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19 results on '"Wernli, Michael"'

1. Rotational Excitation of HC_3N by H_2 and He at low temperatures

Author

Wernli, Michael, Wiesenfeld, Laurent, Faure, Alexandre, and Valiron, Pierre

Subjects
Physics - Chemical Physics, Astrophysics
Abstract

Rates for rotational excitation of HC3N by collisions with He atoms and H2 molecules are computed for kinetic temperatures in the range 5-20K and 5-100K, respectively. These rates are obtained from extensive quantum and quasi-classical calculations using new accurate potential energy surfaces (PES).

Published
2006
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3. R12-calibrated H2O–H2 interaction: Full dimensional and vibrationally averaged potential energy surfaces.

Author

Valiron, Pierre, Wernli, Michael, Faure, Alexandre, Wiesenfeld, Laurent, Rist, Claire, Kedzˇuch, Stanislav, and Noga, Jozef

Subjects
*POTENTIAL energy surfaces, *QUANTUM chemistry, *MOLECULAR association, *COMPOSITION of water, *VAN der Waals forces, *COLLISIONAL excitation
Abstract

The potential energy surface of H2O–H2 is of great importance for quantum chemistry as a test case for H2O-molecule interactions. It is also required for a detailed understanding of important astrophysical processes, namely, the collisional excitation of water, including the pumping of water masers and the formation of molecular hydrogen on icy interstellar dust grains. We have calculated the interaction for H2O–H2 by performing both rigid-rotor (five-dimensional) and non-rigid-rotor (nine-dimensional) calculations using the coupled-cluster theory at the level of singles and doubles with perturbative corrections for triple excitations [CCSD(T)] with moderately large but thoroughly selected basis set. The resulting surface was further calibrated using high precision explicitly correlated CCSD(T)-R12 calculations on a subset of the rigid-rotor intermolecular geometries. The vibrationally averaged potential is presented in some details and is compared with the most recent rigid-rotor calculations. We explain, in particular, as to why vibrationally averaged rigid-rotor geometries are a better choice than equilibrium geometries. Our fit of the vibrationally averaged surface provides for the first time an accuracy of ∼3 cm-1 in the van der Waals minimum region of the interaction. The overall accuracy of the nine-dimensional surface and fit is lower but remains of the order of 3%–4% of the anisotropy in the domain spanned by the vibrational functions. [ABSTRACT FROM AUTHOR]

Published
2008
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4. The role of rotation in the vibrational relaxation of water by hydrogen molecules.

Author

Faure, Alexandre, Wiesenfeld, Laurent, Wernli, Michael, and Valiron, Pierre

Subjects
ROTATIONAL motion, RELAXATION (Nuclear physics), WATER, MOLECULES, HYDROGEN, QUANTUM theory, MOTION
Abstract

Vibrational relaxation cross sections of the H2O(υ2=1) bending mode by H2 molecules are calculated on a recent high-accuracy ab initio potential-energy surface using quasiclassical trajectory calculations. The role of molecular rotation is investigated at a collisional energy of 3500 cm-1 and it is shown that initial rotational excitation significantly enhances the total (rotationally summed) vibrational relaxation cross sections. A strong and complex dependence on the orientation of the water angular momentum is also observed, suggesting the key role played by the asymmetry of water. Despite the intrinsic limitations of classical mechanics, these exploratory results suggest that quantum approximations based on a complete decoupling of rotation and vibration, such as the widely used vibrational close-coupling (rotational) infinite-order-sudden method, would significantly underestimate rovibrationally inelastic cross sections. We also present some rationale for the absence of dynamical chaos in the scattering process. [ABSTRACT FROM AUTHOR]

Published
2005
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5. A full nine-dimensional potential-energy surface for hydrogen molecule-water collisions.

Author

Faure, Alexandre, Valiron, Pierre, Wernli, Michael, Wiesenfeld, Laurent, Rist, Claire, Noga, Josef, and Tennyson, Jonathan

Subjects
HYDROGEN, QUANTUM electronics, SPECTRUM analysis, WAVE functions, WAVE mechanics, ELECTROMAGNETISM
Abstract

The hydrogen and water molecules are ubiquitous in the Universe. Their mutual collisions drive water masers and other line emission in various astronomical environments, notably molecular clouds and star-forming regions. We report here a full nine-dimensional interaction potential for H2O-H2 calibrated using high-accuracy, explicitly correlated wave functions. All degrees of freedom are included using a systematic procedure transferable to other small molecules of astrophysical or atmospherical relevance. As a first application, we present rate constants for the vibrational relaxation of the υ2 bending mode of H2O obtained from quasiclassical trajectory calculations in the temperature range of 500–4000 K. Our high-temperature (T>=1500 K) results are found compatible with the single experimental value at 295 K. Our rates are also significantly larger than those currently used in the astrophysical literature and will lead to a thorough reinterpretation of vibrationally excited water emission spectra from space. [ABSTRACT FROM AUTHOR]

