bluuebunny/crossref_metadata_2025 huggingface dataset:
Low field anisotropic magnetostriction of single domain exchange-coupled (TbFe/Fe) multilayers
Authors: Le Gall H. , Youssef J. Ben , Socha F. , Tiercelin N. , Preobrazhensky V. , Pernod P.
Published: July 2002

Giant magnetostriction (GMS) reported until now in exchange-coupled multilayers (ECML) present quasi-isotropic magnetostrictive behavior. In the present work it is shown the possibility to induce highly anisotropic GMS at low field with the single domain state in (TbFe/Fe)n multilayers when deposited by ion sputtering under a magnetic polarization field Hd. ECML grown under bias field Hd, applied along the large size of rectangular glass substrates present original magnetic and magnetoelastic (ME) properties associated with strong uniaxial behavior. After saturation by an external field H∥ applied parallel to the easy axis induced by Hd, a single domain state is kept by decreasing H∥ down to zero (Mr/Ms=1) which explains why there is no change of the magnetoelastic coefficient bγ,2 by increasing or decreasing H∥. A different behavior arises along the hard magnetization axis with a strong change of bγ,2 by increasing H∥ up to the saturation. ME anisotropy is the origin of high amplitude flexural and torsional oscillation modes as observed in our ECML.
The temperature, concentration phase diagram for Tb1−xDyxZn: Failure of crystal field theory
Authors: Cullen J. , Wang K. , Segnan R.
Published: July 2002

We have calculated the free energy of a crystal field model designed to reproduce the magnetic temperature, composition phase diagram for Tb1−xDyxZn alloys. Using fourth- and sixth-order coefficients consistent with single-ion theory, it was found to be impossible to reproduce the experimental phase boundaries. A reasonable fit to the entire diagram was obtained when the coefficients were chosen to be of the same sign for Dy and Tb, rather than of opposite sign, as required by single-ion theory. To explain this discrepancy, a model is introduced which includes a contribution to the crystal field coming from quadrupole–quadrupole interactions. It is argued that the reason for the success of the calculation using coefficients of the same sign is directly related to the dependence of the strength of the quadrupole coupling on the square of the second-order Stevens factor.
Kinetics of porous silicon growth studied using flicker-noise spectroscopy
Authors: Parkhutik V. , Timashev S.
Published: July 2002

The mechanism of the formation of porous silicon (PS) is studied using flicker noise spectroscopy (FNS), a new phenomenological method that allows us to analyze the evolution of nonlinear dissipative systems in time, space and energy. FNS is based on the ideas of deterministic chaos in complex macro- and microsystems. It allows us to obtain a set of empiric parameters (“passport data”) which characterize the state of the system and change of its properties due to the evolution in time, energy, and space. The FNS method permits us to get new information about the kinetics of growth of PS and its properties. Thus, the PS formation mechanisms at n-Si and p-Si, as revealed using the FNS, seem to be essentially different. p-Si shows larger “memory” in the sequence of individual events involved in PS growth than n-Si (if anodized without light illumination). The influence of the anodization variables (such as current density, HF concentration, duration of the process, light illumination) onto the “passport data” of PS is envisaged. The increase of the current density increases memory of the PS formation process, when each forthcoming individual event is more correlated with the preceding one. Increasing current density triggers electrochemical reactions that are negligible at lower currents. Light illumination also produces a positive effect onto the “memory” of the system. The FNS makes it possible to distinguish different stages of the continuous anodization process which are apparently associated with increasing pore length. Thus, FNS is a very sensitive tool in analysis of the PS formation and other complex electrochemical systems as well.
Behavior and effects of fluorine in annealed n+ polycrystalline silicon layers on silicon wafers
Authors: Marsh C. D. , Moiseiwitsch N. E. , Booker G. R. , Ashburn P.
Published: July 2002

A comprehensive study is made of the behavior and effects of fluorine in n+-polysilicon layers. The polysilicon is deposited in a conventional low pressure chemical vapor deposition furnace on (100) silicon wafers, implanted with 1×1016 cm−2 F+ and 1×1016 cm−2 As+ and annealed at 850, 950, 1015, and 1065 °C. Sheet resistance, transmission electron microscopy (TEM), and secondary ion mass spectroscopy are used to obtain quantitative data for the breakup of the interfacial oxide, the epitaxial regrowth of the polysilicon layer, and the fluorine and arsenic distributions. The fluorine significantly increases both the initial oxide breakup (∼8×) and the initial polysilicon regrowth. It also produces inclusions in the layer which can affect the subsequent polysilicon regrowth and the arsenic distributions. Three regrowth stages and two regrowth mechanisms are distinguished and interpreted, and a value of ∼6×10−11 cm2 s−1 is deduced for the effective diffusivity of fluorine in polysilicon at 950 °C. The amounts of regrowth determined by TEM are compared with the corresponding changes in sheet resistance. The thermal budgets required to produce polysilicon layer regrowths of 1% and 50%, important for the performance of polysilicon emitter bipolar transistors, are given. All the thermal budgets are lower when fluorine is present.
Approximating the magnetic recording step response using a Voigt function
Authors: Stupp Steven E.
Published: July 2002

A simple, closed-form expression for the step response or pulse shape of a magnetic recording channel is described. The step responses of inductive and magnetoresistive heads with thin-film media are shown to be well approximated by a Voigt function (the convolution of a Lorentzian and a Gaussian function). For convenience, an accurate approximation to the Voigt function (the linear superposition of a Lorentzian and a Gaussian function with appropriate weighting) was fit to the step responses using one adjustable parameter. The improved accuracy of this approximation to the step response has a strong impact on channel performance analysis and modeling.
Electrical noise from phase separation in Pr2/3Ca1/3MnO3 single crystal
Authors: Anane A. , Raquet B. , von Molnár S. , Pinsard-Godart L. , Revcolevschi A.
Published: July 2002

