bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hindered internal rotation and o
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o-H2 enrichment in t
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s-stilbene–H2/D2 complexes
Authors: DeHaan David O. , Zwier Timothy S. 
Published: July 2002

A supersonic free jet expansion has been used to prepare trans-stilbene–H2 and D2 complexes. The cooling in the jet collapses most of the ortho and para H2 and D2 rotational population to the lowest rotational levels of a given nuclear spin symmetry: j=0 and j=1. The laser-induced fluorescence excitation spectrum of stilbene–D2 shows a well-resolved doublet at the origin due to stilbene–D2( j=0) and stilbene–D2( j=1) complexes. The 4.9 cm−1 splitting of these transitions indicates that the D2 molecule is undergoing hindered internal rotation in the complex and that the barrier to internal rotation changes upon electronic excitation. The relative intensities of the stilbene–D2( j=0) and stilbene–D2( j=1) origins depend on the D2 concentration in the jet. At low D2 flows the transitions arising from stilbene–D2( j=1) are favored while at high D2 flows the ( j=0)/(j=1) transition intensities approach the 2:1 intensity ratio given by their nuclear spin statistical weights. By contrast, in stilbene–H2 we observe only a single transition at the origin which we assign to stilbene–H2( j=1). We are able to place an upper bound on the stilbene–H2( j=0) transition intensity of 5% of the stilbene–H2( j=1) intensity. Dispersed fluorescence spectra are used to bracket the binding energies of the stilbene–H2/D2 complexes in both ground and excited states. In the ground state of stilbene–H2( j=1) and stilbene–D2( j=0,1) complexes, 169≤D′0 ≤249 cm−1, so that the stilbene–H2( j=0) transitions cannot be missing by virture of the complex being unbound. We propose a simple kinetic scheme which supports the possibility that selective exchange reactions, in which more strongly bound H2( j=1) preferentially displaces H2( j=0) from stilbene, contribute to the enrichment of stilbene–H2( j=1) complexes in the jet. We also propose that H2( j=2) molecules may contribute to the suppression of stilbene–H2( j=0) complexes by virture of the fact that
the H2( j=2) level is above the dissociation threshold for the stilbene–H2 complex while the D2( j=2) level is likely not.
Coupled-cluster calculations on the C2 molecule and the C+2 and C−2 molecular ions
Authors: Watts John D. , Bartlett Rodney J. 
Published: July 2002

Coupled-cluster methods including effects of triple excitations have been used with large basis sets to study several electronic states of C2, C−2, and C+2. re, ωe, De, and Te have been computed for each state considered. For those states for which experimental data are available, the errors are typically less than 0.002 Å, 20 cm−1, and 0.1 eV for re, ωe, and De, respectively. These errors are comparable with the best previous results on C2 and significantly smaller than those for previous calculations on C−2 and C+2. For Te the results are also satisfactory and comparable with previous work, but some difficulties arise when one or both of the states have considerable multireference character. For two states of C+2 not experimentally characterized, the present data should be sufficiently accurate to be of some assistance to experimental studies.
The electron affinity of the ground state of C2 and the ionization potentials of the ground and first excited states of C2 have been computed, and particular attention has been given to correlation errors in these quantities. It has been shown that triple excitations significantly decrease the electron affinity. By neglecting or taking insufficient account of triple excitations, some previous calculations were biased towards the anion and obtained fortuitously good agreement with experiment. The correlation error of the present calculations is such that the calculations are slightly biased towards the neutral molecule, but the error is only 0.2 eV. For the ionization potentials, too, triple excitations play an important role. Reasonable agreement with experiment has been achieved by the present calculations. Overall, the present study: (1) underscores the importance of triple excitations; (2) shows the success of single-reference coupled-cluster theory in calculating properties of a single state, even when that state has considerable multireference character; and (3) highlights the care which must be taken when comparing different electronic states with these methods when one or both states have considerable multireference character.
Absolute state-selected and state-to-state total cross sections for the Ar+(2P3/2,1/2)+CO2 reactions
Authors: Flesch G. D. , Ng C. Y. 
Published: July 2002

