Marc Joyeux

Ultra-fast underwater suction traps

Carnivorous aquatic Utricularia species catch small prey animals using millimetre-sized underwater suction traps, which have fascinated scientists since Darwins early work on carnivorous plants. Suction takes place after mechanical triggering and is owing to a release of stored elastic energy in the trap body accompanied by a very fast opening and closing of a trapdoor, which otherwise closes the trap entrance watertight. The exceptional trapping speed—far above human visual perception—impeded profound investigations until now. Using high-speed video imaging and special microscopy techniques, we obtained fully time-resolved recordings of the door movement. We found that this unique trapping mechanism conducts suction in less than a millisecond and therefore ranks among the fastest plant movements known. Fluid acceleration reaches very high values, leaving little chance for prey animals to escape. We discovered that the door deformation is morphologically predetermined, and actually performs a buckling/unbuckling process, including a complete trapdoor curvature inversion. This process, which we predict using dynamical simulations and simple theoretical models, is highly reproducible: the traps are autonomously repetitive as they fire spontaneously after 5–20 h and reset actively to their ready-to-catch condition.

Energy Localization in Molecules, Bifurcation Phenomena, and Their Spectroscopic Signatures: The Global View

Institute of Electronic Structure and Laser, Foundation for Research and TechnologysHellas, and Department of Chemistry, University of Crete, Iraklion 711 10, Crete, Greece, Max-Planck-Institut fur Dynamik und Selbstorganisation, D-37073 Gottingen, Germany, Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, and Laboratoire de Spectrometrie Physique, Universite Joseph FouriersGrenoble I, BP 87, F-38402, St. Martin d’Heres Cedex, France

van der Waals states in ozone and their influence on the threshold spectrum of O3(X1A1). I. Bound states.

Threshold spectra of several isotopomers of ozone are studied using accurate quantum mechanical calculations and an ab initio potential energy surface. Shallow van der Waals minima in the dissociation channels, separated from the deep main wells by an 80 cm−1 high barrier, are shown to accommodate long progressions of assignable states. As a result, dense vibrational spectrum of ozone near dissociation is dominated by van der Waals-type states for all studied isotope compositions.

Intra–inter polyad mixing and breaking of symmetric–antisymmetric selection rule in the vibrational spectra of CS2 molecule

A laser system composed of tunable lasers pumped by a copper vapor laser (Oxford Lasers Cu60) is described in this paper. The high resolution obtained with this system has allowed excitation of selective rotational levels of the 15 V and 10 V vibrational bands of the V 1B2 excited electronic state of the CS2 molecule in its vapor phase (∼100 mTorr). The rotational assignment of the excitation spectra was accomplished by observing the dispersed fluorescence. We show that it is not necessary to use a supersonic jet in order to assign the emission spectra of CS2. The goal of this work is to study the highly excited vibrational states of the ground electronic state of CS2 up to the first dissociation limit. For our purpose, there are two important consequences of the particular geometry of the 15 V excitation, which is just below and close to the bending potential barrier of the V 1B2 state. First, a very good Franck–Condon overlap in the excitation and a large Franck–Condon access to high vibrational states,...

Spectroscopy, dynamics, and chaos of the CS2 molecule: Fourier transform and phase‐space analysis

In this paper we analyze the vibrational spectra of the Σ+g ground state of CS2, the experimental results of which have been described in a forth coming paper. We show that, up to 12 000 cm−1, CS2 can be described by a system of two degrees of freedom strongly coupled by a 1:2 type Fermi resonance. The corresponding vibrational spectra are refitted with the aid of only seven parameters. Analysis of the spectra by the statistical Fourier transform technique reveals stroboscopic effects between the symmetric stretching mode and the bending mode. The distinction between the ‘‘stroboscopic hole’’ due to these effects and the ‘‘correlation hole’’ due to nonintegrable terms in the Hamiltonian is discussed in detail. The study of the topology of the phase space of CS2 in the regular and chaotic cases is carried out in the basis described by a vibrational angular momentum which includes the Fermi resonance. We show the analogy between the localization of the wave packets of the eigenstates and the trajectories. W...