Low frequency electrical noise measurements have been used to probe the electronic state of the perovskite-type manganese oxide Pr2/3Ca1/3MnO3 versus temperature and in the vicinity of the field-induced transition from the insulating, charge-ordered (I-CO) state to the metallic, ferromagnetic state (M-F). At high temperature we have observed a high level of the excess noise with mainly a Gaussian distribution of the resistance fluctuations, and the associated power spectral density has a standard 1/f dependence. However, in the hysteretic region, where the electrical resistance depends dramatically on the sample history, we have observed a huge non-Gaussian noise characterized by two level fluctuator-like switching in the time domain. We discuss the origin of the noise in terms of percolative behavior of the conductivity. We speculate that the dominant fluctuators are manganese clusters switching between the M-F and the I-CO phases.
Magnetism and heavy fermions in YbRhSn and YbPtSn
Authors: Andraka Bohdan , Pietri Richard , Kaczorowski Dariusz , Leithe-Jasper A. , Rogl P.
Published: July 2002

Isostructural YbRhSn and YbPtSn were studied by specific heat, electrical resistivity, and magnetoresistance. Both compounds order antiferromagnetically below 2 and 3.5 K, respectively. Above 4 K, they display a number of remarkable similarities including Kondo-like resistivity and large negative magnetoresistance. Scaling analysis of this magnetoresistance shows that it is due to the suppression of Kondo scattering in YbRhSn but has a ferromagnetic spin fluctuation character in YbPtSn. The heavy fermion state was confirmed in YbRhSn by low temperature specific heat measurements yielding γ of about 1200 mJ/K2 mol. γ for YbPtSn is of order 100 mJ/K2 mol only.
Effect of silicon crystal structure on spin transmission through spin electronic devices
Authors: Loraine Duncan R. , Pugh David I. , Jenniches Hartmut , Kirschman Randall , Thompson Sarah M. , Allen Will , Sirisathikul Chitnarong , Gregg John F.
Published: July 2002

Spin injection into and spin transport through silicon spacer layers in iron/silicon/cobalt structures has been investigated. Ultrahigh vacuum evaporated silicon spacers of varying crystal quality from amorphous to epitaxial of thicknesses from 10 to 200 Å were shown to improve their electrical conduction with increasing crystallinity, but no spin dependent transport was observed through the structure. Silicon and iron interdiffusion was also observed at the interfacial region. Device quality silicon was studied using 460 and 540 μm doped silicon wafers of resistivity 0.1 and 1 Ω cm, respectively, polished on both sides, onto which were deposited iron and cobalt layers. Sharp metal-semiconductor interfaces were achieved in this way, but no spin dependent transport, putting an upper limit on the spin diffusion length in device quality silicon wafers.
Ferromagnetic resonance of amorphous Fe–Hf thin films
Authors: Baek Jong-Sung , Kim Yark-Yeon , Lim Woo-Young , Bong Chung-Jong , Lee Soo-Hyung
Published: July 2002

In order to examine the dependence of magnetic properties of amorphous Fe100−xHfx (x=20, 25, and 30 at. %) thin films on the Hf content and the film thickness, we investigate the ferromagnetic resonance (FMR) spectra. The samples were deposited on silicon substrate by dc magnetron sputtering method. The thicknesses of the films were 100, 200, and 300 nm. To obtain values, such as effective magnetization Meff, spectroscopic splitting factor g, exchange stiffness constant A, and surface magnetic property, FMR measurements were carried out with the static magnetic field perpendicular and parallel to the film plane at room temperature. The g values are about 2.10 for almost all samples. In 300 nm thick samples the A decreases rapidly from 1.47×10−6 to 0.70×10−6 erg/cm as the Hf content increases up to 30 at. %. In 100 and 200 nm thick samples the A decreases a little with increasing Hf content. When the Hf content is increased up to 30 at. % the surface magnetic anisotropy constant Ks2 of the film–substrate interface increases slightly from −0.22 to 0.02 erg/cm2 but the surface magnetic anisotropy constant Ks1 of the film–air interface increases rapidly from −0.61 to −0.22 erg/cm2 for 300 nm thick samples.
Phase formation and magnetic properties of Nd3(Fe,Co,Ti)29 compounds
Authors: Tang N. , Yin X. Y. , Yang D. , Wang J. L. , Wu G. H. , Yang Fuming , Shen Y. P. , Zhong X. P.
Published: July 2002

Nd 3 (Fe,Ti ) 29−x Co x compounds with Nd3(Fe,Ti)29-type structure have been synthesized with x=0, 1.61, 3.22, 4.83, and 6.44. The easy magnetization directions of all these compounds are found to be in the basal plane. The Curie temperature increases strongly with increasing Co content. Substitution of Co for Fe leads to a monotonic increase of the saturation magnetization. The spin reorientation transitions are found for all of these compounds, and the spin-reorientation temperature decreases with increasing Co content.
Theoretical studies of the reactions of HCN with atomic hydrogen
Authors: Bair Raymond A. , Dunning Thom. H.
Published: July 2002

