bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical selection studies of electronic relaxation from the S1 state of jet-cooled anthracene derivatives
Authors: Amirav Aviv , Horwitz Chanan , Jortner Joshua 
Published: July 2002

In this paper we explore the energy dependence of the interstate electronic relaxation rates knr from the S1 manifold of anthracene and seven of its isotopic and chemical derivatives, which were inferred from quantum yield data. Absolute fluorescence quantum yields Y from groups of rotational states within the electronic origin S1(0) and from vibrational states were obtained over the excess energy Ev=0–3000 cm−1 above S1(0) by the simultaneous interrogation of the fluorescence excitation spectra and of the absorption spectra in seeded, pulsed, planar supersonic jets of Ar. Additional information was obtained from quantum yield data of van der Waals (vdW) complexes of these molecules with Ar. The fluorescence quantum yields from the S1(0) of anthracene, 9-cyano-anthracene, and 9,10-dibromoanthracene were found to be independent of the rotational state, providing further evidence for the rotational independence of knr from a single doorway state. From the Y data of the electronic origins and from the Ev dependence of Y we conclude that intersystem crossing (ISC) dynamics of the S1 manifold is dominated by the interplay between two classes of nonreactive coupling and/or relaxation: (i) Interstate coupling, involving the superposition of direct S1→(T1) ISC together with S1→(Tx) →(T1) mediated ISC through a sparse or dense (Tx) manifold of a higher triplet state; (ii) Intrastate coupling within the S1 manifold, which sets in with increasing Ev and which results in intramolecular vibrational energy redistribution (IVR) at high Ev. The dominant role of mediated interstate coupling in ISC dynamics from S1(0) and from low Ev states was inferred from the inverse deuterium isotope effect on the ISC rates, the extreme sensitivity of knr of deuterated anthracene to a single H atom substitution, and to level shifts induced by complexing with Ar, as well as from the three-orders-of-magnitude difference between the knr values from the S1(0) of 9-bromoanthracene and of 9,10-dibromoanthracene.
The onset of the mediated ISC is documented by an abrupt drop of Y in the narrow (Ev =617–805 cm−1) energy range for 9,10-dichloroanthracene and by the oscillatory energy dependence of Y vs Ev and the extreme energy sensitivity of Y in the range Ev =157–800 cm−1 of 9,10-dibromoanthracene, which is attributed to near-degeneracies between S1 states and the mediating (Tx) states. These resonance effects can be drastically modified by dispersive level shifts induced by complexing with Ar. At high excess vibrational energies some universal features of the Ev dependence of knr are exhibited. These involve a gradual increase of
k n r with increasing Ev at medium energies (Ev =1000–1800 cm−1), which correspond to the intermediate level structure for intrastate coupling and a very weak Ev dependence of knr at high energies (Ev =1800–3000 cm−1), which manifest the effect of statistical intrastate IVR on interstate ISC.
Semiclassical treatment of the vibrational spectroscopy of OCS
Authors: Aubanel Eric E. , Wardlaw David M. 
Published: July 2002

