arXiv subjects

S. Kassi

Publications and source records attributed to S. Kassi.

3 recordsLinked to original sources

arXiv2024

Room temperature detection of the (H2)2 dimer

The hydrogen dimer, (H2)2, is among the most weakly bound van der Waals complexes and a prototype species for first principles ab initio studies. The detection of the (H2)2 infrared absorption spectrum was reported more than thirty years ago at a temperature of 20 K. Due to the sharp decrease of the (H2)2 abundance with temperature, a detection at room temperature was generally considered as hardly achievable. Here we report the first room temperature detection of partly resolved rotational structures of (H2)2 by cavity ring down spectroscopy at sub-atmospheric pressures, in the region of the first overtone band of H2 near 1.2 micron. The quantitative analysis of the absorption features observed around ten allowed or forbidden transition frequencies of the monomer provides insight on the structure of this elusive species and a benchmark for future theoretical studies.

physics.chem-ph↗

arXiv2014

High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm-1: Part III-Analysis and theoretical modeling of the 12C17O2, 16O12C17O, 17O12C18O, 16O13C17O and 17O13C18O spectra

More than 19,700 transitions belonging to 11 isotopologues of carbon dioxide have been assigned in the room temperature absorption spectrum of highly 18O enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990 cm-1 (1.71-1.43 \mum). This third and last report is devoted to the analysis of the bands of five 17O containing isotopologues present at very low concentration in the studied spectra: 16O12C17O, 17O12C18O, 16O13C17O, 17O13C18O and 12C17O2 (627, 728, 637, 738 and 727 in short hand notation). On the basis of the predictions of effective Hamiltonian models, a total of 1759, 1786, 335, 273 and 551 transitions belonging to 24, 24, 5, 4 and 7 bands were rovibrationally assigned for 627, 728, 637, 738 and 727, respectively. For comparison, only five bands were previously measured in the region for the 728 species. All the identified bands belong to the \deltaP=8 and 9 series of transitions, where P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 61 bands from a fit of the measured line positions. Two interpolyad resonance perturbations were identified.

physics.atom-ph↗

arXiv2009

Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations

Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen, in which the detection of methane has been reported. Aims: The goal is to constrain essential but so far unknown parameters of Pluto's atmosphere such as the surface pressure, lower atmosphere thermal stucture, and methane mixing ratio. Methods: We use high-resolution spectroscopic observations of gaseous methane, and a novel analysis of occultation light-curves. Results: We show that (i) Pluto's surface pressure is currently in the 6.5-24 microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to explain Pluto's inverted thermal structure and ~100 K upper atmosphere temperature (iii) a troposphere is not required by our data, but if present, it has a depth of at most 17 km, i.e. less than one pressure scale height; in this case methane is supersaturated in most of it. The atmospheric and bulk surface abundance of methane are strikingly similar, a possible consequence of the presence of a CH4-rich top surface layer.

astro-ph.EP↗