Published
2005
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6. Molecular collisions in the cold universe Revisited potential energy surfaces and rates for CO, HC3N and H2O in collisions with H2 and He

Author

Wernli, Michael, Wernli, Michael, Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Joseph-Fourier - Grenoble I, and Pierre Valiron(pierre.valiron@obs.ujf-grenoble.fr)

Subjects
interstellar medium, quantum collisions, milieu interstellaire, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], rovibration, taux de collisions, surface d'énergie potentielle, classical collisions, physico-chimie, [SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph], physico-chemistry, collisional rate, Astrophysique moléculaire, collisions classiques, molecular astrophysics, potential energy surface, collisions quantiques
Abstract

WITH THE ADVANCES OF INSTRUMENTS DEDICATED TO MOLECULAR ASTRONOMY MADE DURING THE PAST DECADES AND FORTHCOMING (HERSCHEL AND ALMA), MORE AND MORE MOLECULES ARE DISCOVERED, AND OBSERVED SPECTRA BECOME MORE AND MORE PRECISE. FOR A GOOD UNDERSTANDING OF THESE DATA, ONE NEEDS STATE-TO-STATE COLLISIONAL RATES FOR THE OBSERVED MOLECULES.THE PRECISION OF RATES IS ONE OF THE KEY POINTS OF THIS THESIS: AT THE SAME TIME, WE SEEK THE MAXIMUM PRECISION AND CHARACTERIZE THE NEED AND COST OF PRECISION IN THE CALCULATIONS WE MAKE. CO-H2 IS A SYSTEM OF GREAT ASTROPHYSICAL INTEREST, PREVIOUSLY WIDELY STUDIED. WE SHOW ON THIS SYSTEM THE EQUAL IMPORTANCE OF THE MAIN STEPS OF THE CALCULATION IN THE FINAL PRECISION OF THE RATES. ON HC3N-H2, WE ACHIEVE FOR THE FIRST TIME A FIT OF THE POTENTIAL ENERGY SURFACE (PES) ON A SPHERICAL BASIS ALLOWING US TO CARRY OUT, ALSO FOR THE FIRST TIME, QUANTUM SCATTERING CALCULATIONS. STRONG QUANTUM SELECTION RULES ARE OBTAINED (ABSENT AT THE CLASSICAL LEVEL). THEY SHOULD PLAY A ROLE IN THE ASTROPHYSICAL MODELING OF THIS MOLECULE. THESE RESULTS ARE IN PRINCIPLE TRANSPOSABLE TO ANY LARGE LINEAR MOLECULE. FINALLY, WE BUILD FOR H2O-H2 A NINE-DIMENSIONAL PES, INCLUDING ALL VIBRATIONS. THE ORIGINAL AND AND PRECISE FIT OF THIS SURFACE ALLOWS US TO RULE ON THE OPTIMAL CHOICE OF GEOMETRIES FOR RIGID MOLECULES, AS WELL AS TO COMPUTE ROVIBRATIONAL RATES. THE LATTER, BEING ONE ORDER OF MAGNITUDE LARGER THAN THE PREVIOUS DATA, WILL CHANGE THE INTERPRETATION OF OBSERVATIONS, NOTABLY THOSE OF THE FORTHCOMING HERSCHEL SPACE TELESCOPE., AVEC LES PROGRES DES INSTRUMENTS DEDIES A L'ASTRONOMIE MOLECULAIRE REALISES DURANT LES DERNIERES DECENNIES ET A VENIR (HERSCHEL ET ALMA), TOUJOURS PLUS DE MOLECULES SONT OBSERVEES, ET LES SPECTRES OBTENUS SONT DE PLUS EN PLUS PRECIS. POUR INTERPRETER CES DONNEES, IL FAUT NOTAMMENT DES TAUX DE COLLISION D'ETAT A ETAT POUR LES MOLECULES OBSERVEES.LA PRECISION DES TAUX EST UN DES POINTS CENTRAUX DE CETTE THESE. CECI, AUSSI BIEN DANS LA RECHERCHE D'UN MAXIMUM DE PRECISION QUE DANS LA CARACTERISATION DU BESOIN ET DU COUT DE LA PRECISION DANS LES CALCULS QUE NOUS MENONS. SUR CO-H2, SYSTEME DE GRAND INTERET ASTROPHYSIQUE ET DEJA AMPLEMENT ETUDIE, NOUS ILLUSTRONS L'IMPORTANCE EGALE DES PRINCIPALES ETAPES DU CALCUL DANS LA PRECISION FINALE DES TAUX. SUR HC3N-H2, NOUS PARVENONS POUR LA PREMIERE FOIS A FAIRE UN AJUSTEMENT DE LA SURFACE D'ENERGIE POTENTIELLE (SEP) SUR UNE BASE SPHERIQUE, NOUS PERMETTANT UN TRAITEMENT QUANTIQUE DES COLLISIONS, LUI AUSSI INEDIT. DE FORTES REGLES DE SELECTION QUANTIQUES (ABSENTES AU NIVEAU CLASSIQUE) SONT OBSERVEES, QUI DEVRAIENT JOUER UN ROLE DANS LA MODELISATION ASTROPHYSIQUE DE CETTE MOLECULE. CES RESULTATS SONT EN PRINCIPE TRANSPOSABLES A TOUTES LES GROSSES MOLECULES LINEAIRES. FINALEMENT, NOUS DEVELOPPONS POUR H2O-H2 UNE SEP A NEUF DIMENSIONS INCLUANT TOUTES LES VIBRATIONS. L'AJUSTEMENT ORIGINAL ET PRECIS DE CETTE SURFACE NOUS PERMET DE STATUER SUR LE CHOIX OPTIMAL DE GEOMETRIES INTERNES POUR UNE MOLECULE RIGIDE, AINSI QUE DE CALCULER DES TAUX DE RO-VIBRATION. PLUS GRANDS D'UN ORDRE DE GRANDEUR QUE LES PRECEDENTES DONNEES, ILS MODIFIERONT L'INTERPRETATION DES OBSERVATIONS, NOTAMMENT CELLES A VENIR MENEES PAR LE SATELLITE HERSCHEL.

