Cusp satellite bands in the spectrum of molecule

We report measurements and a theoretical explanation of the cusp-shaped satellite bands in the blue wing of the cesium D₂ resonance line which have been observed for the first time. The bands are identified as transitions where the upper state dissociates into the 6 ²P _3/2 + 6 ² S _1/2 atomic asymptote. The experiment has been performed using a standard absorption setup, computer controlled data acquisition and computer data processing. We have shown that the peculiar shape of the difference-potential curve is solely responsible for the spectrum containing the cusp-shaped satellite bands. The appearance of these satellite bands has been discussed and explained relating the theory of satellite bands to the catastrophe theory. The shape of the line wing and of the satellite bands have been calculated using the Fourier transform technique. To ensure a more stringent comparison between the experimental and the theoretical spectrum, we have analyzed and compared the derivatives of the measured and the calculated satellite band shape. On the contrary to the customary direct comparison between the measured and the calculated absorption coefficient, the derivative clearly shows all differences and resemblances between satellite band profiles. The degree of coincidence of the experimentally observed and the theoretically calculated satellite band shape can be used as an ultimate check on the assessment of the quality of potential-energy curves involved in the formation of satellite bands. Received: 1 October 1997 / Revised: 14 January 1998 / Accepted: 24 February 1998     

Improved molecular constants for the and states of NaH

Improved molecular constants for the and states of the NaH molecule are presented. NaH molecules are produced by reactive scattering of H and Na₂ in a crossed beam experiment. High vibrational levels (6 9) of the NaH molecules are predominantly populated. Their excitation spectrum in the range has been measured using a new variant of Doppler spectroscopy. The transition frequencies involving the vibrational levels 2 8 in the and 6 9 in the state have been determined with an accuracy of better than . Using also previously published data a new set of molecular constants for the and state is derived. In particular, the vibrational dependence of the rotational constants B, D and H as well as some of v”-v' band origins for and is determined. The transition frequencies measured here or published previously are reproduced by these new coefficients with an accuracy of 0.1 cm^-1 [rms value] with a maximum deviation of 0.4 cm^-1. New RKR potential energy curves have been calculated up to the turning points of the levels v” = 9 in the state and v' = 25 in the state. Received 21 August 1999     

Accurate calculation of the scattering length for the cooling of hydrogen atoms by lithium atoms

An improved ab initio calculation has been performed for the potential for the LiH a ³Σ⁺ state, using two very large basis sets. The Basis Set Superposition Error (BSSE) correction has been determined for both basis sets and the non-Born-Oppenheimer correction estimated to be negligible. The best potential is approximately 10% deeper than the previous estimate. Vibrational energies and scattering lengths have been calculated for ^6,7LiH(D) with both potentials, with and without the BSSE correction, and also with an estimated potential expected to bracket the true potential. The ⁷LiH scattering length is estimated to be (45 ± 4)a₀ and hence the low-energy cross-section in the best a ³Σ⁺ potential is about half that calculated previously. Enhanced cooling by ⁷Li of trapped H atoms remains feasible. Received 30 April 2001     

High resolution laser spectroscopy of NaAr: Improved interaction potential for the ground state

The absorption spectrum of NaAr has been investigated with high resolution using a supersonic beam of molecules and a tunable dye laser. About 3 300 absorption lines due to the transition A ² Π ← X and B ² Σ ← X have been observed. In addition, we observed the spectral distribution of the fluorescence for a particular absorption line. From all experimental data the X ² Σ ⁺ interaction potential has been deduced in a fully quantum-mechanical method of approach. The potential is given in terms of an analytical Hartree-Fock-Dispersion function. For the equilibrium parameters of the X state we get R _e = 5.01(1) ? and D _e = 41.6(2) cm ^-1 . Received 28 August 2002 / Received in final form 15 October 2002 Published online 17 December 2002 RID="a" ID="a"Now at Knick Elektronische Messger?te, Beuckestr. 22, 14163 Berlin, Germany. RID="b" ID="b"e-mail: dz@kalium.physik.tu-berlin.de     

Rare-gas-induced broadening and shift of two-photon transitions to intermediate Rydberg states of atomic thallium*

Results of broadening and shift measurements of Doppler-free two-photon lines for transitions from the ground state to the Rydberg states with intermediate principle quantum numbers of atomic thallium perturbed by rare gases are reported. The rates show a distinct behaviour in this range of principle quantum numbers and significant dependence on the total angular momentum of the upper nP state. The experimental results are compared with calculations using a Van der Waals potential and a superposition of polarization and Fermi potentials. Additionally, broadening and shift rates of the transition Tl 6P _3/2 -9P _3/2 have been measured for quadrupolar as well as for mainly scalar excitation. The rates for both kinds of excitation coincide within the limits of error reflecting the small perturbation of the 6P _3/2 state compared to that of the upper 9P _3/2 state. Received: 6 August 1997 / Revised in final form: 29 November 1997 / Accepted: 11 December 1997     

Cesium satellite band at 875.2 nm stemming from the Cs 2 0 g + (6 p 2 P 1/2 +6 s 2 S 1/2 ) state

