Inelastic H + H${}_3^{+}$ Collision rates and their impact in the determination of the excitation temperature of H${}_3^{+}$

Abstract

Context. In dffuse interstellar clouds the excitation temperature derived from the lowest levels of H${}_3^{+}$ is systematically lower than that derived from H2. The differences may be attributed to the lack of state-specific formation and destruction rates of H${}_3^{+}$ needed to thermalize the two species. Aims. In this work, we want to check the role of rotational excitation collisions of H${}_3^{+}$ with atomic hydrogen on its excitation temperature. Methods. A time independent close-coupling method is used to calculate the state-to-state rate coefficients, using a very accurate and full dimensional potential energy surface recently developed for H${}_4^{+}$. A symmetric top approach is used to describe a frozen H${}_3^{+}$ as equilateral triangle. Results. Rotational excitation collision rate coefficients of H${}_3^{+}$ with atomic Hydrogen have been derived in a temperature range appropriate to diffuse interstellar conditions up to $(J;K;\pm )=(7;6;+)$ and $(J;K;\pm )=(6;4;+)$ for its ortho and para forms. This allows to have a consistent set of collisional excitation rate coefficients and to improve the previous study where these contributions were speculated. Conclusions. The new state-specific inelastic H${}_3^{+}$ + H rate coeffcients yield differences up to 20% in the excitation temperature, and their impact increases with decreasing molecular fraction. We also confirm the impact of chemical state-to-state destruction reactions in the excitation balance of H${}_3^{+}$ , and that reactive H + H${}_3^{+}$ collisions are also needed to account for possible further ortho to para transitions

9 pages,9 figures

References in corpus (6)

• A parsec-scale Galactic 3D dust map out to 1.25 kpc from the Sun
• A global potential energy surface for H${}_3^{+}$
• High accuracy calculations of the rotation-vibration spectrum of H${}_3^{+}$
• Experimental and theoretical studies of D + H${}_3^{+}$ $\to$ H${}_2$D${}^{+}$ + H
• H${}_3^{+}$ absorption and emission in local U/LIRGs with JWST/NIRSpec: Evidence for high H${}_2$ ionization rates
• Vibrational, non-adiabatic and isotopic effects in the dynamics of the H${}_2$ + H${}_2^{+}$ $\to$ H${}_3^{+}$ + H reaction: application to plasma modeling

Cited by in corpus (1)

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