The utility of a primitive semiclassical method for the quantitative prediction of vibrational eigenvalues and electric dipole transition intensities in triatomic molecules is assessed for the particular case of rotationless OCS in its ground electronic state by comparison to exact quantum calculations. The semiclassical method is based on numerical integration of appropriately selected classical trajectories. The potential energy function determined by Foord, Smith, and Whiffen [Mol. Phys. 29, 1685 (1975)] and the electric dipole moment function determined by Tanaka, Tanaka, and Suzuki [J. Chem. Phys. 82, 2835 (1985)] provide the model of the OCS system. Eigenvalues are obtained by the method of adiabatic switching, the number of trajectories required for this purpose being minimized to four using an extension of Johnson’s Fourier series method [J. Chem. Phys. 83, 1204 (1985)]. The resulting semiclassical vibrational transition frequencies (with respect to the ground state) agree with the corresponding quantum frequencies to within 1 cm−1 (2 cm−1) for 112 (128) of the 145 converged quantum levels, with the largest discrepancy being 5.2 cm−1. The semiclassical frequencies are compared to the experimental results of Fayt [Ann. Soc. Sci. Brux. 86, 61 (1972)] and to the semiclassical results of Colwell [Chem. Phys. 46, 165 (1980)]. The sets of 176 semiclassical and 145 converged quantum transition frequencies reported here are the most extensive and complete to date, the highest energy level being ∼7500 cm−1 above the ground state. The methodology of Wardlaw, Noid, and Marcus [J. Phys. Chem. 88, 536 (1984)] for the determination of semiclassical transition intensities in 2D oscillator systems is herein extended to the vibrational degrees of freedom in triatomic molecules. For numerous transitions from the ground state and from several low-lying excited states, the semiclassical intensities agree with the quantum intensities to within 6% in the absence of resonances in the associated approximate eigentrajectories. When resonances are involved, the primitive semiclassical treatment is found to be far less accurate, as is expected. A
numerical determination of the classical actions, Fourier spectra of the coordinates, surfaces of section, and 2D slices through configuration space are presented for representative resonant and nonresonant approximate eigentrajectories. The inherent uncertainties in the semiclassical energy levels and in the transition intensities (if no resonant trajectories are involved) are found to provide a very reliable upper bound on the difference between the semiclassical and quantum results.
Overtone spectroscopy of propyne and propyne-d1
Authors: Baylor Lewis C. , Weitz Eric , Hofmann P. 
Published: July 2002

The vibrational overtone spectra of the acetylenic and methyl C–H stretches of propyne were obtained for the v=1 to v=6 and v=1 to v=7 levels, respectively. Propyne-dl was also studied and the methyl C–H stretching overtones were measured from v=1 to the v=7 level. The C–D stretch was observed only in the fundamental and first overtone regions. Lower level overtones were obtained by standard infrared techniques, while higher absorptions (&gt;12 000 cm−1) were obtained by intracavity dye laser photoacoustic spectroscopy. The C–H stretches in both molecules were analyzed in terms of the local-mode model, and harmonic frequencies (ωi) and anharmonicities (Xii) were calculated. In propyne these values were (acetylenic C–H stretch) ω1=3384±5 cm−1 and X11=−50±1 cm−1 and (methyl C–H stretch) ωm =3037±5 cm−1 and Xmm =−65±2 cm−1. In propyne-dl the methyl C–H stretch parameters were ωm =3034±5 cm−1 and Xmm =−64±2 cm−1. For propyne, a hot band (ν9→ν9+vν1) accompanying the acetylenic C–H stretch was observed for v=1–6 and the anharmonic interaction constant (X19=−23±7 cm−1) was calculated. A crossover from normal- to local-mode behavior has been observed for the methyl C–H stretches in propyne and propyne-dl at the v=3 and 4 levels. Below v=3 the symmetric and antisymmetric methyl C–H stretches are designated by the usual normal-mode notation (ν2 and ν6 in propyne; ν1 and ν6 in propyne-dl), while for v≥3 the single observed band is designated as a ‘‘methyl’’ C–H stretch, vνm. Peak absorption cross sections have been measured for Δv1=1–5, Δvm =3–5, Δv2=1 and 2, and the parallel component of 2ν6 in propyne, and for Δv2=1 and 2, Δv1=1 and 2, Δvm =3 and 4, and the parallel component of 2ν6 in propyne-dl. During the course of this work the spectral constants of 3,3,3-trifluoropropyne were redetermined. The harmonic frequency ω1 is 3376±6 cm−1, the anharmonicity
X 1 1 is −49±1 cm−1, and the anharmonic interaction constant X17 is −17±6 cm−1.
Experimental and theoretical total state-selected and state-to-state absolute cross sections. II. The Ar+(2P3/2,1/2)+H2 reaction
Authors: Liao C. -L. , Xu R. , Nourbakhsh S. , Flesch G. D. , Baer M. , Ng C. Y. 
Published: July 2002

