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Description
An accurate analysis of the physical-chemical conditions in the regions of the interstellar medium in which C_3_ is observed requires knowing the collisional rate coefficients of this molecule with He, H_2_, electrons, and H. The main goals of this study are to present the first potential energy surface for the C_3_ +H_2_ complex, to study the dynamics of the system, and to report a set of rate coefficients at low temperature for the lower rotational states of C_3_ with para- and ortho-H_2_. Methods. A large grid of ab initio energies was computed at the explicitly correlated coupled-cluster with single-, double-, and perturbative triple-excitation level of theory, together with the augmented correlation-consistent quadruple zeta basis set (CCSD(T)-F12a/aug-cc-pVQZ). This grid of energies was fit to an analytical function. The potential energy surface was employed in close- coupling calculations at low collisional energies. We present a high-level four-dimensional potential energy surface (PES) for studying the collision of C_3_ with H_2_ . The global minimum of the surface is found in the linear HH-CCC configuration. Rotational deexcitation state-to-state cross sections of C_3_ by collision with para- and ortho-H_2_ are computed. Furthermore, a reduced two-dimensional surface is developed by averaging the surface over the orientation of H_2_. The cross sections for the collision with para-H_2_ using this approximation and those from the four-dimensional PES agree excellently. Finally, a set of rotational rate coefficients for the collision of C_3_ with para- and ortho-H_2_ at low temperatures are reported.
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