F. Najar

Rotational excitation and de-excitation of C2(X Σ1g+) by para-H2(j=0)

For the van der Waals C(2)(X (1)Sigma(g)(+))-H(2) molecular system, we generated a new ab initio potential energy surface (PES). We mapped this PES at the multireference internally contracted configuration-interaction method including the Davidson correction together with a large diffuse basis set. Then, we incorporated our PES into quantum scattering calculations at the close coupling and infinite order sudden approximation methods to cover collision energies ranging from 0.1 up to 4000 cm(-1). After Boltzmann thermal averaging, rate coefficients for temperatures of up to 1000 K are deduced. Discrepancies between our new rates and those computed previously are noticed. This should induce deviations in astrophysical modeling.

Low-Temperature Rate Constants for Rotational Excitation and De-excitation of C3 (X1Σg+) by Collisions with He (1S)

The low-temperature rotational (de-) excitation of C3 (X1Σg+) by collisions with He (1S) is studied using an ab initio potential energy surface (PES). This PES has been calculated using the single- and double-excitation coupled-cluster approach with noniterative perturbational treatment of triple excitations [CCSD(T)] and the augmented correlation-consistent triple-ζ basis set (aug-cc-pVTZ) with bond functions. This PES is then incorporated in full close-coupling quantum scattering calculations for collision energies between 0.1 and 50 cm−1 in order to deduce the rate constants for rotational levels of C3 up to j = 10, covering the temperature range 5-15 K.