Total state-selected and state-to-state absolute cross sections for the reactions Ar+(2P3/2,1/2)+H2(X,v=0)→Ar (1S0)+H+2(X̃,v′) [reaction (1)], ArH++H [reaction (2)], and H++H+Ar [reaction (3)] have been measured in the center-of-mass collision energy Ec.m. range of 0.24–19.1 eV. Absolute spin–orbit state transition total cross sections (σ3/2→1/2,σ1/2→3/2) for the collisions of Ar+(2P3/2,1/2) with H2 at Ec.m.=1.2–19.1 eV have been obtained.
The measured state-selected cross sections for reaction (1) [σ3/2,1/2(H+2)] reveal that at Ec.m.≤5 eV, σ1/2(H+2) is greater than σ3/2(H+2), while the reverse is observed at Ec.m.≥7 eV. The total state-to-state absolute cross sections for reaction (1) (σ3/2,1/2→v′) show unambiguously that in the Ec.m. range of 0.16–3.9 eV the dominant product channel formed in the reaction of Ar+(2P1/2)+H2(X,v=0) is H+2(X̃,v′=2)+Ar. These observations support the conclusion that at low Ec.m. the outcome of charge transfer collisions is governed mostly by the close energy resonance effect. However, at sufficiently high Ec.m.(&gt;6 eV) the charge transfer of Ar+(2P3/2)+H2 is favored compared to that of Ar+(2P1/2)+H2.
The relative values measured for X1/2→v′[≡σ1/2→v′/σ1/2 (H+2)] are in good accord with those predicted from calculations using the state-to-state cross sections for the H+2(X̃,v′=0–4)+Ar charge transfer reaction and the relation based on microscopic reversibility. The experimental values for X3/2→v′[≡σ3/2→v′/σ3/2 (H+2)] and those predicted using the microscopic reversibility argument are also in fair agreement. The spin–orbit effect for the cross section of reaction (2) [σ3/2,1/2(ArH+)] is significantly less than that for reaction (1). Both σ3/2(ArH+) and σ1/2(ArH+) decrease rapidly as Ec.m. is increased, and become essentially identical at Ec.m. ≊3.8 eV. The cross sections for reaction (3) observed in the Ec.m. range of 2.5–12 eV are ≤3% of σ3/2,1/2(H+2).
The onset for the formation of H+ by reaction (3) is consistent with the thermochemical threshold. The values for σ3/2→1/2 and σ1/2→3/2 observed here are nearly a factor of 2 greater than those measured by the energy loss spectroscopic method. However, the kinetic energy dependencies for σ3/2→1/2 and σ1/2→3/2 are in accord with the previous measurements. Theoretical cross sections for the charge transfer and spin–orbit state transition reactions are calculated at Ec.m.=19.3 eV using the nonreactive infinite-order sudden approximation for comparison with experimental values.
Theory of fluorescence excitation spectra using anharmonic-Coriolis coupling in S1 and internal conversion to S. II. Application to the channel three problem in benzene for the 14112 band
Authors: Helman Adam , Marcus R. A. 
Published: July 2002

Rotational lines in the fluorescence excitation spectra of the 14112 band of the first excited singlet state (S1) of benzene are calculated for various J and K. For this purpose, perturbation theory is used to obtain an ‘‘eigenstate’’ in S1. Internal conversion to S0 via Franck–Condon (FC) factors is then calculated. A search procedure is used to obtain the important contributors to this S1 state and to this internal conversion process S1→S0 using the perturbation theory coefficients and the FC factors in the evaluation function. At low J, the calculated lines with K=0 are sharp, other lines being broadened and diminished in intensity. The calculated K=0 lines have a linewidth proportional to J(J+1). For high J, the lines with K=J remain sharp, the other lines being broadened and diminished in intensity. These various results are in general agreement with the experimental findings. The onset of channel three in benzene occurs in the present mechanism via anharmonic-Coriolis coupling in the S1 state plus internal conversion to S0. The calculations suggest that, at low J, parallel Coriolis coupling causes mixing of the in-plane mode-excited ‘‘light state’’ with in-plane modes that are anharmonically coupled to out-of-plane modes.
Dark states with certain excited out-of-plane mode contributions possess large FC factors for the internal conversion to S0. At high J, on the other hand, the in-plane modes are coupled directly to these out-of-plane modes by perpendicular Coriolis coupling. Paths involving two perpendicular Coriolis operators are important at high J in the present calculation—their matrix elements are larger at high J and so they become more competitive relative to purely anharmonic coupling operators. Such two-Coriolis paths at high J are expected to yield multiple excitation in the out-of-plane modes and further enhance the internal conversion. The perpendicular Coriolis coupling is least at J=K and so these lines survive at high J. Two-Coriolis operator paths are calculated to be relatively unimportant at low J. The present calculations, using the same electronic matrix element, account for both the low JK=0 and high JK=J sets of lines being the dominant ones. Aspects regarding further study are discussed.
Microwave spectroscopy and interaction potential of the long-range He...Ar+ ion
Authors: Carrington Alan , Leach Christine A. , Marr Andrew J. , Shaw Andrew M. , Viant Mark R. , Hutson Jeremy M. , Law Mark M. 
Published: July 2002

