Tensor cross sections and collisional depolarization of MgH by He atoms

Rotational Excitation of the CP(Χ2Σ+) Open Shell Molecule Due to Collision with He(1S)

Phosphorus bearing molecules have been discovered in the circumstellar and interstellar media. Modeling their abundance accurately requires computations of rate coefficients induced by collision with He and H₂ (i.e., the most abundant gaseous components). These calculations may be carried out by first determining highly accurate potential energy surface (PES) and cross sections. In this paper, we present the first PES of the CP(X²Σ⁺)-He(¹S) van der Waals collisional complex. The ab initio interaction potential was performed using the explicitly correlated restricted coupled cluster approach with simple, double, and perturbative triple excitation (RCCSD(T)-F12) in connection with the augmented-correlation consistent-polarized valence triple-ζ Gaussian basis set (aug-cc-pVTZ). The potential presents two minima of -18.62 cm^-1 and -18.72 cm^-1. From the PES obtained, we have computed state-to-state excitation cross sections of CP due to collision with He for energies up to 500 cm^-1. Rotational transitions involving the fine-structure levels of the CP molecule were treated with a recoupling technique based on the scattering matrix calculated with the exact quantum mechanical close coupling method. Discussions on the propensity rules between the fine-structure levels were made and we found that the Δj = ΔN transitions are favored with respect to the Δj ≠ ΔN ones. The data presented in this paper may have a great impact on the accurate determination of the CP abundance in space.

Mg2H2: new insight on the Mg-Mg bonding and spectroscopic study

The six dimensional potential energy surface of the electronic ground state X̃(1)Σ(g)(+) of Mg(2)H(2) has been generated by the coupled-cluster approach with single, double and perturbative triple excitations [CCSD(T)] combined with the aug-cc-pCVTZ basis set for Mg atoms and the aug-cc-pVTZ basis set for the H atoms. The analytical representation of this surface was used in variational calculations of the rovibrational energies of Mg(2)H(2), Mg(2)D(2), and HMg(2)D for J = 0 and 1. For Mg(2)H(2), the rotational constant B(0) is computed to be 0.1438 cm(-1), and the fundamental anharmonic wavenumbers are calculated to be ν(1) = 1527.3 cm(-1) (Σ(g)(+)), ν(2) = 275.3 cm(-1) (Σ(g)(+)), ν(3) = 1503.6 cm(-1) (Σ(u)(+)), ν(4) = 312.9 cm(-1) (Π(g)), and ν(5) = 256.5 cm(-1) (Π(u)). In addition, the electronic ground states of Mg(2)H, MgH(2), Mg(2), and MgH have been investigated in order to compute the bonding energies of Mg(2)H(2) and to explain the strength of the Mg-Mg bond in this tetra-atomic molecule. The nature of the low-lying excited states of Mg(2)H(2) is also studied.