engleski

Sulfur molecules in space by X-rays: a computational study

X-ray astronomy lacks high resolution spectra of interstellar dust analogues and molecules, severely hampering interstellar medium (ISM) studies based on upcoming X-ray missions. Various theoretical approaches may be used to address this problem, but they must first be shown to reproduce reliable spectra compared to experiment. In this work, we calculate the sulfur K edge X-ray absorption spectra of H2S, SO2 and OCS, whose spectra are already known from X-ray experiments, and predict the X-ray spectrum of CS, which as far as we are aware has not been measured, thereby hampering its detection by X-ray telescopes. We chose these four molecules as the astrochemistry of sulfur is an unsolved problem, and as the four molecules are already known to exist in space. We consider three types of methods for modeling the X-ray spectra: more accurate calculations with the algebraic-diagrammatic construction (ADC) and the CC2, CCSD and CC3 coupled cluster (CC) approaches, as well as more affordable ones with transition potential density functional theory (TP-DFT). A comparison of our computational results to previously reported experimental spectra shows that the core-valence separation (CVS) approaches CVS-ADC(2)-x and CVS-CC3 generally yield a good qualitative level of agreement with experiment, suggesting they can be used for interpreting measured spectra, while the TP-DFT method is not reliable for these molecules. However, quantitative agreement with experiment is still outside the reach of the computational methods studied in this work.

X-ray spectra ; density functional theory ; algebraic-diagrammatic construction ; coupled cluster methods, astrochemsitry, molecules in space

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