Published
2006

9. Rotational excitation of water by hydrogen molecules: Comparison of results from classical and quantum mechanics.

Author

Faure, Alexandre, Wiesenfeld, Laurent, Wernli, Michael, and Valiron, Pierre

Subjects
NUCLEAR excitation, QUANTUM theory, HYDROGEN, WATER, PHYSICS, MOLECULES
Abstract

Quasiclassical trajectory calculations are carried out for rotational excitation of water by hydrogen molecules. State-to-state rate coefficients are determined at 100 K and are compared to available quantum results. A good agreement between classical and quantum rates is observed for downward transitions, with an average accuracy of classical results better than a factor of 2. It is thus found that the ambiguities described by Faure and Wiesenfeld [J. Chem. Phys. 121, 6771 (2004)] can be solved in the particular case of waterlike asymmetric-top molecules. [ABSTRACT FROM AUTHOR]

Published
2006
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10. Böden

Author

Egli, Markus, Margreth, Michael, Wernli, Michael, University of Zurich, Haeberli, Wilfried, Keller, Felix, Krüsi, Bertil, Egli, Markus, Rothenbühler, Christine, Meilwes, Judith, and Gruber, Stephan

Subjects
10122 Institute of Geography, 910 Geography & travel
Published
2007

13. Collisions moléculaires inélastiques dans l'univers froid Nouvelles surfaces de potentiel et taux de collision pour CO, HC3N et H2O avec H2 et He

Author

Wernli, Michael, Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Joseph-Fourier - Grenoble I, and Pierre Valiron(pierre.valiron@obs.ujf-grenoble.fr)

Subjects
interstellar medium, quantum collisions, milieu interstellaire, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], rovibration, taux de collisions, surface d'énergie potentielle, classical collisions, physico-chimie, physico-chemistry, collisional rate, Astrophysique moléculaire, collisions classiques, molecular astrophysics, potential energy surface, collisions quantiques
Abstract