Absolute spin–orbit state-selected total cross sections for the reactions, Ar+(2P3/2,1/2)+CO2→CO+2+Ar [reaction (1)], CO++O+Ar [reaction (2)], O++CO+Ar [reaction (3)], C++2O+Ar [reaction (4)], ArC++2O [reaction (5)], ArO++CO [reaction (6)], and ArCO++O [reaction (7)] have been measured in the center-of-mass collision energy (Ec.m.) range of 0.26–131 eV. The ratio of the charge-transfer cross section due to Ar+(2P1/2) to that associated with Ar+(2P3/2) varies in the range of 0.5–0.8. The appearance energies observed for CO+ (Ec.m.=4.2±0.5 eV), O+ (Ec.m.=3.7±0.5 eV), and C+ (Ec.m.=12.6±0.5 eV) are in agreement with the thermochemical thresholds for reactions (2), (3), and (4), respectively. The comparison of the absolute cross sections for CO+, O+, and C+ from CO2 by photoionization and by dissociative charge transfer [reactions (2)–(4)] is made. The kinetic-energy analysis of product CO+2, CO+, O+, C+, ArO+, and ArC+ suggests that reactions (2)–(7) proceed via a charge-transfer predissociation mechanism. This experiment, together with the previous studies of Ar+(2P3/2,1/2)+N2(O2,CO), supports the conclusion that product ions formed by dissociative photoionization are also produced by dissociative charge transfer. We find that the absolute cross sections for product ions formed in the dissociative charge-transfer processes [reactions (2)–(4)] are substantially greater than those formed in the dissociative photoionization of CO2, a finding consistent with the general observation that photoionization cross sections are significantly smaller than charge-transfer cross sections.
The relative cross sections for CO+, O+, and C+ formed by reactions (2)–(4) are also found to be different from those for photoionization of CO2. This difference is attributed to the anisotropic interaction potential surface responsible for the Ar+(2P3/2,1/2)+CO2 reactions.
Rovibronic interactions in NO2 around 17 700 cm−1 observed by Zeeman effect and anticrossing experiments
Authors: Delon Antoine , Dupre Patrick , Jost Rémy 
Published: July 2002

We have observed the Zeeman effect on N=1, K=0 rotational levels of seven vibronic levels of NO2 located between 17 438 and 17 842 cm−1. We have used a supersonic jet, (Trot≊4 K) located inside a 5 MW Bitter coil of 100 mm bore which allows magnetic field scans up to 8 T. CW monomode ring dye laser excitation allows a resolution of about 300 MHz limited by the residual Doppler effect. We have observed the evolution of the Zeeman energy levels versus the field. The values of high field Landé factors range from 1.80 to 1.98, significantly lower than the free spin value (2.0023). The standard perturbation theory of Curl [Mol. Phys. 9, 585 (1965)], which relates Landé factor and the spin-splitting constant ε̄, does not fit the observed results. In addition, 54 anticrossings due to rovibronic interactions have been observed. The corresponding matrix elements range from about 50 MHz (limited by field inhomogeneities) up to 15 GHz, (0.5 cm−1). The expected number of anticrossings in the magnetic field range scanned (from the known rovibronic density of state and from first-order ‘‘spin–rotation’’ interaction selection rules), is only 27. We explain the additional anticrossings by higher order interactions. In fact, the distribution of observed matrix elements is smooth, without any gap between first order and higher order matrix elements. In this case, we have assumed that the first order matrix elements are the larger ones.
With this assumption, we have determined the average reduced matrix element of first-order spin–rotation interaction: 0.73±0.15 cm−1. These off diagonal spin–rotation interactions are expected to be roughly independent of the N rotational quantum number. This contrasts with the diagonal electronic-spin interactions (spin splittings) which increase linearly with N but which are significantly weaker than off-diagonal interactions at least for the N=1, K=0 levels studied here. We show that these rovibronic interactions (by both first order and higher order) induce the numerous irregularities previously observed in the zero field jet cooled excitation spectrum of NO2. Moreover, the average reduced matrix element of first order spin–rotation interaction observed in the zero field spectrum from 16 500 to 18 500 cm−1 is about 0.76±0.25 cm−1 in agreement with the above-mentioned high field measurement.
Fluctuations in absorption spectra and final product state distributions following photodissociation processes
Authors: von Dirke Michael , Heumann Bernd , Kühl Klaus , Schröder Thomas , Schinke Reinhard 
Published: July 2002

