V. Boudon

Evidence for a Polar Ethane Cloud on Titan

Spectra from Cassinis Visual and Infrared Mapping Spectrometer reveal the presence of a vast tropospheric cloud on Titan at latitudes 51° to 68° north and all longitudes observed (10° to 190° west). The derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly cool conditions near the moons north pole. Preferential condensation of ethane, perhaps as ice, at Titans poles during the winters may partially explain the lack of liquid ethane oceans on Titans surface at middle and lower latitudes.

Performance of the AILES THz‐Infrared beamline at SOLEIL for High resolution spectroscopy

The new THz beamline (AILES) located at the third generation Synchrotron Radiation source SOLEIL is now operating for applications in a wide variety of research themes. In particular, this source with its adapted optics allows high resolution spectroscopic measurements of molecules in the entire infrared and THz range. This presentation focuses on the performances concerning flux, spectral range and stability for molecular spectroscopy. Thanks to these performances, the coupling of synchrotron radiation from a highly stable third generation source with high resolution FTIR spectrometer and with a long path cell (150 m or more) can be particularly advantageous. This fact is related to the optics of the beamline permitting the entire source to be used without aperture stop (entrance iris), even for measurements at highest‐resolution of ∼0.1 μeV (10−3 cm−1).

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Highly-spherical Top Data System (HTDS) software for spectrum simulation of octahedral XY6 molecules

Abstract The Spherical Top Data System (STDS) program suite developed in Dijon has been extended into two directions. First, the vibrational extrapolation is now possible for any kind of polyad scheme, this one being fully specified in the input parameters of the programs for hamiltonian and transition moment model calculations. This was not the case of the preceding version which was based on the polyad scheme of methane. Secondly, it is now possible to study any band and polyad of XY 6 molecule for which a complete treatment in the O h group is made. Up to now, only some vibrational levels of these molecules ( F 1u levels in particular) could be studied using equivalences with the T d group. Some examples mainly concerning the SF 6 molecule are presented. As before, this suite is composed of a series of FORTRAN programs called by a UNIX script. The whole package is freely accessible through ftp (user anonymous) at jupiter.u-bourgogne.fr.

Orientation of O(3) and SU(2)⊗CI representations in cubic point groups (Oh,Td) for application to molecular spectroscopy

Abstract We propose a detailed method for the symmetrization of the standard O (3) or SU (2)⊗ C I basis | j τ , m 〉 ( τ = g or u ) into the O h or T d point group. This is realized by means of an orientation matrix called G . The oriented basis obtained in this way allows matrix element calculations for rovibronic spectroscopic problems concerning octahedral or tetrahedral molecules. Particular attention has been put on careful phase choices. A numerical calculation of all the G matrix elements for both integer and half-integer j values up to 399/2 has been performed. Such high angular momentum values are necessary for the case of heavy molecules with high rotational excitation. To calculate the G coefficients with high precision at high j values we pre-calculated the necessary Wigner functions using symbolic MAPLE software and made then the numerical calculations with quadruple precision. The complete list of these coefficients can be obtained freely at the URL: http://www.u-bourgogne.fr/LPUB/group.html . As an illustration, we also present briefly an application to two typical spectroscopic calculations: the pure rotational levels of SF 6 in its ground vibrational state and the ν 3 band of ReF 6 (an open-shell molecule with an odd number of electrons and a fourfold degenerate electronic ground state).

Spectroscopy of X2Y4 (D2h) molecules: tensorial formalism adapted to the O(3)⊃D2h chain, Hamiltonian and transition moment operators

Abstract A tensorial formalism adapted to the case of the X2Y4 molecules with D2h symmetry has been developed in the same way as in the previous works on XY4 (Td) and XY6 (Oh) spherical tops and XY5Z (C4v) symmetric tops. Here, we use the O(3)⊃D2h group chain. All the coupling coefficients and formulas for the computation of matrix elements are given for this chain and used in the case of the Hamiltonian and transition moment operators.