We measured a very distinct satellite band at 875.2 nm between two resonance lines of cesium. Spectral simulation using Spies and Meyer [#!ref1!#] ab initio potential curves and an appropriate transition dipole moment function was compared with experimental profile. Implications of the investigated satellite band at 875.2 nm in the field of ultracold cesium atom collisions are discussed with a special emphasize to new possibilities of the photoassociation of two ground state atoms leading to the formation of ultracold intermediate long-range molecules. Received 07 March 2001 and Received in final form 14 May 2001     

Formation of cold Cs ground state molecules through photoassociation in the pure long-range state

We report on the formation of translationally cold Cs₂ ground state molecules through photoassociation in the 1_u attractive molecular state below the 6 s _1/2 +6 p _3/2 dissociation limit. The cold molecules are obtained after spontaneous decay of photoassociated molecules in a MOT and in a dark SPOT. We also used polarized atoms, in the f =3, m f =+3Zeeman ground state. Purely asymptotic and adiabatic calculations including hyperfine interaction and rotation are in excellent agreement with observed structures. As expected, the 1_u state is actually a pure long-range state, consisting of paired atoms, uniquely linked by the first terms of the multipole expansion of the electrostatic interaction. A temperature of 20 K has been measured for the molecular cloud. Received 19 July 1999     

wave superconductivity: Analysis of the electronic Raman data of and other cuprates

After briefly recalling the d + s model valid for some anisotropic high T c superconductors, we present a theory of electronic Raman spectra in that model and then compare it with new experimental data obtained for an overdoped Y123 single crystal. The d + s model appears to describe satisfactorily the experimental results, indicating a possible doping dependence of the mixing ratio. We note that the Raman spectrum of the overdoped Bi2212 could also be accounted for by the d + s superconductivity model. The case of Hg1212 (or Hg1223) is reexamined. It appears that the spontaneous breakdown of d-wave symmetry may be rather universal in high T c cuprates. Received: 3 March 1998 / Accepted: 30 April 1998     

Quantum and semiclassical dynamics of differential optical collisions

We apply quantum and semiclassical theories to differential optical collisions Na(3²S_1/2) + Kr + Na(3²P_1/2,3/2) + Kr. Our results provide a basis to analyze recent experiments in which for the first time optical collisions were investigated with angular resolution under crossed-beam conditions. A characteristic feature of the differential cross sections is the pronounced oscillatory structure due to interferences of different Condon paths. These Stueckelberg oscillations form an extremely sensitive probe of the collisional dynamics and of the molecular interactions. We demonstrate perspectives to determine geometric properties of the collision complex by excitation with polarized light. By final state analysis nonadiabatic (spin-orbit, rotational) interactions can be studied with complete control of the path. In summary it is shown that the method of differential detection of optical collisions opens a variety of new accesses to atomic and molecular subcollisions. Received: 30 July 1997 / Received in final form: 5 November 1997 / Accepted: 8 January 1998     

Long range interactions of the Mg+ and Ca+ ions

The polarizabilities of the low lying states of the Mg⁺ and Ca⁺ ions are evaluated by diagonalizing the semi-empirical Hamiltonians in a large dimension single electron basis. The quadrupole moment of the metastable 3d state Ca⁺ is also calculated and is within 1% of a recent experimental value while being 5% smaller than some large ab-initio calculations. In addition, the long range dispersion coefficients for these ions interacting with a number of atoms are given. Oscillator strengths are also given and generally agree with the most sophisticated ab-initio calculations. The polarizabilities and dispersion coefficients can be used to estimate the frequency shifts of the Ca⁺ 4s ↦ 3d clock transition due to background electric fields and also collisions with a buffer gas.     

Experimental and theoretical studies of interactions between Si<Subscript>7</Subscript> clusters

The possibility of using magic Si₇ clusters to form a cluster material was studied experimentally and theoretically. In experiments Si₇ clusters were deposited on carbon surfaces, and the electronic structure and chemical properties of the deposited clusters were measured using X-ray photoelectron spectroscopy (XPS). A non bulk-like electronic structure of Si₇ was found in the Si 2p core level spectra. Si₇ is suggested to form a more stable structure than the non-magic Si₈ cluster and Si atoms upon deposition on carbon surfaces. Theoretically it was possible to study the interaction between the clusters without the effect of a surface. Density functional theory (DFT) calculations of potential curves of two free Si₇ clusters approaching each other in various orientations hint at the formation of cluster materials rather than the fusion of clusters forming bulk-like structures.     

