Quasi-classical rate coefficient calculations for the rotational deexcitation of H2O by H2 - AstrophysicsReport as inadecuate




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Abstract: The interpretation of water line emission from existing observations andfuture HIFI-Herschel data requires a detailed knowledge of collisional ratecoefficients. Among all relevant collisional mechanisms, the rotationaldeexcitation of H2O by H2 molecules is the process of most interest ininterstellar space. To determine rate coefficients for rotational de-excitationamong the lowest 45 para and 45 ortho rotational levels of H2O colliding withboth para and ortho-H2 in the temperature range 20-2000 K. Rate coefficientsare calculated on a recent high-accuracy H2O-H2 potential energy surface usingquasi-classical trajectory calculations. Trajectories are sampled by acanonical Monte-Carlo procedure. H2 molecules are assumed to be rotationallythermalized at the kinetic temperature. By comparison with quantum calculationsavailable for low lying levels, classical rates are found to be accurate withina factor of 1-3 for the dominant transitions, that is those with rates largerthan a few 10^{-12}cm^{3}s^{-1}. Large velocity gradient modelling shows thatthe new rates have a significant impact on emission line fluxes and that theyshould be adopted in any detailed population model of water in warm and hotenvironments.



Author: A. Faure, N. Crimier, C. Ceccarelli, P. Valiron, L. Wiesenfeld, M.-L. Dubernet

Source: https://arxiv.org/







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