A comprehensive theoretical study has been made of the energetics of the important pathways involved in the reaction of hydrogen atoms with hydrogen cyanide. For each reaction ab initio GVB-CI calculations were carried out to determine the structures and vibrational frequencies of the reactants, transition states, and products; then POL-CI calculations were carried out to more accurately estimate the electronic contribution to the energetics of the reactions. The hydrogen abstraction reaction is calculated to be endoergic by 24 kcal/mol [expt. ΔH (0 K)=16–19 kcal/mol] with a barrier of 31 kcal/mol in the forward direction and 6 kcal/mol in the reverse direction. For the hydrogen addition reactions, addition to the carbon atom is calculated to be exoergic by 19 kcal/mol with a barrier of 11 kcal/mol, while addition to the nitrogen center is essentially thermoneutral with a barrier of 17 kcal/mol. Calculations were also carried out on the isomerization reactions of the addition products. The cis→trans isomerization of HCNH has a barrier of only 10 kcal/mol with the trans isomer being more stable by 5 kcal/mol. The (1,2)-hydrogen migration reaction, converting H2CN to trans-HCNH, is endoergic by only 14 kcal/mol, but the calculated barrier for the transfer is 52 kcal/mol. The energy of the migration pathway thus lies above that of the dissociation–recombination pathway.
Total electron yield measurements of extended x-ray absorption fine structures (EXAFS) of Ni and Fe thin foils, and adsorption of Ni on polycrystalline Fe substrates
Authors: Sham T. K. , Carr R. G.
Published: July 2002

X-ray absorption spectra of Fe and Ni K edges have been obtained at room temperature by means of a total electron yield technique for a clean Fe foil on which Ni was subsequently deposited, and a Ni foil. This technique involves the measurement of the specimen current. The total yield is found to be ∼1×10−2 electron per photon absorbed at the Fe K edge for a 1/4 mil foil. Dramatic increase in surface sensitivity is gained over transmission EXAFS by using this technique to study Ni overlayers on Fe surface. The EXAFS of the deposited Ni overlayers (several monolayer coverage) are compared with those of the pure elements and of Ni/Fe alloys in the α(bcc) and γ(fcc) phases. The results indicate that the average Ni–Ni bond in the deposited Ni overlayers does not contract relative to that in the bulk in contrast to previously observed contraction of Ni deposition on carbon substrates. The feasibility of this technique and its application are discussed.
Kinetic studies of the reaction of the SO radical with NO2 and ClO from 210 to 363 K
Authors: Brunning J. , Stief L. J.
Published: July 2002

The rates of the reactions of the SO radical with NO2 and ClO have been determined in a discharge flow system near 1 Torr pressure with detection of radical and molecular species using collision-free sampling mass spectrometry. The rate constants were determined from the decay of SO radicals in the presence of an excess of NO2 and ClO. The NO2 reaction was studied between 210 and 363 K and found to be temperature invariant: SO+NO2→SO2+NO; k1=(1.37±0.10)×10−11 cm3 s−1. Similarly, the ClO reaction was observed to be independent of temperature in the interval from 248 to 363 K: SO+ClO→SO2+Cl; k2=(3.22±0.48)×10−11 cm3 s−1. Comparison is made with previous studies of these reactions at room temperature and with other radical–radical reactions involving SO or ClO.
Gerade electronic states of Xe2 observed using resonantly enhanced multiphoton ionization
Authors: Dehmer P. M. , Pratt S. T. , Dehmer J. L.
Published: July 2002

The two photon resonant, three photon ionization spectrum of the rare gas dimer Xe2 was determined in the energy region of the Xe* 5d and 6p states. A number of new band systems were observed that arise from two photon transitions from the ground state to bound vibrational levels of excited states of gerade symmetry. The analysis of the observed vibronic structure of these band systems provides new information on the dissociation energies and the potential energy curves of the low-lying dipole forbidden excited states of Xe2.
The microwave spectrum of the PF2 radical in the X̃ 2B1 ground vibronic state
Authors: Saito Shuji , Endo Yasuki , Hirota Eizi
Published: July 2002

The microwave spectrum of the PF2 radical in the X̃ 2B1 ground vibronic state was observed by using a source modulation spectrometer. The radical was produced in a free-space absorption cell by a dc glow discharge in a mixture of PH3 and CF4, and 260 spectral lines were observed in the frequency region of 63–181 GHz and were assigned to 37 rotational transitions. The observed lines were least-squares analyzed to determine the rotational constants, centrifugal distortion constants, spin-rotation coupling constants with centrifugal distortion correction terms, and magnetic hyperfine coupling constants for both the phosphorus and fluorine nuclei. The εaa spin-rotation coupling constant was found to be very small: −30.041 MHz, suggesting that excited electronic states contributing to εaa are all high lying or their contributions have canceled each other. The r0 structure of PF2 was calculated from the observed rotational constants: r0(P–F)=1.5792(18) Å and θ0(FPF)=98.48 (21)° with uncertainties in parentheses. The vibrational frequencies were estimated from the observed centrifugal distortion constants to be ω1=864(14), ω2=365.3(11), and ω3=848(24) in cm−1. The Tcc dipolar hyperfine coupling constants give the spin density of the unpaired electron orbital to be 92.1% and 8.1% at P and each of F, respectively, whereas the aF Fermi coupling constants lead to the s characters of 1.64% and 0.18% at the two atoms.
The submillimeter-wave spectrum of the HCCO radical
Authors: Endo Yasuki , Hirota Eizi
Published: July 2002

The pure rotational spectra of the HCCO and DCCO radicals were observed for the first time in the submillimeter-wave region. The HCCO radical was generated by either the C2H2+O reaction or the H2CCO+F reaction. The former was found to be about twice as efficient as the latter, and was employed for obtaining DCCO using C2D2 as a precursor. The observed spectra were fitted to the pattern of a near prolate symmetric top with a large A rotational constant. The observed spin-rotation splittings result in an extremely large εaa constant and exhibit an anomalous K dependence, indicating that there is a low-lying excited electronic state which interacts with the ground state.
Simple model for liquid water
Authors: Sánchez Gabriel , Costas María Eugenia , Varea Carmen
Published: July 2002

