread stearic acid monolayers on water
Authors: Abraham B. M. , Ketterson J. B. , Miyano K. , Kueny A.
Published: February 2003

The effect of Al3+, Fe3+, Ca2+, and Mg2+ ions and of pH on the two-dimensional shear modulus of stearic acid spread on a water substrate was determined. A large shear modulus was displayed by the films when the subphase contained Al3+ and Fe3+ ions at the self-buffered pH. With Fe2+ dissolved in the subphase, the film displayed a viscous relaxation when strained but no residual stress was observed. No effect was observed with the Ca2+ or Mg2+. Reducing the pH value in the subphase with the trivalent ions caused the shear modulus to disappear. The observations are interpreted in terms of hydrogen bonding.
Two-photon spectroscopy of ultracold large molecules in planar supersonic expansions
Authors: Amirav A. , Even U. , Jortner Joshua
Published: February 2003

The vibronic spectrum of ultracold fluorene is reported. (AIP)
Influence of collisions on coherent IR multiphoton absorption in thiophosgene
Authors: Brenner D. M. , Spencer M. , Steinfeld J. I.
Published: February 2003

Absolute changes due to IR pumping in the intergrated rotational population of the vibrationless level (000000) of thiophosgene have been measured under beam conditions and bulb conditions (1–1000 mTorr). Under collisionless conditions, large decreases are observed which reflect depopulation of all rotational states at a single CO2 laser frequency. At higher thiophosgene pressure, less depopulation occurs; zero depopulation of the vibrationless level is observed at pressure ? 300 mTorr within experimental uncertainty (? 3%). The latter agrees with measurements of the average number of photons absorbed from photoacoustic data (0.013±0.001) obtained at a pressure of 500 mTorr. The results support a mechanism of coherent pumping in the low density of states regime and the existence of a long range, collision-induced dephasing interaction which has a cross section ≳≳ gas kinetic.
Radiative corrections for the hydrogen molecular ion HD+
Authors: Bishop David M. , Cheung Lap M.
Published: February 2003

Corrections to the vibrational energy levels of HD+ due to radiative effects are reported. (AIP)
Rate constants for the reaction of ground state atomic oxygen with methanol
Authors: Keil David G. , Tanzawa Tsuneo , Skolni Edward G. , Klemm R. Bruce , Michael Joe V.
Published: February 2003

The reaction of O(3P) with methanol has been studied using the complementary discharge flow and flash photolysis techniques. In both cases, resonance fluorescence detection of atomic oxygen was employed. The discharge flow (DF) apparatus was used in a temperature range of 298–998 K while the flash photolysis (FP) apparatus was used in the overlapping range of 329–527 K. The apparent bimolecular rate constants for the O-atom/methanol reaction obtained from DF experiments at low temperatures (T?450 K) were independent of both the initial O-atom concentration and the mode of O-atom production. In addition, large excesses of O2 were added to the flow to intercept the primary reaction product (CH2OH), but had no apparent effect on the measured rate constant. Results from the two methods were in good agreement within this limited temperature range (∼300–500 K). At temperatures above ∼450 K, the apparent rate constants obtained from DF experiments were increasingly sensitive to the O2 concentration, with the rate constants being smaller when determined in the presence of large [O2]. Since the initial O-atom concentrations were on the order of 1011 or less, a simple stoichiometry effect can be ruled out. However, the results of the present kinetic experiments indicated that heterogeneous pyrolysis of CH3OH may have occurred in the flow system. This observation is consistent with studies of the adsorption of methanol on silica surfaces. This problem was apparently overcome by adding small amounts of O2 and the rate constants obtained in this way were seen to agree well with values extrapolated from the lower temperature DF and FP experiments. The rate data from DF and FP experiments were thus combined to obtain the following Arrhenius expression (298–998 K): k1 (T) = (2.70±0.50)×10−11 exp(−5030±160/RT cm3 molecule−1 s−1. This result is compared with those of previous studies, and kinetic complications (stoichiometry) and heterogeneous effects are further discussed.
Theory of electrical conduction in organic molecular crystals. III. Temperature-independent mobilities in naphthalene
Authors: Sumi H.
Published: February 2003

Temperature-independent electron mobilities (TIEM) observed in two crystal axes (b and c′) in naphthalene are explained by an extension of a model which was proposed previously [H. Sumi, J. Chem. Phys. 70, 3775 (1979); 71, 3403 (1979)] to explain TIEM observed in anthracene only in a single crystal axis (c′). The electron mobility in the a direction, which decreases with increasing temperature, is postulated to arise from electron motion in a one-dimensional Bloch band along the a axis. TIEM in the b and c′ directions arises because electrons hop from one a-axis Bloch band to another because of a transfer integral induced by thermal rotational vibrations of molecules. An important feature in the model is that sharp peaks in the density-of-state function of the one-dimensional band are rounded by the broadening due to phonon scattering.
Tunneling states in methane at high pressures
Authors: Eckert J. , Fincher C. R. , Goldstone J. A. , Press W.
Published: February 2003

