Aims. Rate coefficients for the rotational excitation of the ten lowest levels of ortho-H 2 CO by collisions with H 2 molecules are computed for kinetic temperatures in the range 5−100 K. Methods. Cross sections are obtained from extensive, fully converged, quantum-mechanical scattering calculations using a highly accurate potential energy surface computed at the CCSD(T) level with a basis set extrapolation procedure. Scattering calculations are carried out for H 2 molecules in both para and ortho rotational levels.Results. The present rates are shown to differ significantly from those available in the literature. Moreover, the strength of propensity rules is found to depend on the para/ortho form of H 2 . Radiative transfer modeling also shows that the new rates have a significant impact on H 2 CO emission line fluxes and that they should be adopted in any detailed radiative transfer model of ortho-H 2 CO in cold environments (T < ∼ 30 K).

Context. The ortho-to-para ratio (OPR) of molecular hydrogen is a fundamental parameter in understanding the physics and chemistry of molecular clouds. In dark and cold regions, however, H 2 is not directly observable and the OPR of H 2 in these sources has so far remained elusive. Aims. We show that the 6 cm absorption line of ortho-formaldehyde (H 2 CO) can be employed to constrain both the density and the OPR of H 2 in dark clouds. Methods. Green Bank Telescope (GBT) observations of ortho-H 2 CO toward the molecular cloud Barnard 68 (B68) are reported. Non-LTE radiative transfer calculations combined with the well-constrained structure of B68 are then employed to derive the physical conditions in the absorption region. Results. We provide the first firm confirmation of the Townes & Cheung mechanism: propensity rules for the collisions of H 2 CO with H 2 molecules are responsible for the sub-2.7 K cooling of the 6 cm doublet. Non-LTE calculations show that in the absorption region of B68, the kinetic temperature is ∼10 K, the ortho-H 2 CO column density amounts to ∼2.2 × 10 13 cm −2 , the H 2 density is in the range 1.4−2.4 × 10 4 cm −3 , and the OPR of H 2 is close to zero. Our observations thus provide fresh evidence that H 2 is mostly in its para form in the cold gas, as expected from theoretical considerations. Our results also suggest that formaldehyde absorption originates in the edge of B68, at visual extinctions A V < ∼ 0.5 mag.

S-Genius is a new universal scatterometry platform, which gathers all the LTM-CNRS know-how regarding the rigorous electromagnetic computation and several inverse problem solver solutions. This software platform is built to be a userfriendly, light, swift, accurate, user-oriented scatterometry tool, compatible with any ellipsometric measurements to fit and any types of pattern. It aims to combine a set of inverse problem solver capabilities -via adapted LevenbergMarquard optimization, Kriging, Neural Network solutions -that greatly improve the reliability and the velocity of the solution determination. Furthermore, as the model solution is mainly vulnerable to materials optical properties, S-Genius may be coupled with an innovative material refractive indices determination. This paper will a little bit more focuses on the modified Levenberg-Marquardt optimization, one of the indirect method solver built up in parallel with the total SGenius software coding by yours truly. This modified Levenberg-Marquardt optimization corresponds to a Newton algorithm with an adapted damping parameter regarding the definition domains of the optimized parameters. Currently, S-Genius is technically ready for scientific collaboration, python-powered, multi-platform (windows/linux/macOS), multi-core, ready for 2D-(infinite features along the direction perpendicular to the incident plane), conical, and 3D-features computation, compatible with all kinds of input data from any possible ellipsometers (angle or wavelength resolved) or reflectometers, and widely used in our laboratory for resist trimming studies, etching features characterization (such as complex stack) or nano-imprint lithography measurements for instance. The work about kriging solver, neural network solver and material refractive indices determination is done (or about to) by other LTM members and about to be integrated on S-Genius platform.

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Abstract. We set up a framework for calculating in a precise and controlled way the collisional properties of several molecules of astrophysical meaning. The quantities that are relevant for astrophysics are rotational and vibrational quenching/excitation rates by means of collisions of H2 with water and some organic molecules (HC3 N, H2 CO). We calculate those rates by means of successively determining a intermolecular potential energy surface and calculating inelastic cross sections and rates classically and/or quantum mechanically. These calculations are part of the European Union FP6 Molecular Universe program.Keywords. Astrochemistry, molecular data Computational schemeIn order to understand the intensities of the various lines in molecular rotational spectra of astrophysical origin, we need to know rates of collisional excitation and deexcitation. Molecular hydrogen, H 2 , is by far the more frequent collision partner. Hence, in collaboration with several partners from the European Union 'Molecular Universe' FP6 program, we undertook in Grenoble a large computational program in order to determine some astrophysically relevant inelastic rates, including CO -H 2 rotational excitations, HC 3 N -H 2 and H 2 CO -H 2 rotational excitation and H 2 O -H 2 rotational and rovibrational excitations (see, e. g., Wiesenfeld et al. 2006). Calculating those rates is a twofold endeavor:(a) Calculating the potential energy surface (PES) of the molecule M -molecular hydrogen collision. Since this PES is a non reactive PES, the interaction energy is very small compared with the internal energy of the two collision partners.(b) Using this carefully calibrated PES to perform dynamical calculations in order to compute inelastic cross sections σ kk (E) or inelastic rates k kk (T ), where k, k denote collectively the quantum numbers of the molecule under study, before and after collision. Some Recent Results WaterThe PES for the H 2 O -H 2 interaction was calculated in a very careful way (see Faure et al. 2005 andValiron et al. 2008). The rigid body 5-dimensional interaction potential was determined first, in a very precise calculation, for equilibrium geometries of both the water and hydrogen molecules. Afterwards, a full 9-dimensional (including the vibrational coordinates of H 2 and H 2 O) was computed. It allowed us to determine firstly the collisional matrix elements and rates for vibrational quenching (Faure et al. 2005). Also, averaging the 9-dimensional PES over the ground state vibrational wavefunctions 141 https://www.cambridge.org/core/terms. https://doi