We have measured and interpreted a microwave spectrum of the HeAr+ ion in which all of the observed energy levels lie within 8 cm−1 of the lowest dissociation limit, He(1S)+Ar+(2P3/2). We use an ion beam technique in which the HeAr+ ions are formed by electron impact, accelerated to kilovolt potentials, and mass-analyzed. After passage through an appropriate section of waveguide, the ions enter an electric field lens in which state-selective fragmentation occurs; the Ar+ ions produced in the lens are separated from all other ions by means of an electrostatic analyser and detected with an electron multiplier. Microwave transitions induced in the waveguide section result in population transfer which produces detected changes in the electric field-induced Ar+ fragment current. Many transitions have also been observed by a microwave–microwave double resonance technique. We have observed 68 lines spanning the frequency range 6–170 GHz; no immediately recognizable pattern is apparent. We have measured the Zeeman splitting produced by a small axial magnetic field for almost every line, which enables us to determine the values of the total angular momentum J involved in each transition, and also effective g factors for the two levels involved. We are therefore able to construct a purely experimental pattern of 37 levels lying within 8 cm−1 of the dissociation limit. The data are treated first by means of a conventional effective Hamiltonian in a case (c) basis, which allows electronic and vibrational quantum numbers to be assigned to most of the levels; the assignments are approximate, however, because very strong rotational-electronic coupling undermines the Born–Oppenheimer approximation.
A more complete theoretical treatment is then presented, using the coupled-channel method in a case (e) representation to calculate the energy levels without making the Born–Oppenheimer approximation. The microwave transition frequencies and g-factors are fitted, together with earlier ultraviolet spectra, to provide a new interaction potential (designated MAL1) for He interacting with Ar+(2P3/2 and 2P1/2). The MAL1 potential is substantially more accurate than previous potentials, especially in the long-range region and for the A1 2Π3/2 state, which had not been observed before. An important new feature of the MAL1 potential is that the long-range C6 coefficient is strongly anisotropic, so that the different electronic curves have substantially different C6 coefficients.
The relationship between q profiles, transport, and sawteeth in tokamaks
Authors: Haas F. A. , Thyagaraja A. 
Published: July 2002

The purpose of this paper is to investigate the possible relationships between transport properties such as thermal diffusivity and resistivity on the one hand, and the magnetic properties such as q profile and toroidal flux change on the other, in tokamaks that exist under macroscopically quasistationary conditions. It is experimentally well established that when the sources are held constant over times long compared with energy and particle confinement times, tokamak discharges can exist in a quasistationary state with or without periodic sawteeth superposed on the basic equilibrium.
The principal aim of this study is to provide qualitative physical insight into the nature of such states. For simplicity, single-fluid equations are assumed and the analysis is restricted to a cylinder model. The complete set of conservation equations comprising continuity, pressure balance, Ohm’s law, and energy balance are used along with appropriate sources. The conductive energy loss is assumed to occur due to an anomalous thermal diffusivity. Following earlier time-dependent studies of tokamak transport phenomenology due to the authors [Haas and Thyagaraja, Plasma Phys. Controlled Fusion 28, 1093 (1986)], the friction force in the generalized Ohm’s law is assumed to be described by an effective resistivity tensor with its principal axes in the poloidal and toroidal directions. The toroidal resistivity is taken to be of order Spitzer while the poloidal component ηθ is assumed to be anomalously large compared with ηz. A range of phenomena involving Ohmic discharges, auxiliary heated discharges, and noninductively driven currents is investigated. Attention is drawn to the joint implications of the conservation laws and the general forms of the constitutive relations for the structure of the profiles and conditions for the existence of equilibria. In particular, it is shown that βp&gt;1 is achievable in macroscopically steady conditions, only if a sufficiently strong particle source is present in addition to an energy source. It also follows from the analysis that low βp discharges require an anomalous thermal force type term in Ohm’s law, in addition to the anomalous poloidal resistivity.
Recent experimental results on sawtoothing discharges are used to extend the theoretical considerations from strictly steady discharges to those involving sawteeth. A simple nonlinear dynamical model of sawtoothing is constructed and used to illustrate some of the features of sawtooth oscillations. The paper is intended to complement fuller numerical studies. It may help in understanding transport and large-scale relaxation processes like the sawtooth in tokamaks by providing a set of theoretical relations that can be subjected to a direct experimental test. It is a feature of the results that they are independent of the details of the turbulent dynamics, which are ultimately thought to be responsible both for the form and scaling of the constitutive properties considered.
Chaotic mixing and heat transfer between confocal ellipses: Experimental and numerical results
Authors: Saatdjian E. , Midoux N. , Gastou Chassaing M. I. , Leprevost J. C. , André J. C. 
Published: July 2002