We present a simple model for the thermodynamic behavior of liquid water. The enhanced interactions and open structure of the hydrogen bond are modeled on the average by a simple van der Waals mixture of two interchangeable components. All the anomalous thermodynamic behavior of liquid water is predicted by the model.
Molecular dynamics study of a dipolar fluid between charged plates. II
Authors: Lee Song Hi , Rasaiah Jayendran C. , Hubbard J. B.
Published: July 2002

Further molecular dynamics simulations of thin films of Stockmayer molecules between Lennard-Jones plates are discussed when the distance h between the plates ranges from 2.25 σ to 9.5 σ, where σ is the molecular diameter, and the electric field E ranges between 0 and 1010 V/m. The solvation force is calculated as a function of the plate separation h when E=0 and E=109 V/m and as a function of the field E when h=4.0 σ and 7.5 σ. We also study the system when h=2.25 σ and 4.0 σ with the field E ranging from 0 to 1010 V/m and find that the monolayer system (h=2.25 σ) seems to undergo changes of state as the temperature is lowered at zero field or if the field is changed at low temperature. While, in the absence of a field, the molecules tend to form loops and chain-like structures with the dipoles parallel to the wall, a strong external field orients the dipoles along the field so that the long-range repulsive interaction appears to induce a transition to an imperfect (two-dimensional) triangular lattice at low temperature. In between these states, at low temperatures and high fields, the molecules are packed in parallel chains with their moments perpendicular to the field and in ‘‘ferroelectric domains’’ of opposite polarization.
Microwave spectra and structure of HI–HF complexes
Authors: Bumgarner R. E. , Kukolich S. G.
Published: July 2002

Microwave spectra for the HI–HF, HI–DF, DI–HF, and DI–DF complexes were measured using a pulsed-beam, Fourier-transform microwave spectrometer. Rotational transitional transitions were measured over the 4–18 GHz range to an accuracy of 5 kHz. The spectroscopic constants obtained by fitting the observed transitions for the series HI–HF, HI–DF, DI–HF, and DI–DF are, respectively: (B+C)/2=2220.7482(8), 2173.236(2), 2209.623(4), and 2162.884(6) MHz; eQq(I)=687.01(2), 693.63(5), 725.96(4), and 727.8(1) MHz; ΔeQq(I)=−42(2), −50(6), −210(14), and −141(25) kHz; DJ =8.86(3), 8.25(6), 8.1(6), and 8.6(5) kHz. This complex has an interesting triangular structure with the H–I and H–F bonds making an acute angle of 70.1 (2.8)°. The iodine atom is coaxial with HF with a heavy atom separation R0(I–F)=3.660(8) Å. Hyperfine structure due to deuterium quadrupole coupling and H–F spin–spin interactions was resolved and measured.
Triplet states of CO trapped in rare gas crystals
Authors: Bahrdt J. , Gürtler P. , Schwentner N.
Published: July 2002

Vibrational progressions due to the a 3Π, a′ 3Σ+, d 3Δ, and e 3Σ− states of CO in Ar, Kr, and Xe crystals are observed in absorption. Two groups of phonon sidebands separated from the zero phonon lines by about 4 and 8 meV for the a′ 3Σ+ and d 3Δ states are attributed to librations and to localized phonons. The broad absorption bands, the even broader emission bands, and the large Stoke shift of the a 3Π transition are treated in terms of a configuration coordinate model by a momentum analysis. A quadratic coupling has to be invoked with relaxation energies in the excited states increasing from 14 meV for Ar to 95 meV for Xe and with relaxation energies in the ground state increasing from 29 meV for Ar up to 1278 meV for Xe. The changes of the configuration coordinate of 0.2 to 1.5 Å are also discussed with the help of two pair potential models.
Transient effects in monomer–excimer kinetics
Authors: Sienicki K. , Winnik M. A.
Published: July 2002

A theoretical model for diffusion-controlled excimer formation in the presence of excimer dissociation is presented. We assume that the rate coefficient for excimer formation k1(t) has the form k1(t)=a+bt−1/2. The equations obtained for monomer and excimer fluorescence decays are given in terms of Laplace transforms. Numerical analysis of monomer and excimer fluorescence decays are given in order to show the influence of dissociation, diffusion, and solution concentration on fluorescence decays. It has been shown that dissociation leads to exponentialization of decay curves. Two different methods of calculation quantum yields of monomer and excimer fluorescence are given in the case of time-dependent excimer formation and dissociation.
Laboratory measurement of the permanent electric dipole moment of gas-phase CuO in its X 2Π state
Authors: Steimle T. C. , Nachman D. F. , Fletcher D. A.
Published: July 2002

A sub-Doppler optical Stark measurement of the P1(1.5) branch feature of the A 2Σ−(v′=0)–X 2Π3/2(v″=0) subband system of gas phase copper monoxide, CuO, has been performed. The observed Stark shifts have been analyzed and a permanent electric dipole moment of 4.45±0.30 D (1σ error estimate) for the X 2Π3/2 state determined. The results are discussed in terms of the various bonding models proposed for CuO.
An extended study of the lowest Π bending vibration–rotation spectrum of Ar–HCl by intracavity far infrared laser/microwave double resonance spectroscopy
Authors: Robinson Ruth L. , Ray Douglas , Gwo Dz-Hung , Saykally Richard J.
Published: July 2002