Semiclassical study of the isomerization states of HCP

The vibrational spectrum of HCP (phosphaethyne) is studied and analyzed in terms of a 1:2 resonance effective Hamiltonian. The parameters of the model Hamiltonian are determined by fitting 361 out of the first 370 energy levels obtained from diagonalization of the full Hamiltonian, which is based on a newly calculated potential-energysurface with near spectroscopic accuracy. It is demonstrated that all features characteristic of the approach to the HCP↔CPH isomerization, such as the strong mixing between the bending and CP-stretching motions, the appearance of “isomerization states” (large amplitude bending motion) at intermediate energies, and the diagnostically significant appearance of a zig–zag pattern in the energy spacings between neighboring levels within each polyad, are quantitatively reproduced by the effective Hamiltonian. The semiclassical analysis of the model Hamiltonian for specific combinations of the HC-stretch and polyad quantum numbers explains all of the observed features of the full Hamiltonian in terms of stable and unstable periodic orbits. In particular, the birth of the isomerization states is found to be related to a saddle-node bifurcation of the classical phase space. The connection with the “polyad phase sphere” representation of quantum polyads is also discussed.

Gustavson’s procedure and the dynamics of highly excited vibrational states

The well-known Birkhoff–Gustavson canonical perturbation theory has been used so far to obtain a reasonable approximation of model systems near the bottom of the well. It is argued in the present work that Gustavson’s calculation procedure is also a powerful tool for the study of the dynamics of highly excited vibrational states, as soon as the requirement that the transformed Hamiltonians be in Birkhoff’s normal form is dropped. Mathematically, this amounts to modifying the content of Gustavson’s null space. Physically, the transformed Hamiltonians are of the single or multiresonance type instead of just trivial Dunham expansions, even though no exact resonance condition is fulfilled. This idea is checked against 361 recently calculated levels of HCP up to 22 000 cm−1 above the bottom of the well and involving up to 30 quanta in the bending degree of freedom. Convergence up to 13th order of perturbation theory and an average absolute error as low as 2.2 cm−1 are reported for a two-resonance Hamiltonian, ...

Dynamical model based on finite stacking enthalpies for homogeneous and inhomogeneous DNA thermal denaturation.

We present a nonlinear dynamical model for DNA thermal denaturation, which is based on the finite stacking enthalpies used in thermodynamical nearest-neighbor calculations. Within this model, the finiteness of stacking enthalpies is shown to be responsible for the sharpness of calculated melting curves. Transfer-integral and molecular dynamics calculations are performed to demonstrate that the proposed model leads to a good agreement with known experimental results for both homogeneous and inhomogeneous DNA.

Vibrational analysis of HOCl up to 98% of the dissociation energy with a Fermi resonance Hamiltonian

We have analyzed the vibrational energies and wave functions of HOCl obtained from previous ab initio calculations [J. Chem. Phys. 109, 2662 (1998); 109, 10273 (1998)]. Up to approximately 13 000 cm−1, the normal modes are nearly decoupled, so that the analysis is straightforward with a Dunham model. In contrast, above 13 000 cm−1 the Dunham model is no longer valid for the levels with no quanta in the OH stretch (v1=0). In addition to v1, these levels can only be assigned a so-called polyad quantum number P=2v2+v3, where 2 and 3 denote, respectively, the bending and OCl stretching normal modes. In contrast, the levels with v1⩾2 remain assignable with three vi quantum numbers up to the dissociation (D0=19 290 cm−1). The interaction between the bending and the OCl stretch (ω2≅2ω3) is well described with a simple, fitted Fermi resonance Hamiltonian. The energies and wave functions of this model Hamiltonian are compared with those obtained from ab initio calculations, which in turn enables the assignment of ...

Optical measurements of methyl group tunneling in molecular crystals: Temperature dependence of the nuclear spin conversion rate

The tunneling methyl groups in dimethyl‐s‐tetrazine (DMST) doped single crystals of durene were investigated by high resolution optical spectroscopy using spectral hole burning. The experiments probe the level structure as well as the relaxation dynamics of the tunneling methyl groups in different electronic states of DMST. The tunneling splitting differs by 1.24 GHz in the ground and the first excited singlet states of DMST. In the ground electronic state, relaxation (spin conversion) between the spin 3/2 (A) and 1/2 (E) tunneling levels was measured between 1.5 and 12 K. The spin conversion time is larger than 100 h at 1.5 K and decreases with Arrhenius‐type behavior above 3.5 K. The activation energy of 20 cm−1 also is observed as a phonon sideband in emission, and is, in agreement with theoretical predictions, tentatively assigned to a librational mode of the methyl group.