Observation of the first vibrations of the newly born Cs-CH CN complex

The femtosecond photodissociation of CsI in the CsI-CH₃CN complex has been studied. Recurrences are observed in the detection of the Cs⁺-CH₃CN ion complex. They are assigned to the first vibrations of the Cs-NCCH₃ bond formed after the CsI dissociation. This result is in good agreement with calculations on the similar NaI-CH₃CN system which predict a linear structure for the ground state complex. Received 27 October 1999     

A rational method for probing macromolecules dissociation: the antibody-hapten system

The unbinding process of a protein-ligand complex of major biological interest was investigated by means of a computational approach at atomistic classical mechanical level. An energy minimisation-based technique was used to determine the dissociation paths of the system by probing only a relevant set of generalized coordinates. The complex problem was reduced to a low-dimensional scanning along a selected distance between the protein and the ligand. Orientational coordinates of the escaping fragment (the ligand) were also assessed in order to further characterise the unbinding. Solvent effects were accounted for by means of the Poisson–Boltzmann continuum model. The corresponding dissociation time was derived from the calculated barrier height, in compliance with the experimentally reported Arrhenius-like behaviour. The computed results are in good agreement with the available experimental data.     

Resonance interaction between one excited and one ground state atom

The nature of the resonance interaction between two isotropic atoms in an excited configuration is reinvestigated. The currently accepted oscillatory form for the long-range retarded resonance interaction is shown to be a subtle artefact that arises due to too drastic approximations. Formulation of the resonance interaction energy problem in terms of the interacting system leads to a form that it is ∝ r ^-4 in the retarded limit. We also demonstrate that the resonance interaction energy at any finite temperature goes over to purely classical long-range asymptote. This manifestation of the correspondence principle is due to thermal excitation of the electromagnetic field. We finally discuss why the textbook result for the F?rster energy transfer between two atoms is incorrect for the same reasons. Received 31 January 2002 / Received in final form 25 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: mtb110@rsphysse.anu.edu.au     

Parametrization of the hybrid potential for pairs of neutral atoms

The hybrid form is a combination of the Rydberg potential and the London inverse-sixth-power energy. It is accurate at all relevant distance scales and simple enough for use in all-atom simulations of biomolecules. One may compute the parameters of the hybrid potential for the ground state of a pair of neutral atoms from their internuclear separation, the depth and curvature of their potential at its minimum, and from their van der Waals coefficient of dispersion C₆.     

Microscopic membrane elasticity and interactions among membrane inclusions: interplay between the shape, dilation, tilt and tilt-difference modes

A phenomenological Landau elasticity for the shape, dilation, and lipid-tilt of bilayer membranes is developed. The shape mode couples with the sum of the monolayers' tilt, while the dilation mode couples with the difference of the monolayers' tilts. Interactions among membrane inclusions within regular arrays are discussed. Inclusions modifying the membrane thickness and/or inducing a tilt-difference due to their convex or concave shape yield a dilation-induced attraction and a tilt-difference-induced repulsion. The resulting interaction can stabilize 2D crystal phases, with the possible coexistence of different lattice spacings when the dilation-tilt-difference coupling is large. Inclusions favoring crystals are those with either a long-convex or a short-concave hydrophobic core. Inclusions inducing a local membrane curvature due to their conical shape repel one another. At short inclusions separations, a tilt comparable with the inclusion's cone angle develops: it relaxes the membrane curvature and reduces the repulsion. At large separations the tilt vanishes, whatever the value of the shape-tilt coupling. Received 23 October 1998 and Received in final form 12 January 1999     

Blue satellite bands of KRb molecule: Intermediate long-range states

Three distinct satellite bands at 730-736 nm and a single shoulder at 755.5 nm that we assigned to KRb heteronuclear molecule are found in absorption measurements of hot K + Rb vapor. The interpretation of these bands is discussed in terms of recent ab initio calculations of the relevant potential curves. Semiclassical spectral simulations were performed with ab initio potentials and approximate transition dipole moment functions showing a good agreement with observations. The probabilities of cold molecule photoassociative formation into the external well of the double minimum (5)0⁺ state and decay to the ground state are discussed, and relative yields of molecular formation were estimated by using quantum mechanical calculations. Received 15 October 2001     

Neutral molybdenum atom and dimer formations in laser-induced plasma: emission study of 355-nm pulse laser photolysis of Mo(CO)6 in the gas phase

6 in the gas phase at room temperature. The transient behavior of emissive atoms and dimers were measured by using a time-resolved UV-vis emission spectroscopy. Most atomic emissions were found to consist of two distinct transient components, an “early” component with a similar time profile to the photolysis pulse, and a “late” component with a peak at around 300 ns after the photolysis. The fact that the addition of an electron scavenger decreased the late emission sensibly suggests that the late emission was caused by Mo^* produced in a neutralization process of ionic species. A plausible mechanism involving electron–ion recombination was proposed for the late emission and examined by the numerical simulation of the transient behaviors as a function of some experimental parameters such as total pressure, initial ion concentration, and electron scavenger concentration. Received: 9 April 1997/Revised version: 12 June 1997     

Development of a ReaxFF description for gold

Atomistic simulations of the chemistry of thiol-gold-systems have been restricted by the lack of interatomic interaction models for the involved elements. The ReaxFF framework already has potentials for hydrocarbons, making it an attractive basis for extending to the complete AuSCH-system. Here, an interatomic potential for gold, based on the ReaxFF framework, is presented and compared to existing gold potentials available in the literature. Electronic supplementary material  Supplementary Online Material