The lowest Π bending state in Ar–HCl has been more completely characterized through the use of far infrared laser/microwave double resonance spectroscopy. This extended analysis includes a partial reassignment of the far infrared spectra of Ar–H35Cl previously reported by Ray et al. and by Marshall et al., as well as an analysis of the ArH37 Cl spectra. Improved molecular constants have been determined. The value of the rotational constant is now in good agreement with that calculated by Hutson from the M5 double minimum potential surface. Along with the recently reported spectrum of the Σ bending vibration, this extended analysis provides strong evidence for the existence of two minima character in the intermolecular potential surface of Ar–HCl.
The orientation of Langmuir–Blodgett monolayers using NEXAFS
Authors: Outka D. A. , Stöhr J. , Rabe J. P. , Swalen J. D.
Published: July 2002

Carbon K-shell NEXAFS (near edge x-ray absorption fine structure) spectra of oriented hydrocarbon chains in Langmuir–Blodgett (LB) monolayers were measured and used to study the orientation of these molecules. The LB monolayers were assembled from arachidic acid or cadmium or calcium arachidate on the oxidized Si(111) surface. The observed NEXAFS resonances are assigned to transitions to excited states which are localized on individual CH2 groups or C–C bonds. From a detailed analysis using curve-fitting techniques of the angular dependence of the various spectral peaks, the hydrocarbon chains of the cadmium arachidate monolayer is estimated to lie within 15° of the surface normal, the hydrocarbon chains of the calcium arachidate monolayer is estimated to be tilted by 33±5° from the surface normal, while the arachidic acid monolayer is not ordered at all. The determined chain orientations are discussed in terms of a microscopic model involving lateral interactions between the zig–zag hydrocarbon chains.
Rotational energy transfer in D2CO (v4=1): IR–UV double resonance studies of J-changing collisions
Authors: Bewick C. P. , Haub J. G. , Hynes R. G. , Martins J. F. , Orr B. J.
Published: July 2002

The technique of time-resolved infrared–ultraviolet double resonance (IRUVDR) spectroscopy is used to characterize the rate and mechanism of state-to-state rotational energy transfer (RET) in D2CO/D2CO collisions. The investigations employ CO2-laser irradiation to prepare a D2CO molecule in the v4=1, (J,Ka) =(18,11) rovibrational level of its X̃ 1A1 electronic ground state. Vapor-phase collisions with other D2CO (v=0) molecules then induce RET, with IRUVDR-monitored quantum-number changes ΔJ for the state-selected molecule ranging between +3 and −7. Kinetic modeling of the resulting experimental data shows that the inelastic cross sections for such J-changing rotational relaxation can be described adequately by simple scaling laws based on the rotational energy change ‖ΔE‖ for the state-selected molecule, with a power-gap fitting law proving marginally superior to an exponential-gap fitting law. The range of ‖ΔJ‖ monitored in these experiments is sufficiently extensive to discredit a simple propensity-rule fitting law, comprising consecutive collision-induced processes with individual changes ‖ΔJ‖ confined to values of 1 or 2. The microscopic rate constants derived reflect the dominance of ΔJ=±1 contributions for J-changing RET in D2CO/D2CO collisions, owing to long-range dipole/dipole interactions. These results elucidate RET in collisions between a pair of dipolar polyatomic (D2CO) molecules at a level of detail usually confined to studies of dipolar diatomic molecules, such as HF. Less detailed IRUVDR results, for RET in self-collisions of HDCO and for D2CO colliding with a variety of foreign-gas molecules, are also presented.
A classical path approach to reactive scattering. I. Use of hyperspherical coordinates
Authors: Muckerman J. T. , Gilbert R. D. , Billing G. D.
Published: July 2002

A classical path method is described for treating reactive collisions in three-body systems. The key feature of the method is the use of hyperspherical coordinates, which allow the definition of classical and quantum subsystems in such a way as to be independent of the arrangement of the particles. The ‘‘relative’’ motion and overall rotation are treated classically, while the ‘‘arrangement’’ and internal motion are treated quantum mechanically. The method is applied to the collinear D+HH system on the PK2 potential energy surface. These calculations show a great improvement over quasiclassical trajectory results in the vicinity of the apparent threshold of the reaction.
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o calculation and anharmonic force field of hypochlorous acid, HOCl
Authors: Halonen L. , Ha T.-K.
Published: July 2002

A b initio calculations on HOCl have been performed at the third-order Mo/ller–Plesset perturbation theory level to determine the equilibrium structure and the anharmonic force field. An empirical anharmonic force field based on the ab initio results is obtained using available experimental vibration–rotation data. Four of the six harmonic and six of the ten cubic force constants have been determined experimentally, the remaining values being fixed at the ab initio values. A good fit to the experimental vibration–rotation data of four isotopic species is obtained.
Electronic properties of CuS: Experimental determination of the magnetic hyperfine interactions and permanent electric dipole moment
Authors: Steimle Timothy C. , Chang Wen-Lie , Nachman David F. , Brown John M.
Published: July 2002

The technique of intermodulated fluorescence has been utilized to record the sub-Doppler optical spectrum of gas-phase copper monosulfide, CuS. The magnetic hyperfine interactions in the A 2Σ−(v=0) and X 2Πi(v=0) states have been analyzed and the permanent electric dipole moment for the X 2Πi state determined. The results have been compared with theoretical predictions and with those for CuO. The magnetic hyperfine parameters are significantly different from those of CuO whereas the dipole moment is nearly identical and these trends are consistent with the decrease in electronegativity of S compared to O.
Observation of correlation effects in zero kinetic energy electron spectra near the N1s and C1s thresholds in N2, CO, C6H6, and C2H4
Authors: Medhurst L. J. , Ferrett T. A. , Heimann P. A. , Lindle D. W. , Liu S. H. , Shirley D. A.
Published: July 2002

