Line Coupling Effects in the Isotropic Raman Spectra of N2: A Quantum Calculation at Room Temperature

We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures

PRESSURE BROADENING AND SHIFTING COEFFICIENTS AS TESTS OF H2(D2)-He POTENTIAL ENERGY SURFACES

International audienceWe have calculated the helium-pressure broadening and shifting coefficients of the isotropic Raman Q(1) lines of the fundamental of H 2 and D 2. The quantum dynamical close coupling calculations were performed on five 3-dimensional PESs, namely: the pot3d potential of Bakr et al, 1 the so-called BMP PES, 2 the modified Muchnik and Russek PES, 3 the modified BMP PES, 1 and the Schaefer and Köhler PES. 4 The last one being the oldest one and obtained at the lowest-level of quantum chemical accuracy but has the advantage of covering interactions over a larger intramolecular interval. Moreover, the theoretical values it leads to 5,6,7 are in quite good agreement with experimental pressure broadening and shifting coeffients. 7,8,9,10 By decomposing the kinetic energy dependent pressure broadening cross-sections in an inelastic part and a dephasing one and by also looking at the isotropic contribution of the pressure shifting cross-sections allow us to bring to the fore the main differences that exist between the five PESs we have considered. The modBMP PES has been readily rejected because it is only a slight modification of the original BMP PES. The BMP and modMR PESs lead to thermally averaged values far from the experimental ones. The quantum chemical " state of the art " PES of Bakr et al provides shifting parameters in better agreement than the SK PES with experimental shifts but, the broadening parameters seem to be slightly more accurate with the SK PES. This last point should be confirmed by an accu-

Line Interference Effects Using a Refined Robert-Bonamy Formalism: the Test Case of the Isotropic Raman Spectra of Autoperturbed N2

A symmetrized version of the recently developed refined Robert-Bonamy formalism [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013)] is proposed. This model takes into account line coupling effects and hence allows the calculation of the off-diagonal elements of the relaxation matrix, without neglecting the rotational structure of the perturbing molecule. The formalism is applied to the isotropic Raman spectra of autoperturbed N2 for which a benchmark quantum relaxation matrix has recently been proposed. The consequences of the classical path approximation are carefully analyzed. Methods correcting for effects of inelasticity are considered. While in the right direction, these corrections appear to be too crude to provide off diagonal elements which would yield, via the sum rule, diagonal elements in good agreement with the quantum results. In order to overcome this difficulty, a re-normalization procedure is applied, which ensures that the off-diagonal elements do lead to the exact quantum diagonal elements. The agreement between the (re-normalized) semi-classical and quantum relaxation matrices is excellent, at least for the Raman spectra of N2, opening the way to the analysis of more complex molecular systems

Présentation : Peter Pan n’aura jamais-jamais cent ans

Peter Pan a cent ans, encore.Le personnage imaginé par James Matthew Barrie ne saurait grandir… Comment pourrait-il vieillir et fêter ainsi cent années d’une vie intense faite de rêves, de jeux, et de bien des réécritures ? En revanche, on peut à nouveau célébrer le centenaire du livre écrit par Barrie. Si les personnages de Lewis Carroll se plaisaient à fêter leur non-anniversaire, celui de l’auteur écossais nous offre deux anniversaires à sept ans d’intervalles. C’est le paradoxe de Jamais-..

Muñoz Corcuera, Alfonso et Elisa T. Di Biase. Barrie, Hook, and Peter Pan. Studies in Contemporary Myth; Estudios sobre un mito contemporáneo.

Pour lutter contre le vieillissement et les effets du temps qui passe, on aura beau nous vendre des sérums au venin de serpent, des crèmes à la larme de crocodile, des baumes à base d’écailles de sirènes, on sait bien que rien n’y fera et que le phantasme de jeunesse éternelle restera à jamais réservé à Peter Pan, cet enfant qui ne voulait pas grandir, cet enfant qui se refuse obstinément à grandir et qui veut, pour toujours s’amuser. Voilà peut-être qui explique la pérennité d’un personnage ..

Robust output feedback sampling control based on second order sliding mode

International audienceThis paper proposes a new second order sliding mode output feedback controller. This latter is developped in the case of finite sampling frequency and is using only output information in order to ensure desired trajectory tracking with high accuracy in a finite time in spite of uncertainties and perturbations. This new strategy is evaluated in simulations on an academic example

Line mixing effects in isotropic Raman spectra of pure N2: A classical trajectory study

International audienceLine mixing effects in the Q branch of pure N2 isotropic Raman scattering are studied at room temperature using a classical trajectory method. It is the first study using an extended modified version of Gordon's classical theory of impact broadening and shift of rovibrational lines. The whole relaxation matrix is calculated using an exact 3D classical trajectory method for binary collisions of rigid N2 molecules employing the most up-to-date intermolecular potential energy surface (PES). A simple symmetrizing procedure is employed to improve off-diagonal cross-sections to make them obeying exactly the principle of detailed balance. The adequacy of the results is confirmed by the sum rule. The comparison is made with available experimental data as well as with benchmark fully quantum close coupling [F. Thibault, C. Boulet, and Q. Ma, J. Chem. Phys. 140, 044303 (2014)] and refined semi-classical Robert-Bonamy [C. Boulet, Q. Ma, and F. Thibault, J. Chem. Phys. 140, 084310 (2014)] results. All calculations (classical, quantum and semi-classical) were made using the same PES. The agreement between classical and quantum relaxation matrices is excellent, opening the way to the analysis of more complex molecular systems

Efficient diode-pumped Yb3+:Y2SiO5 and Yb3+:Lu2SiO5 high-power femtosecond laser operation

International audienceWe report the mode-locked operation of two new Yb-doped oxyorthosilicates, Y2SiO5 (YSO) and Lu2SiO5 (LSO), that are longitudinally diode pumped. Yb:YSO supplied pulses as short as 122 fs with 410mW of output power at 1041 nm. More than 2.6W of average output power, for pulse durations of 198 fs at 1044 nm and 260 fs at 1059 nm for Yb:YSO and Yb:LSO, respectively, were provided. These are, to our best knowledge, the highest values ever obtained and the most efficient mode-locked laser in such a classic fibercoupled diode-pumping configuratio

MOLECULAR LINE-SHAPE MODELING FROM FIRST PRINCIPLES

International audienceWe present an ab initio approach to spectral line-shape modeling and the comparison of the results with experimental data

Comparison of quantum, semi-classical and classical methods in the calculation of nitrogen self-broadened linewidths

International audienceWe perform dynamical calculations on two robust N2-N2 potential energy surfaces in order to intercompare pressure broadening coefficients derived from close coupling and coupled states quantum dynamical methods, the semi-classical model of Robert and Bonamy and a full classical method. The coupled states and full classical results compare well with the experimental results or with close coupling values when available. This study confirms that the classical method is a good alternative at room and high temperatures to quantum dynamical methods. The results obtained using the semi-classical method however deviate from the other sets of data at all temperatures considered here (77-2400 K)