We present a quantum mechanical wave packet study for the unimolecular dissociation of a triatomic molecule into an atom and a diatom. The 3D potential energy surface used in the dynamics calculations is that of the B̃ state of water corresponding to the second absorption band. Both OH stretching coordinates and the bending angle are included. What is not taken into account is the strong nonadiabatic coupling to the lower-lying Ã and X̃ states which in reality drastically shortens the lifetime in the B̃ state. For this reason the present study is not a realistic account of the dissociation dynamics of water in the 122 nm band. It is, however, a representational investigation of a unimolecular reaction evolving on a realistic potential energy surface without barrier. The main focus is the resonance structure of the absorption spectrum and the final rotational state distributions of the OH fragment. The total absorption spectrum as well as the partial dissociation cross sections for individual rotational states of OH show drastic fluctuations caused by overlapping resonances. The widths of the individual resonances increase, on average, with the excess energy which has the consequence that the cross sections become gradually smoother. Although the low-energy part of the spectrum is rather irregular, it shows ‘‘clumps’’ of resonances with an uniform spacing of ∼0.1 eV. They are discussed in the context of IVR and a particular unstable periodic orbit. In accordance with the fluctuations in the partial dissociation cross sections as functions of the excess energy the final rotational state distributions show pronounced, randomlike fluctuations which are extremely sensitive on the energy.
The average is given by the statistical limit (PST), in which all levels are populated with equal probability. With increasing excess energy the distributions more and more exhibit dynamical features which are reminiscent of direct dissociation like rainbows and associated interferences. Classical trajectories for small excess energies are chaotic, as tested by means of the rotational excitation function, but become gradually more regular with increasing energy. Our wave packet calculations hence demonstrate how the transition from the chaotic to the regular regime shows up in a fully quantum mechanical treatment. The results of the present investigation are in qualitative accord with recent measurements for the unimolecular dissociation of NO2.
Stimulated emission pumping spectroscopy via two-color resonant four-wave mixing
Authors: Williams Skip , Tobiason Joseph D. , Dunlop James R. , Rohlfing Eric A. 
Published: July 2002

We present a combined theoretical and experimental study of the application of two-color resonant four-wave mixing (RFWM) to stimulated emission pumping (SEP) spectroscopy. The theoretical approach employs time-independent, diagrammatic perturbation theory and a spherical tensor analysis in an extension of a recent treatment of degenerate four-wave mixing [Williams, Zare, and Rahn, J. Chem. Phys. 101, 1072 (1994)]. The resulting signal expression for two-color RFWM separates the molecular properties from purely laboratory-frame factors determined by the polarizations of the input beams and the rotational branch types of the SEP PUMP and DUMP transitions. This expression is valid in the limit of weak fields and for molecules in which the total angular momentum (omitting nuclear spin) is a good quantum number. In addition, we demonstrate that the spectral response for tuning the DUMP laser is a simple Lorentzian in free-jet experiments. We test our theoretical results and demonstrate the applicability of RFWM-SEP to jet-cooled, transient species in experiments on C3 and HCO. Using the well-studied Ã 1Πu–X̃ 1Σ+g system of C3, we illustrate and compare the two possible schemes for RFWM-SEP. These are defined as ω1=ω2 (PUMP) and ω3=ω4 (DUMP) or ω1=ω4 (PUMP) and ω2=ω3 (DUMP), where ω1, ω2, and ω3 are the input frequencies and ω4 is the signal frequency.
Using the B̃ 2A′–X̃ 2A′ system of HCO, we obtain RFWM-SEP spectra that probe ground-state vibrational resonances lying above the low threshold for dissociation to H+CO. Varying the polarization of the input beams or PUMP rotational branch produce dramatic effects in the relative intensities of rotational lines in the RFWM-SEP spectra of HCO; these effects are well-described by our theoretical analysis. Finally, RFWM-SEP spectra of HCO resonances that are homogeneously broadened by dissociation are consistent with the theoretically predicted Lorentzian line shape; the full widths for these levels are in good agreement with those determined via unsaturated fluorescence depletion SEP.
A field theory of random heteropolymers near solid surfaces: Analysis of interfacial organization and adsorption–desorption phase diagram
Authors: Gutman Lorin , Chakraborty Arup K. 
Published: July 2002