Zero kinetic energy (ZKE) spectra of N2, CO, C2H4, and C6H6 were taken across the N1s (N2) and C1s ionization thresholds. Discrete resonances at subthreshold photon energies were observed and were found to become more intense as threshold is approached relative to the same peaks in absorption spectra. For N2 the satellite/main line branching ratios at threshold are: 11(1)% for the 419.7(1) eV binding energy satellite, and 2.3(1.0)% for the 426.5(1) eV binding energy satellite. For CO, the branching ratio for the 304.6(1) eV binding energy satellite is 15(2)% at its threshold. Branching ratios at threshold are also determined for the satellites of C6H6 and C2H4. Decay characteristics and assignments of the continuum features of C6H6 and C2H4 are also discussed.
Calculation of vibration–rotation spectra for rare gas–HCl complexes
Authors: Clary David C. , Nesbitt David J.
Published: July 2002

Calculations are described of spectra for the excitation of the bending and stretching vibrational–rotational energy levels in the van der Waals complexes of HCl with the rare gases Ne, Ar, Kr, and Xe. The calculations are performed using a basis set method, with distributed Gaussian functions being employed for the coordinate associated with the stretching of the rare gas atom. Intensities of combination and fundamental transitions for each of the low frequency modes are calculated for total angular momentum up to J=25. Surprisingly large intensities are predicted for transitions to states with multiple vibrations excited in the bending mode. Promising comparisons are obtained with infrared spectra measured recently for the complexes of HCl with Ne and Ar at low temperatures.
Observation and analysis of the ν3 band of NH+3
Authors: Bawendi M. G. , Rehfuss B. D. , Dinelli B. M. , Okumura M. , Oka T.
Published: July 2002

The ν3 degenerate vibration–rotation band of the ammonia cation NH+3 was observed and analyzed. The spectrum was detected in direct absorption using a tunable difference frequency spectrometer combined with velocity modulation. The ion was produced in a 6 kHz ac discharge with a gas mixture of He:H2:NH3 (∼250:8:1) and with a total pressure of ∼6 Torr. Spin–rotation splittings for most Q-branch transitions were well resolved and spin–rotation interaction constants were determined. A symmetric rotor Hamiltonian with A1–A2 splittings and l resonance was used to analyze the spectrum. The spectral pattern indicates that NH+3 is a planar molecular with D3h symmetry, consistent with a 2A″2 ground electronic state.
Valence ionization and the electron affinities of the open and cyclic forms of Se3 and Te3
Authors: von Niessen W. , Cederbaum L. S. , Tarantelli F.
Published: July 2002

Se3 and Te3 exist as the S3 molecule in an open C2v and a closed D3h form with different electronic configurations but nearly the same total energy. The ionization spectra of Se3 and Te3 are calculated in both the C2v and D3h forms by many-body Green’s function methods. The D3h forms behave quite regularly, but very strong correlation effects are found in the C2v forms. If a theory accurate to third order is used, satellite lines appear at the ionization threshold. If higher order terms are included the satellite lines at the ionization threshold experience a slight change in energy, but a considerable reduction of intensity. Se3 has a positive electron affinity in both the C2v and D3h forms (2B1, 2A′2, states), and Te3 appears to have two positive electron affinities (2B1, 2A1 for the C2v form and 2A2 and 2E′ for the D3h form).
Two-photon excitation of NaI with femtosecond laser pulses
Authors: Engel Volker , Metiu Horia
Published: July 2002

We have performed a quantum analysis of the two-pulse excitation of NaI, pertinent to the experiments of Rosker, Rose, and Zewail. The model for the NaI molecule is based on early work by Faist, Levine, Grice, and Herschbach. The quantum calculation uses a time-dependent fast Fourier transform method and is exact. We examine the dependence of the laser-induced fluorescence (LIF) signal on the properties of pump and probe pulses and on the dynamics of the excited molecule. Several important differences between the LIF method with ultrashort pulses and the cw case are pointed out.
Spectra in the chaotic region: A classical analysis for the sodium trimer
Authors: Gomez Llorente Jose M. , Taylor Howard S.
Published: July 2002

Classical mechanics is used to compute the low resolution spectrum of Na3 in the chaotic regime. The regularity in the spectrum is shown to be due to a family of C2v symmetry tori involving a high amplitude breathing mode and a high amplitude bending mode. These tori are the two mode survivors of the three mode tori whose quantization gives the four assignable lower energy vibrational levels.
Recurrences in the autocorrelation function governing the ultraviolet absorption spectra of O3
Authors: Johnson Bruce R. , Kinsey James L.
Published: July 2002

The approximate dipole–dipole autocorrelation function corresponding to UV photoabsorption in the Huggins and Hartley bands of ozone is obtained by Fourier transformation of the T=195 K data measured by Freeman, Yoshino, Esmond, and Parkinson [Planet. Space Sci. 32, 239 (1984)]. Weak structure seen at vibrational resolution in the broad absorption bands, previously unassigned, is shown to correspond predominantly to 4–5 small recurrent features in the autocorrelation function during the first 130 fs. These time-dependent features are each assigned to particular types of unstable periodic or nearly periodic orbits in the classical dynamics.
Core-electron excitations and the electronic decay of core-to-bound-state transitions in condensed azabenzenes
Authors: Dudde R. , Rocco M. L. M. , Koch E. E. , Bernstorff S. , Eberhardt W.
Published: July 2002