High-resolution Fourier transform infrared spectroscopy and analysis of the ν3 fundamental band of P4

Abstract We present the first high-resolution infrared absorption study of the ν 3 fundamental of white phosphorus, P 4 . This spectrum has been analyzed using the STDS (Spherical Top Data System) software. The band center lies at 466.286 cm −1 . With the approximation ( Bζ ) 3 =− B 0 /2, we found that the ground-state bond length is r 0 =219.58 pm. This value is consistent with that of ab initio studies reported previously but significantly different from a value obtained from a Raman study.

Global analysis of the high temperature infrared emission spectrum of 12CH4 in the dyad (ν2/ν4) region

We report new assignments of vibration-rotation line positions of methane ((12)CH4) in the so-called dyad (ν2/ν4) region (1100-1500 cm(-1)), and the resulting update of the vibration-rotation effective model of methane, previously reported by Nikitin et al. [Phys. Chem. Chem. Phys. 15, 10071 (2013)], up to and including the tetradecad. High resolution (0.01 cm(-1)) emission spectra of methane have been recorded up to about 1400 K using the high-enthalpy source developed at Institut de Physique de Rennes associated with the Fourier transform spectrometer of the SOLEIL synchrotron facility (AILES beamline). Analysis of these spectra allowed extending rotational assignments in the well-known cold band (dyad-ground state (GS)) and related hot bands in the pentad-dyad system (3000 cm(-1)) up to Jmax = 30 and 29, respectively. In addition, 8512 new transitions belonging to the octad-pentad (up to J = 28) and tetradecad-octad (up to J = 21) hot band systems were successfully identified. As a result, the MeCaSDa database of methane was significantly improved. The line positions assigned in this work, together with the information available in the literature, were fitted using 1096 effective parameters with a dimensionless standard deviation σ = 2.09. The root mean square deviations dRMS are 3.60 × 10(-3) cm(-1) for dyad-GS cold band, 4.47 ×10(-3) cm(-1) for the pentad-dyad, 5.43 × 10(-3) cm(-1) for the octad-pentad, and 4.70 × 10(-3) cm(-1) for the tetradecad-octad hot bands. The resulting new line list will contribute to improve opacity and radiative transfer models for hot atmospheres, such as those of hot-Jupiter type exoplanets.

Theoretical investigation of the ethylene dimer: Interaction energy and dipole moment

The interaction potential energy and the interaction‐induced dipole moment surfaces of the van der Waals C2H4‐C2H4 complex has been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules. The calculations have been carried out using high‐level ab initio theory with the aug‐cc‐pVTZ basis set and within the framework of the analytical description of long‐range interactions between ethylene molecules. Binding energy for the most stable configuration of the C2H4‐C2H4 complex was calculated at the CCSD(T)/CBS level of theory. The harmonic fundamental vibrational frequencies for this complex were calculated at the MP2 level of theory.

C4v Top Data System (C4v TDS) software for infrared spectrum simulation of XY5Z symmetric molecules

Abstract The Highly spherical Top Data System program suite developed in Dijon has been extended in the aim of studying any rovibrational band or polyad of XY5Z (C4v) symmetric top molecules. We work in the O(3)⊃Oh⊃C4v chain because most of these species result from the substitution of one ligand of the corresponding spherical tops and thus are relatively close to octahedral symmetry. The choice of this group chain has consequences in the way in which it is used to specify the input parameters of the programs for Hamiltonian and transition moment model calculations. One example concerning the ν1/ν8 dyad of the SF 5 35 Cl molecule is presented. As before, this suite consists of a series of FORTRAN programs called as scripts. The whole package is freely accessible through ftp (user anonymous) at jupiter.u-bourgogne.fr or through the World Wide Web at http://www.u-bourgogne.fr/LPUB/c4vTDS.html .