Understanding the interfacial organization of heteropolymers near solid surfaces is an issue of fundamental interest that is relevant for many technological and biological applications. In this paper we address several questions pertaining to the surface-induced ordering and the adsorption–desorption phase behavior of a dilute solution of two-letter random heteropolymers interacting with a solid surface. Our analysis is based on a statistical field theoretic formulation of the propagator for the problem of interest. We employ the replica trick to alleviate analytical difficulties which arise when considering averaging over the sequence distribution of the A and the B units. In order to highlight the effects of the surface, we consider the situation wherein the intersegment interactions are of the excluded volume type while the segment–surface interactions of the A and B segments are arbitrarily different. Within the replica symmetric solution, we show that proper coarse-graining of the interaction potentials leads to exact analytical expressions for the self-consistent propagator of the heteropolymer at theta conditions and for the case where excluded volume interactions prevail. One of our interesting findings is that heteropolymers undergo an adsorption–desorption transition in the vicinity of a surface that interacts with the different types of segments in arbitrarily different ways. This is consistent with our previous numerical findings for much more restricted circumstances.
We explicitly analyze the influence of the fluctuations in the sequence distribution on the conformational organization of the adsorbed chains and obtain the scaling behavior of properties of interest in the vicinity of the adsorption–desorption threshold with respect to the disorder strength and other polymer interaction parameters. Specifically, invoking the Ehrenfest theorem we find that the adsorption–desorption transition at theta conditions is a second-order phase transition while in the case where excluded volume interaction prevails the transition becomes first order. We also obtain exact analytical expressions for the adsorption–desorption threshold. The threshold exhibits quite an unusual dependence on the strength of the disorder. Finally, we compute the point of onset of repulsive forces between plates that confine a random copolymer solution as a function of chain sequence distribution. We suggest specific experiments employing the surface force apparatus that could directly test our predictions.
Random matrix treatment of intramolecular vibrational redistribution. II. Coriolis interactions in 1-butyne and ethanol
Authors: Go Jungsug , Perry David S. 
Published: July 2002