We have measured N 1s near edge absorption spectra and the kinetic energy distribution of electrons emitted in the decay of N 1s core-to-bound-state excitations in condensed pyridine, pyrazine, and s-triazine. The electron emission spectra generated in the electronic decay of the core to bound state resonances lead to singly charged, participator-type molecular final states, equivalent to the final states populated in photoemission, as well as to double hole (Auger) spectator-type final states screened by the presence of a π spectator electron. The deexcitation spectra, therefore, give insight into charge–transfer and screening processes in the initial core-electron excited state, as well as in the final spectator double-hole states. One of the most prominent participator features observed in the spectra of pyridine, pyrazine, and s-triazine is due to the emission of the most strongly bound π electrons, reflecting the dynamic screening of the core hole in the aromatic azabenzene molecules. The spectator states, on the other hand, exhibit a much reduced screening energy shift compared to linear molecules due to the delocalized nature of the π spectator electron.
Electronic excitation transfer in a mixed dimer of p-xylene and p-difluorobenzene
Authors: Lahmani F. , Lardeux-Dedonder C. , Zehnacker-Rentien A.
Published: July 2002

The fluorescence excitation and dispersed fluorescence spectra of a mixed dimer of p-difluorobenzene (pdf) and p-xylene h10 (px) or p-xylene d10 (pxd) formed in a supersonic expansion have been studied in the spectral region of the monomers origins. The excitation spectrum of pdf–px dimer exhibits two kinds of features, one being red shifted from px000 and the other blue shifted from pdf 000 . Deuteration of the px moiety does not modify the observed shifts of the heterodimer absorptions with respect to each monomer 000 transition, and allows assignment of each absorption to the localized excitation of either the px or the pdf half of the complex. Dispersed fluorescence resulting from the excitation of the p-xylene moiety in the complex (pdf–px* or pdf–pxd*) exhibits two components which may indicate a geometry change in the pdf–px* (or pdf–pxd*) excited complex. Dispersed fluorescence resulting from the excitation of the p-difluorobenzene half of the pdf–px complex (pdf*–px) is similar to that of pdf–px* excited state, i.e., displays the characteristics of p-xylene 00 fluorescence. The pdf*–pxd excited complex fluorescence shows the superposition of the resonance fluorescence from the initially excited level (which is characteristic of the p-difluorobenzene 00 fluorescence) together with the pdf–pxd* emission. These results give evidence that electronic excitation has been transfered within the excited complex from the pdf moiety to the px (pxd) moiety.
Symmetry-adapted perturbation theory calculation of the intra-atomic correlation contribution to the short-range repulsion of helium atoms
Authors: Jankowski P. , Jeziorski B. , Rybak S. , Szalewicz K.
Published: July 2002

The first-order exchange energy in the interaction of two helium atoms is expanded as a double-perturbation series with respect to the Moller–Plesset-type fluctuation potentials for the isolated atoms. The resulting perturbation corrections have been calculated using orbital basis sets of varying size. Results in our largest [7s4p2d1f] basis are compared with an accurate value of the first-order energy computed using Gaussian-type geminals. It is shown that the Moller–Plesset-type expansion for the exchange repulsion energy converges moderately fast and that the major part of the intra-atomic correlation correction to the first-order exchange energy is due to one-particle correlation effects included in the Brueckner orbitals.
Orientational order in lipid monolayers: A one-dimensional model
Authors: Kreer M. , Kremer K. , Binder K.
Published: July 2002

Lipid monolayers at low temperatures and large spreading pressure exhibit long-range translational order and the hydrophobic alkane chains of the lipid molecules are then stretched out in an all-trans configuration. The orientational order of the remaining rotational degree of freedom of these alkane chains is studied by means of Monte Carlo and molecular dynamics simulations as well as analytical calculations, but considering a one-dimensional rather than a two-dimensional model. Depending on the interactions among the chains, the ground state of the model is either a ‘‘uniformly tilted’’ state (all chains are tilted by an average angle +θ̄ or −θ̄ relative to the direction perpendicular to the lattice direction) or a ‘‘no-tilt’’ state (θ̄=0). At nonzero temperature, the uniform tilt state disorders by soliton-like kink–antikink excitations, in addition to phonon-like excitations, which exist also in the no-tilt state. In the continuum limit the treatment can be related to the Krumhansl–Schrieffer theory of the one-dimensional φ4 model. However, the quantitative predictions of the latter are in pronounced disagreement with the numerical results, in the temperature regime investigated. By our Monte Carlo techniques, we are able to study the orientational correlation function over the full temperature range, except extremely low temperatures. It is shown that for this model and temperature range the molecular dynamics technique requires much more computer time in order to obtain similarly reliable results than our discretized Monte Carlo approach.
Diffusion Monte Carlo simulations of hydrogen fluoride dimers
Authors: Sun Huai , Watts R. O.
Published: July 2002

The diffusion Monte Carlo method is used to simulate vibrational states for HF and DF monomers and dimers. Ground state energies, dissociation energies, and vibrational motions are discussed on the basis of the simulations. Vibrational frequencies for the dimer are calculated using a mean field, local mode analysis, local mode variational calculations, and direct excited state diffusion Monte Carlo simulations. A tunneling splitting calculation is done using a fixed node simulation. Three different potential surfaces are used for the calculations and results are compared with the available experimental data. One of the surfaces is modified on the basis of the calculations to give improved agreement with experiment.
High orbital angular momentum states in H2 and D2. III. Singlet–triplet splittings, energy levels, and ionization potentials
Authors: Jungen Ch. , Dabrowski I. , Herzberg G. , Vervloet M.
Published: July 2002