Rotational tunneling states in phases II and III of solid CH4 were studied by inelastic neutron scattering techniques at 8 K and pressures up to 850 bar. The tunnel energies were found to depend strongly on pressure, while the rotational peak of the disordered molecules shifts little with pressure up to the II–III phase transition. In phase III, additional intensity was found at about 0.18 meV, which we interpret as tunneling states for those molecules that are disordered in phase II.
Tests of approximation schemes for vibrational energy levels and partition functions for triatomics: H2O and SO2
Authors: Isaacson Alan D. , Truhlar Donald G. , Scanlon Kerin , Overend John
Published: February 2003

Various approximate schemes are used to obtain vibrational energy levels and partition functions for H2O and SO2. These results are then compared with accurate quantum mechanical values computed for the same original quartic force fields. The neglect of interaction force constants in internal coordinates and the use of a Morse model to describe stretching anharmonicity are both shown to provide reasonably accurate perturbation theory energy levels and partition functions, while the neglect of interaction force constants in normal coordinates is found to yield much less accurate results. In addition, the method of Pitzer and Gwinn to calculate partition functions without first calculating energy levels is shown to provide a good approximation to the accurate partition functions.
A molecular dynamics study of water microclusters surrounding a phosphate ion
Authors: Lee W. K. , Prohofsky E. W.
Published: February 2003

Molecular dynamics calculations similar to those developed for pure water by Rahman and Stillinger have been carried out for clusters of PO43−(H2O)n, where n = 6, 12, and 18. It was found that the water molecules are distributed in one, two, and three hydration shells in the n = 6, n = 12, and n = 18 clusters, respectively. There is exchange of water molecules between the hydration shells. The density profile and the velocity autocorrelation functions of the hydrogen and oxygen atoms of the water molecules are reported. For the n = 6 cluster and the first hydration shell of the n = 12 cluster the velocities of the hydrogen and oxygen atoms of the water molecules are resolved into three components in accordance with the symmetry of the phosphate ion. The autocorrelation functions of these velocity components exhibit simple time dependences.
Thermodynamic properties of water under pressure up to 5 kbar and between 28 and 120 °C. Estimations in the supercooled region down to −40 °C
Authors: Ter Minassian Leon , Pruzan Philippe , Soulard Alain
Published: February 2003

The heat liberated by isothermal compression permits the determination of the thermodynamic properties of liquid water−heat capacity, compressibility, and expansivity. The results, as a function of pressure and temperature, have been extrapolated as far down as −40 °C. They confirm the existing data in the region of the supercooled liquid and also the existence of a divergence of the measured properties. This could be explained as a lambda transition occuring at −45 °C on isobars p = 0. The abnormal heat capacity which characterizes this transition is well described as a function of the temperature by a formula with critical coefficients as already suggested by others.
Energy levels of Nd3+ in LiYF4
Authors: da Gama A. A. S. , de Sá Gilberto F. , Porcher P. , Caro P.
Published: February 2003

High-resolution absorption spectra of Nd3+ in LiYF4 were recorded between 3900 and 40 200 cm−1 at temperatures from 10 to 300 K. The levels were obtained by diagonalizing a Hamiltonian that describes the free ion parameters, including two and three-body configuration interactions, as well as the crystal field operator. Calculations were performed using the complete basis of 364 ‖αSLJMj〉 kets of the 4f3 configuration of Nd3+. A set of free ion and crystal field parameters were calculated which fitted energy levels with an rms deviation of 22 cm−1 with respect to 134 experimentally determined levels.
Calculations of zero-field splittings in pyridine derivatives
Authors: Motten Ann G. , Davidson Ernest R. , Kwiram Alvin L.
Published: February 2003

Zero-field splittings were calculated for benzene, pyridine, and a number of simple derivatives. The experimental decrease of the zfs parameter D upon addition of substituents on the benzene and pyridine rings and upon protonation of pyridine was reproduced theoretically without invoking either aplanarity or nπ* interaction. For a lowest ππ* triplet state of pyridine, D = 0.165 cm−1 and E = −0.020 cm−1 are predicted. Zfs integrals were calculated from a wave function formed from CNDO/2 orbitals with two-configuration CI, using a five-term Gaussian expansion with the best Slater exponents for atoms in molecules.
A general theory for collision-induced absorption in molecules
Authors: Moon Molly , Oxtoby David W.
Published: February 2003

