Rotational relaxation of SiCSi by collision with para-H2(j=0)

The SiCSi molecule has been detected in the interstellar medium (ISM) and is expected to play a key role in astrochemistry. To correctly determine the physicochemical conditions in typical molecular clouds, the use of non-local thermodynamic equilibrium models is essential. These models require the rate coefficients of the molecule analyzed with the most common ISM colliders. However, for SiCSi, these data are not available. The main objective of this work is to determine the first set of rotational rate coefficients for SiCSi collision with para-H-2(j = 0). For this purpose, a recently reported reduced potential energy surface is employed. Quantum dynamics is studied from close-coupling calculations. Furthermore, a set of cross-sections is computed using the coupled-states methods and compared with the close-coupling results. The rate coefficients are compared with the values of an approximation used recently in the literature, showing the need to determine these data from accurate calculations. Finally, the de-excitation rate coefficients are reported for the first 31 rotational states of SiCSi at low temperatures.

Automated summary

The SiCSi molecule has been detected in the interstellar medium and is important in astrochemistry. Non-local thermodynamic equilibrium models are necessary to determine the physicochemical conditions in molecular clouds. However, there is a lack of rate coefficients for SiCSi, the collision partner with para-H-2(j = 0). This study aims to determine the first set of rotational rate coefficients using quantum dynamics calculations and cross-sections. The findings highlight the need for accurate calculations and provide de-excitation rate coefficients for SiCSi at low temperatures.