The 5g–4 f Rydberg groups of H2 and D2 first studied in paper I have been obtained with a tenfold increase in resolution which made it possible to resolve the singlet from the triplet components. As a result we can now establish separately precise values for the energy levels in the triplet and singlet systems. For this purpose we have remeasured a number of transitions between the lower energy levels for which at present only old measurements are available. In particular we obtain accurate values for the energies of the lowest (stable) triplet state a3Σ+g relative to the singlet ground state, as well as of the ionization potential. The values obtained for the former are more accurate than obtained from singlet–triplet anticrossings while the latter are of similar accuracy as those reported recently by McCormack et al. [Phys. Rev. A 39, 2260 (1989)] and fit well within this accuracy with the most recent ab initio values.
Rotationally specific mode–to–mode vibrational energy transfer in D2CO/D2CO collisions. I. Spectroscopic aspects
Authors: Bewick C. P. , Orr B. J.
Published: July 2002

Time-resolved infrared-ultraviolet double-resonance (IRUVDR) spectroscopy is used to look for rotationally specific channels in collision-induced vibrational energy transfer between the ν6 and ν4 modes of D2CO. The efficiency of such V-V transfer has been shown in previous work to be enhanced by a combination of Coriolis coupling and rotor asymmetry. IRUVDR spectra, recorded in pure D2CO vapor with a range of delay intervals between IR pump and UV probe laser pulses, reveal (J,Ka) -dependent propensities in the resulting ν6→ν4 transfer arising from D2CO/D2CO collisions. At the same time, rotational relaxation within the rovibrational manifold (v6=1) initially prepared by the IR pump laser is found to be more pronounced than the growth of population in the neighboring v4=1 manifold, due to ν6→ν4 transfer. This trend is shown to be reversed in the case of D2CO/N2O collisions, where the effects of rotational relaxation appear to be less pronounced than those of ν6→ν4 transfer. This work, performed with spectroscopic resolution superior to that in previous investigations, has demonstrated a number of new effects, including the identification of weakly allowed t-type (ΔKa=3) features in the IRUVDR spectra. It also provides the spectroscopic background to paper II of this series, which explores the detailed kinetics of (J,Ka) -resolved ν6→ν4 transfer in D2CO.
Molecular dynamics simulation of the effects of temperature on a dense monolayer of long-chain molecules
Authors: Hautman Joseph , Klein Michael L.
Published: July 2002

Molecular dynamics calculations have been used to study the effects of temperature on a dense monolayer of hydrocarbon molecules. The simulation system consisted of 90 flexible chains with headgroups and had periodic boundary conditions in the plane of the surface. The interaction potentials were chosen to model a monolayer of chemisorbed alkyl thiol molecules [S(CH2)15CH3] on a Au(111) surface; molecules that self-assemble from solution to form a triangular lattice at a fixed surface density of 21.4 Å2 per chain. Simulations at different temperatures reveal distinct phases with different kinds of disorder. Nonequilibrium molecular dynamics techniques have been used to investigate the transition from the high-temperature state, in which the molecular planes undergo reorientational motion, to a low-temperature, orientationally ordered state. Possible correlations between the rotational phase transition and the appearance of conformational defects are also explored.
Infrared spectra of the H2–N2 and H2–CO van der Waals complexes
Authors: McKellar A. R. W.
Published: July 2002

Spectra of the weakly bound van der Waals complexes H2–N2 and H2–CO have been studied in the mid- and far-infrared regions corresponding to H2 vibrational and pure rotational frequencies, respectively. The experiments were done using a Fourier transform infrared spectrometer to study equilibrium gas samples at low temperature (77 K) with a long absorption path. The spectra of the complexes appear as fine structure located near the peaks of the lines in the collision-induced spectrum of hydrogen. Compared to earlier studies of these species, the present results have more complete coverage of the various possible transitions, better resolution, and better signal to noise. New structure is reported which corresponds to hindered rotational transitions of the N2 component of an H2–N2 complex and is reminiscent of patterns observed for the N2–Ar and (N2)2 complexes. The relation of these results to far-infrared measurements of Saturn’s satellite Titan, made by the Voyager spacecraft, is discussed.
Symmetry breaking in the NO2 σ radical: Construction of the 2A1 and 2B2 states with C
s symmetry complete active space self-consistent-field wave functions
Authors: Blahous Charles P. , Yates Brian F. , Xie Yaoming , Schaefer Henry F.
Published: July 2002

Jackels and Davidson’s interpretation of the symmetry-breaking problem in the NO2 radical is examined using complete active space self-consistent-field (CASSCF) wave functions. Jackels and Davidson provided a Lewis-structure analysis of the necessary forms of C2v -restricted wave functions for 2B2 NO2. In particular, C2v and single-configuration restrictions force the molecule to ‘‘choose’’ between the beneficial effects of resonance and the adverse effects of inclusion of charged components in the wave function. This choice, according to Jackels and Davidson, results in a distortion to Cs symmetry in the region of the 2B2 minimum. The Cs symmetry complete active space treatment enables NO2 to achieve wave functions of proper symmetry (for both 2A1 and 2B2 states, when C2v nuclear symmetry is present) while simultaneously yielding significantly localized orbitals, thus offering a means to verify the earlier analysis. Although the Cs complete active space results contradict one important Jackels–Davidson result by predicting a very shallow C2v 2B2 energy minimum for NO2, the authors find the earlier molecular orbital picture of NO2 to be a useful tool for qualitatively understanding its electronic structure.