The annular region between two concentric, confocal ellipses is a new geometry which is particularly effective for either mixing of viscous fluids or heat transfer enhancement in the important limit of a high Péclet number. This geometry is in many respects similar to the annular space between two eccentric, rotating cylinders although it possesses two (instead of one) axes of symmetry. The recently obtained analytical solution of the Stokes flow equations in this geometry shows that at steady state and for counter-rotation of the inner and outer ellipses, two opposite saddle points (connected by two different streamlines) appear in the region of minimum gap. This flow characteristic is also exhibited by the eccentric cylinder system for some cases of co-rotation. The Poincaré sections obtained when the inner and outer ellipses are displaced using a discontinuous velocity protocol show that a more effective long term mixing is obtained for the counter-rotating case, this is confirmed by the experimental data we have obtained. The opposite conclusions (more effective mixing for co-rotation) have been given in the eccentric cylinder geometry.
Photographs of the fluorescent dye after 5 periods are compared with remarkable success to numerical blob deformation experiments. Experimental results also confirm previous results based on an analysis of Poincaré sections. In particular, better mixing is obtained when the inner ellipse displacement per period increases. Finally, this geometry is shown to be particularly effective as a heat exchanger. For steady, counter-rotation of the two boundaries, the recirculation zones can lead to a heat transfer rate increase of 80% over that of pure conduction at high Péclet numbers, and, by an appropriate sinusoidal modulation of the angular velocity of one boundary, the heat transfer rate can be more than double that of pure conduction. Since an analysis of the experimental data also suggests that the mixing rate for a sinusoidal modulation of the angular velocity of the boundaries is better than for a discontinuous velocity protocol, we propose that the average Nusselt number per period could be one of the several useful tools in the global optimization of the mixing protocol.
Attention‐deficit/hyperactivity disorder in the drug and alcohol clinic
Authors: Tucker Peter 
Published: July 2002

AbstractAttention‐deficit/hyperactivity disorder (ADHD), a disorder generally seen in children but more recently found in many cases to persist to adulthood, has been found to be associated with later development of substance abuse. The author reviews evidence for this, and for the possible mediating role of antisocial behaviour in this association. It is concluded that the latter may have a predominating role, but that in any case there is likely to be a significant number of adults with ADHD in substance‐abusing populations. It is doubtful that such individuals are truly self‐medicating their psychiatric disorder. Suggestions are made regarding an approach to this problem of dual diagnosis.
Regional culture in post-war Friuli: Literature in dialect, nationalism and friulanità
Authors: Johnson John R. L. 
Published: July 2002

SummaryThe unprecedented increase in literary production in Friuli in the post-war period has coincided with the rise of popular ethno-nationalism in the region. Although there is an evident connection between the political, social and cultural fields in Friuli, this relationship is both complex and full of potential conflicts. This paper provides a brief overview of Friulian regionalism, before considering the specific role assigned to literature in Friulian by proponents of regional autonomy. It examines the problematic nature of the dominant ideology of friulanità and discusses the responses of a number of authors to the prevailing themes of cultural discourse in the region. In conclusion, it examines the ideological conflicts caused by modernisation in the region, and considers the impact that the transformation of the region has had on the literary debate, concentrating on the difficulties caused by Friulian linguistic purism.