73 research outputs found
The 2015 edition of the GEISA spectroscopic database
The GEISA database (Gestion et Etude des Informations Spectroscopiques AtmosphĂ©riques: Management and Study of Atmospheric Spectroscopic Information) has been developed and maintained by the ARA/ABC(t) group at LMD since 1974. GEISA is constantly evolving, taking into account the best available spectroscopic data. This paper presents the 2015 release of GEISA (GEISA-2015), which updates the last edition of 2011 and celebrates the 40th anniversary of the database. Significant updates and additions have been implemented in the three following independent databases of GEISA. The âline parameters databaseâ contains 52 molecular species (118 isotopologues) and transitions in the spectral range from 10â6 to 35,877.031 cmâ1, representing 5,067,351 entries, against 3,794,297 in GEISA-2011. Among the previously existing molecules, 20 molecular species have been updated. A new molecule (SO3) has been added. HDO, isotopologue of H2O, is now identified as an independent molecular species. Seven new isotopologues have been added to the GEISA-2015 database. The âcross section sub-databaseâ has been enriched by the addition of 43 new molecular species in its infrared part, 4 molecules (ethane, propane, acetone, acetonitrile) are also updated; they represent 3% of the update. A new section is added, in the near-infrared spectral region, involving 7 molecular species: CH3CN, CH3I, CH3O2, H2CO, HO2, HONO, NH3. The âmicrophysical and optical properties of atmospheric aerosols sub-databaseâ has been updated for the first time since 2003. It contains more than 40 species originating from NCAR and 20 from the ARIA archive of Oxford University. As for the previous versions, this new release of GEISA and associated management software facilities are implemented and freely accessible on the AERIS/ESPRI atmospheric chemistry data center website
Air-broadening coefficients of CH335Cl and CH337Cl rovibrational lines and their temperature dependence by a semi-classical approach
International audienc
Line shape modelling by current semiclassical approaches
International audienc
Collisional broadening of molecular rovibronic lines
To meet burning needs of high-resolution pressure-induced line-shape parameters in the UV/visible regions for hot-temperature industrial and atmospheric applications as well as current and future space missions, phase-shift theory is examined in its historical context, tested and revisited using accurate numerical potentials and advanced trajectory models. First, a general analysis for arbitrary molecular systems is conducted in terms of the dimensionless parameter α determined by the differences of the Lennard-Jones parameters in the final and initial electronic absorber's states. Temperature dependence, use of the power law and influence of MaxwellâBoltzmann averaging over relative velocities are addressed. Then, interaction-potential calculations are attempted for some representative molecular pairs (NO-Ar, NO-N2, OH-Ar and OH-N2) and the isotropic parts are fitted using the 12-6 Lennard-Jones form to get room and high-temperature line-broadening and line-shift coefficients which are compared to available measurements. It is shown that the phase-shift theory in its standard rectilinear-trajectory formulation provides linewidth and shift estimates accurate within 30%â40%. Attempted improvements using numerical potentials and curved trajectories lead to closer matches with measurements for some cases but also worsen the agreement for others. To ensure better theoretical predictions, introduction of correction terms to the usual phase-shift integral is suggested
Line mixing in Raman scattering spectra of CO2 modelled by a non-Markovian Energy-Corrected Sudden approach
International audienc
Exact treatment of classical trajectories governed by an isotropic potential for linewidth computations
Two models for exact classical trajectories in the field of an isotropic potential are investigated for the purpose of semiclassical linebroadening calculations. The first directly uses the exact solution of the classical equation of motion. The second starts from the equation of motion and computes the trajectory by numerical solution of the differential equations. In the framework of both models, all the computations are performed numerically, thus allowing the use of refined ab initio potential energy surfaces. For the example of the linebroadening of pure nitrogen and carbon monoxide, it is shown that, owing to the dominant short-range forces in these self-perturbed molecular systems, the limiting case corresponding to traditional parabolic trajectories can be used without any important loss of precision
Semi-classical H 2 -broadening coefficients of 12 CH 3 D rovibrational lines and their temperature dependence for planetary atmosphere modeling
International audienc
Nitrogen and Oxygen broadening of ozone infrared lines in the 5 micrometer region: theoretical predictions by semiclassical and semiempirical methods
International audiencePressure broadening coefficients of the O3âN2(O2) vibrotational lines at room temperature were computed in the framework of the semiclassical formalism of Robert and Bonamy improved by exact trajectories, and a semiempirical approach based on the Anderson theory. In the first method, a more precise trajectory description enables a good (up to a few percent) reproduction of the experimental data available in the literature, but is characterized by a quite high CPU cost. In the second method, a simplified form of the scattering matrix accounts for the subtle effects of the trajectory curvature and vibrational dependence via effective adjustable parameters and noticeably reduces the CPU time without a loss of precision for further systematic computations. In contrast to the case of the water molecule, these parameters exhibit a quite pronounced dependence on the rotational quantum number J values of the lines used for fitting and should be properly adjusted for transitions from low, middle and high rotational levels
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