We present a general theory for the dipole moment induced electrostatically in a pair of colliding molecules. Each molecule is placed in a weak, uniform external field and its charge distribution expanded in that field. The Coulombic interaction between these molecules is then expressed as an expansion in the external field; the coefficient of the linear term gives the induced pair dipole. The contributions from field gradients arise naturally in our approach. The spectral integrals γ and α have been calculated; our general expression can be used for overlapping as well as separated molecules. The asymptotic limit is evaluated explicitly for molecules of D∞h and Td symmetry. Our results show the role played by field gradients and raise serious doubts about the validity of previous determinations of higher-order multipole moments from collision-induced absorption spectra.
The rotational spectrum and molecular geometry of the cyclopropane–HF dimer
Authors: Buxton L. W. , Aldrich P. D. , Shea J. A. , Legon A. C. , Flygare W. H.
Published: February 2003

Four isotopic species of a hydrogen-bonded dimer formed between cyclopropane and HF have been observed through assignment of their rotational spectra using a pulsed, Fourier-transform microwave spectrometer in which a gas mixture is pulsed into an evacuated Fabry–Perot cavity. The geometry of the dimer has unambiguously been shown to have HF perpendicular to the cyclopropane edge and in the plane of the ring. HF, on average, lies on the C2 symmetry axis of the dimer which is additionally the a principal axis. Hyperfine structure due to the spin–spin interaction in HF and DF was resolved as well as the hyperfine structure due to the nuclear quadrupole moment of deuterium in the cyclopropane–DF species. The following spectroscopic constants have been obtained for the cyclopropane–HF species: The rotational constants are A = 19 948(60), B = 2753.706(2), and C = 2539.115(2) MHz, the HF spin–spin constant is 121(43) kHz, and the centrifugal distortion constants are DJ = 5.08(27) and DJK = 43.5(36) kHz.
Electron spin echo studies of Cu2+ on silica surfaces: Interaction with water and ammonia adsorbates
Authors: Ichikawa Tsuneki , Yoshida Hiroshi , Kevan Larry
Published: February 2003

An electron spin echo modulation study of cupric ion exchanged into silica gel by an ammonia complex shows that Cu2+ is coordinated to only two NH3 molecules. This coordination is reversible by thermal activation. Adsorption of H2O instead of NH3 also shows coordination to only two H2O molecules which is thermally reversible. From these electron spin echo results and electron spin resonance spectra, it is postulated that in the presence of adsorbate the cupric ion has a distorted octahedral environment involving coordination to two adsorbate molecules and four lattice oxygens.
Radiation damage of CrO42− doped KH2PO4 single crystals
Authors: Chowdari B. V. R. , Sekhar Y. Ravi
Published: February 2003

Radiation damage studies of CrO42− ions doped in KH2PO4 crystals are presented. The optical absorption spectra of these crystals before irradiation show characteristic bands around 3600 and 2700 Å. The optical spectra after irradiation show new absorption bands in the region 5000–7000 Å. EPR spectra of the irradiated crystals consist of a single line at RT which shows splitting at low temperatures. By a systematic correlation of the optical absorption and EPR results at different stages of irradiation, the radiation damage product of these crystals is identified as CrO43−. The analysis of EPR spectra shows axial symmetry for CrO43− in the paraelectric phase with g∥ = 1.955 and g⊥ = 1.972 and orthorhombic symmetry in the ferroelectric phase with gx = 1.983, gy = 1.976, and gz = 1.945.
Zeeman study of a boron trichloride single crystal by pulsed FT NQR spectroscopy
Authors: Litzistorf Gilbert , Sengupta Sankar , Giezendanner Daniel , Lucken E. A. C.
Published: February 2003

A 35Cl Zeeman NQR study of a single crystal of boron trichloride yields the value of the field-gradient asymmetry parameter of 0.557±0.011, in agreement with previous values of 0.54 and 0.50 obtained from studies of polycrystalline samples. Apart from the well known doublet due to an isotope effect, further fine structure whose details depend on the orientation of the Zeeman field is observed. It is shown that this fine structure arises from 11B–35Cl dipole–dipole interaction.
The generalized resonating valence bond method: Barrier heights in the HF + D and HCl + D exchange reactions
Authors: Voter Arthur F. , Goddard William A.
Published: February 2003

A method of self-consistent optimization of a resonating wave fuction is developed and applied to the reaction HF+D?H+FD. (AIP)
Outer-shell photoionization of the beryllium isoelectronic sequence
Authors: Ganas P. S.
Published: February 2003

The results of calculations for the photoionization cross sections for the isoelectronic sequence BeI, BII, CIII, NIV and OV are presented. (AIP)
The inversion barriers of PH3, PH2F, PHF2, and PF3
Authors: Boggs James E. , Seida David
Published: February 2003

The inversion barriers of PH3, PH2F, PHF2, and PF3 were calculated using the SP bais set of Ref. 1. The calculations were made using program moleculem and results are given in table 1. (AIP)
Comment on the ‘‘Energy level analysis of Np3+:LaCl3 and Np3+:LaBr3’’
Authors: Poon Y. M. , Newman D. J.
Published: February 2003

The scaling of the crystal field parameter in the energy level analysis of Carnall et al. for Np3+:LaCl3 and Np3+:LaBr3 is questioned.(AIP)