Collisional excitation of C2H and C2D by molecular hydrogen

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Abstract
The determination of physical conditions in interstellar clouds requires reliable estimation of radiative and collisional data for molecules detected in space. In this work, rate coefficients for (de-)excitation of C2H and C2D induced by collisions with both ortho- and para-H2 are presented. Calculations have been carried out using a recently published four dimensional C2H–H2 potential energy surface. Fine structure resolved cross sections were computed with the time-independent close-coupling approach. We report cross sections for transitions between the first 41 levels of C2H and corresponding rate coefficients up to 500 K. We also computed cross sections for transitions between the first 31 levels of C2D and corresponding rate coefficients up to 200 K. Then, hyperfine structure resolved cross sections and rate coefficients were computed using the recoupling technique. The hyperfine structure resolved rate coefficients for C2H–H2 and C2D–H2 are calculated for the first 38 hyperfine C2H energy levels and first 55 hyperfine C2D energy levels both for temperatures up to 100 K. These collisional data were used in a simple radiative transfer modeling.
Funding Information
  • European Research Council (811363)

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