Classical and quantum mechanical plane switching in CO2

Classical plane switching takes place in systems with a pronounced 1:2 resonance, where the degree of freedom with lowest frequency is doubly-degenerate. Under appropriate conditions, one observes a periodic and abrupt precession of the plane in which the doubly-degenerate motion takes place. In this article, we show that quantum plane switching exists in CO2 : Based on our analytical solutions of the classical Hamilton's equations of motion, we describe the dependence on vibrational angular momentum and energy of the frequency of switches and the plane switching angle. Using these results, we find optimal initial wave packet conditions for CO2 and show, through quantum mechanical propagation, that such a wave packet indeed displays plane switching at energies around 10000 cm-1 above the ground state on time scales of about 100 fs.Comment: accepted for publication in the Journal of Chemical Physic

Quaternionic Dirac oscillator

International audienceAbstract We construct an elementary quaternionic slow–fast Hamiltonian dynamical system with one formal control parameter and two slow degrees of freedom as half-integer spin in resonance 1:1:2 with two slow oscillators. Invariant under spin reversal and having a codimension-5 crossing of its fast Kramers-degenerate semi-quantum eigenvalues, our system is the dynamical equivalent of the spin-quadrupole model by Avron et al (1989 Commun. Math. Phys. 124 595–627), exhibiting non-Abelian geometric phases. The equivalence is uncovered through the equality of the spectral flow between quantum superbands and Chern numbers c 2 computed by Avron et al

GAS PHASE ROVIBRATIONAL SPECTROSCOPY OF DMSO, PART.I: WHEN A SYNCHROTRON SOURCE REVEALS AN UNUSUAL ROTATIONAL BEHAVIOUR

Author Institution: Laboratoire de Physico-Chimie de l'Atmosphere, 189A Ave. Maurice; Schumann, 59140 Dunkerque, France; Ligne AILES, synchrotron SOLEIL; L'Orme des Merisiers, Saint Aubin, BP 48, 91192 Gif-sur-Yvette, France.Many of us have enjoyed the spectacle of a spinning top influenced by friction: rotating rapidly about a stable stationary axis, the top loses slowly its angular momentum j (and energy), slows down gradually, and then, suddenly, its axis becomes unstable, the top wobbles, and an abrupt change of the top's position follows. In other words, the system undergoes a bifurcation. In the case of the tippe top, rotation about its lower point is stable at low values of angular momentum J and becomes unstable at large J. Something quite similar occurs in a freely rotating dimethylsulfoxyde (DMSO, (CH$_3$)$_2$SO) molecule. For the first time in such large polyatomic molecule a quantum bifurcation induced by a gyroscopic destabilization was observed. , \textbf{109},(094101), 2012.} This unusual phenomenon in rotational dynamics was discovered in the rovibrational states of the bending fundamental $\nu_{23}$ band of DMSO whose high-resolution gas phase absorption spectrum was observed along with that of $\nu_{11}$ by Cuisset et al. , \textbf{492},(30),2010} using the exceptional properties of the AILES beamline in the Far-Infrared domain. , \textbf{1214}, (81), 2010.

GAS PHASE THZ SPECTROSCOPY OF ORGANOSULFIDE AND ORGANOPHOSPHOROUS COMPOUNDS USING A SYNCHROTRON SOURCE

Author Institution: Laboratoire de Physico-Chimie de l'Atmosphere, 189A Ave. Maurice; Schumann, 59140 Dunkerque, France; Ligne AILES, synchrotron SOLEIL; L'Orme des Merisiers, Saint Aubin, BP 48, 91192 Gif-sur-Yvette, France.This study concerns the gas phase rovibrational spectroscopy of organosulfide and organophosphorous which are considered as non toxic model compounds in the analysis of chemical weapon materials, high pathogenic and mutagenic agents, and other environmentally interesting air-borne species. %Since several years, different agencies provided support for research aiming at examining the potential of different optical sensors able to unambiguously identify the chemical agents. In this context, we undertook a study aiming at evaluating the potential use of THz waves for the detection and the identification of organosulfide and organophosphorous compounds. The coupling of the synchrotron radiation with multipass cells and the FTIR spectrometer allowed to obtain very conclusive results in term of sensitivity and resolution and improved the previous results obtained with classical sources., 2008, \textbf{112:}, 12516-12525} For DMSO, using an optical path of 150 m the spectra have been recorded at the ultimate resolution of 0.001 cm$^{-1}$ allowing to fully resolve the rotational structure of the lowest vibrational modes observed in the THz region. In the 290 \-- 420 cm$^{-1}$ region, the rovibrational spectrum of the perpendicular and parallel vibrational bands associated with, respectively, the asymmetric $\nu_{23}$ and symmetric $\nu_{11}$ bending modes of DMSO have been recorded with a resolution of $1.5\times 10^{-3}$ cm$^{-1}$. , 2010, \textbf{492:} 30-34} %The analysis of the $\nu_{23}$ and $\nu_{23}$ yielded accurate rotational constants and centrifugal corrections both in the ground and the excited states. The gas phase vibrational spectra of organophosphorous compounds were measured by FTIR spectroscopy using the vapor pressure of the compounds. Except for TBP, the room temperature vapor pressure was sufficient to detect all active vibrational modes from THz to NIR domain. Contrary to DMSO, the rotational patterns of alkyl phosphates and alkyl phosphonates could not be resolved; only a vibrational analysis may be performed. Nevertheless, the spectral fingerprints observed in the THz region allowed a clear discrimination between the molecules and between the different molecular conformations. , 2010, \textbf{114:} 16936-16947.

FAR INFRARED HIGH RESOLUTION SYNCHROTRON FTIR SPECTROSCOPY OF THE LOW FREQUENCY BENDING MODES OF DMSO

Author Institution: Laboratoire de Physico-Chimie de l'Atmosphere, CNRS UMR-8101; Universite du Littoral Cote d'Opale, 189A Ave. Maurice; Schumann, 59140 Dunkerque, France; Ligne AILES (Advance InfraRed Line Exploited for Spectroscopy), synchrotron SOLEIL; L'Orme des Merisiers, Saint Aubin, BP 48, 91192 Gif-sur-Yvette, France.In addition to its importance for industrial and environmental studies, the monitoring of DiMethylSulfOxyde (DMSO, (CH$_3$)$_2$SO) concentrations is of considerable interest for civil protection. The existing high resolution gas phase spectroscopic data of DMSO only concerned the pure rotational transitions in the ground state.,nderline{\textbf{260},(23),2009}} In the Far-IR domain, the low-frequency rovibrational transitions have never previously resolved.,nderline{\textbf{599},(177),2001}} The high brightness of the AILES beamline of the synchrotron SOLEIL and the instrumental sensitivity provided by the multipass cell allowed to measure for the first time these transitions.,nderline{accepted for publication}} 1581 A-type and C-type transitions in the $\nu_{11}$ band have been assigned and 25 molecular constants of Watson's s-form hamiltonian developped to degree 8 have been fitted within the experimental accuracy. The use of then synchrotron radiation has opened many possibilities for new spectroscopic studies. Together with several other recent studies, our successful measurement and analysis of DMSO convincingly demonstrates the potential of the AILES beamline for high resolution FIR spectroscopy. Thus our present work is just at the beginning of unraveling the rovibrational structure of low frequency bending and torsional vibrational states of DMSO and yielding important comprehensive structural and spectroscopic information on this molecule