A random matrix methodology has been applied to simulate the molecular eigenstate resolved infrared spectra of the 1-butyne ν16 band and the ethanol ν14 band. In these methyl C–H stretch bands, each rotational transition is fragmented into a clump of molecular eigenstates. The frequencies and intensities of these discrete features carry information about the rate and mechanism of the intramolecular vibrational redistribution (IVR) which would follow the coherent excitation of the zero-order state. The simulations include anharmonic and Coriolis x-, y-, and z-type interactions. These interactions mix the bright state with the bath and also mix the bath states with each other. Since the vibrational identities of the bath states are assumed to be sufficiently mixed, the vibrational parts of the coupling matrix elements are treated stochastically following the development in Paper I of this series [J. Chem. Phys. 98, 6665 (1993)]. The rotational parts of the matrix elements are treated dynamically based on the known rotational quantum number dependence of the Coriolis effect. A stochastic treatment cannot expect to reproduce the detailed line positions and intensities of the experimental spectra, therefore three measures of IVR are used as the basis for comparison of the simulation with experiment.
The measures are the dilution factor φd, the interaction width Δε, and the effective level density ρeffc. In the presence of multiple coupling mechanisms (near the best fit to the ethanol ν14 band), the correlations between φd and Δε and the bright-bath Coriolis coupling mechanisms follow the expected trends. It was also found that ρeffc is sensitive to the x, y Coriolis coupling among the bath states. The results were not sensitive to the z-type Coriolis coupling among the bath states in the region of the ethanol simulation, but ρeffc was sensitive to it in the simulation of the 1-butyne ν16 band. Best-fit coupling parameters were obtained for both simulated bands. The rms bright-bath z-type Coriolis coupling was found to be 0.028±0.005 cm−1 which is about three times the value obtained from a naive approach which neglects the interaction of the multiple coupling mechanisms. A direct count vibrational level density, ρvib, provided good agreement with the experiments when a full treatment of the torsional modes was included and a 20% enhancement of the density from neglected diagonal anharmonicities was added. A method of quantifying the conservation of the rotational quantum number, K, is provided by the inequalities, ρvib≤ρeffc≤(2J+1)ρvib. For 1-butyne, ρeffc is closer to ρvib than for ethanol indicating that K is more nearly conserved. While this work treats only anharmonic and Coriolis coupling, the random matrix formalism provides the ability to treat a wide variety of coupling schemes.
A physical model for merging in two-dimensional decaying turbulence
Authors: Riccardi G. , Piva R. , Benzi R. 
Published: July 2002

Some aspects of the simulation by point vortices of two-dimensional decaying turbulence are discussed, together with their most relevant consequences for the decay of the number of vortices. Two different merging models are proposed to simulate dissipative interactions between corotating vorticity structures within a point vortex simulation. Both models are based on a statistical approach to assign the number of vortices resulting from the merging of two vortices of different size. Probability distributions are defined for the production of one, two, or three vortices, and they are assigned as functions of the circulation ratio for the two interacting vortices. These functions are determined by performing a large number of Contour Dynamics simulations of vortex interactions, each under a given strain field. A simple rule to reset the vorticity field, at the end of the merging process, is discussed in terms of conserved quantities for the formation of one or three vortices. To complete the merging model, a criterion that indicates the onset of a merging event between two close vortices of like sign is required. The first model is defined by adopting a critical distance as merging criterion. In this way, the effect of the strain on the merging process is taken into account only in a statistical manner, i.e., by the probability law for the merging products. The use of this merging model into a point vortex simulation gives a surprisingly good agreement with the results for the vortex number decay obtained by Dritschel via Contour Surgery.
Nevertheless, a merging criterion based on the critical distance appears questionable, since it disregards the effect of the strain on the merging conditions. To this aim, we introduce a more sophisticated merging model that uses the dynamics of elliptical patches under a given strain field to select the merging events. This second model accounts also directly, and not only in a statistical sense, for the strain influence over the merging conditions, revising thoroughly the critical distance concept. The results show that the vortex number decay is not strongly sensitive to a detailed description of each individual merging process and, if the interest is focused on the vortex number decay, further improvements of the merging model are not strictly required.
Witchcraft, genealogy, Foucault
Authors: Russell Steven 
Published: July 2002

ABSTRACTThis paper is a genealogical reflection on both the historiography of European witchcraft and the dynamics of witchcraft trials. I argue that traditional scholarly assumptions about the ‘unsophisticated’ nature of early modern European mentalities result in inadequate representations of accused witches and of the social contexts and processes of the trials. Genealogy, by contrast, problematizes fundamental notions such as reason, order, power and progress in ways that not only provide a different range of effective tools for the analysis of belief in witchcraft, but also underline its crucial significance for social theory. In the final section, an analysis of a typical trial is undertaken employing key genealogical insights into confession, torture, truth, governmentality, power, pleasure and pain.