WITH THE ADVANCES OF INSTRUMENTS DEDICATED TO MOLECULAR ASTRONOMY MADE DURING THE PAST DECADES AND FORTHCOMING (HERSCHEL AND ALMA), MORE AND MORE MOLECULES ARE DISCOVERED, AND OBSERVED SPECTRA BECOME MORE AND MORE PRECISE. FOR A GOOD UNDERSTANDING OF THESE DATA, ONE NEEDS STATE-TO-STATE COLLISIONAL RATES FOR THE OBSERVED MOLECULES.THE PRECISION OF RATES IS ONE OF THE KEY POINTS OF THIS THESIS: AT THE SAME TIME, WE SEEK THE MAXIMUM PRECISION AND CHARACTERIZE THE NEED AND COST OF PRECISION IN THE CALCULATIONS WE MAKE. CO-H2 IS A SYSTEM OF GREAT ASTROPHYSICAL INTEREST, PREVIOUSLY WIDELY STUDIED. WE SHOW ON THIS SYSTEM THE EQUAL IMPORTANCE OF THE MAIN STEPS OF THE CALCULATION IN THE FINAL PRECISION OF THE RATES. ON HC3N-H2, WE ACHIEVE FOR THE FIRST TIME A FIT OF THE POTENTIAL ENERGY SURFACE (PES) ON A SPHERICAL BASIS ALLOWING US TO CARRY OUT, ALSO FOR THE FIRST TIME, QUANTUM SCATTERING CALCULATIONS. STRONG QUANTUM SELECTION RULES ARE OBTAINED (ABSENT AT THE CLASSICAL LEVEL). THEY SHOULD PLAY A ROLE IN THE ASTROPHYSICAL MODELING OF THIS MOLECULE. THESE RESULTS ARE IN PRINCIPLE TRANSPOSABLE TO ANY LARGE LINEAR MOLECULE. FINALLY, WE BUILD FOR H2O-H2 A NINE-DIMENSIONAL PES, INCLUDING ALL VIBRATIONS. THE ORIGINAL AND AND PRECISE FIT OF THIS SURFACE ALLOWS US TO RULE ON THE OPTIMAL CHOICE OF GEOMETRIES FOR RIGID MOLECULES, AS WELL AS TO COMPUTE ROVIBRATIONAL RATES. THE LATTER, BEING ONE ORDER OF MAGNITUDE LARGER THAN THE PREVIOUS DATA, WILL CHANGE THE INTERPRETATION OF OBSERVATIONS, NOTABLY THOSE OF THE FORTHCOMING HERSCHEL SPACE TELESCOPE.; AVEC LES PROGRES DES INSTRUMENTS DEDIES A L'ASTRONOMIE MOLECULAIRE REALISES DURANT LES DERNIERES DECENNIES ET A VENIR (HERSCHEL ET ALMA), TOUJOURS PLUS DE MOLECULES SONT OBSERVEES, ET LES SPECTRES OBTENUS SONT DE PLUS EN PLUS PRECIS. POUR INTERPRETER CES DONNEES, IL FAUT NOTAMMENT DES TAUX DE COLLISION D'ETAT A ETAT POUR LES MOLECULES OBSERVEES.LA PRECISION DES TAUX EST UN DES POINTS CENTRAUX DE CETTE THESE. CECI, AUSSI BIEN DANS LA RECHERCHE D'UN MAXIMUM DE PRECISION QUE DANS LA CARACTERISATION DU BESOIN ET DU COUT DE LA PRECISION DANS LES CALCULS QUE NOUS MENONS. SUR CO-H2, SYSTEME DE GRAND INTERET ASTROPHYSIQUE ET DEJA AMPLEMENT ETUDIE, NOUS ILLUSTRONS L'IMPORTANCE EGALE DES PRINCIPALES ETAPES DU CALCUL DANS LA PRECISION FINALE DES TAUX. SUR HC3N-H2, NOUS PARVENONS POUR LA PREMIERE FOIS A FAIRE UN AJUSTEMENT DE LA SURFACE D'ENERGIE POTENTIELLE (SEP) SUR UNE BASE SPHERIQUE, NOUS PERMETTANT UN TRAITEMENT QUANTIQUE DES COLLISIONS, LUI AUSSI INEDIT. DE FORTES REGLES DE SELECTION QUANTIQUES (ABSENTES AU NIVEAU CLASSIQUE) SONT OBSERVEES, QUI DEVRAIENT JOUER UN ROLE DANS LA MODELISATION ASTROPHYSIQUE DE CETTE MOLECULE. CES RESULTATS SONT EN PRINCIPE TRANSPOSABLES A TOUTES LES GROSSES MOLECULES LINEAIRES. FINALEMENT, NOUS DEVELOPPONS POUR H2O-H2 UNE SEP A NEUF DIMENSIONS INCLUANT TOUTES LES VIBRATIONS. L'AJUSTEMENT ORIGINAL ET PRECIS DE CETTE SURFACE NOUS PERMET DE STATUER SUR LE CHOIX OPTIMAL DE GEOMETRIES INTERNES POUR UNE MOLECULE RIGIDE, AINSI QUE DE CALCULER DES TAUX DE RO-VIBRATION. PLUS GRANDS D'UN ORDRE DE GRANDEUR QUE LES PRECEDENTES DONNEES, ILS MODIFIERONT L'INTERPRETATION DES OBSERVATIONS, NOTAMMENT CELLES A VENIR MENEES PAR LE SATELLITE HERSCHEL.

Published
2006

14. Influence of a new potential energy surface on the rotational (de)excitation of H2O by H2 at low temperature

Author

Dubernet, Marie-Lise, Daniel, Fabien, Grosjean, Alain, Faure, A., Valiron, Pierre, Wernli, Michael, Rist, Claire, Noga, J., Tennyson, J., Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'astrophysique de l'observatoire de Besançon (UMR 6091) (LAOB), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Department of Physics and Astronomy [UCL London], University College of London [London] (UCL), École normale supérieure - Paris (ENS-PSL), and Debray, Bernard

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]
Published
2006

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