Ab initio potential energy surfaces describing the interaction of CH(X2Π) with H2

Theoretical Investigation of Rotationally Inelastic Collisions of OH(X2Π) with Hydrogen Atoms

State-to-state cross sections and rate coefficients for transitions between rotational/fine- structure levels of OH(X2Π) induced by collisions with atomic hydrogen are reported in this work. The scattering calculations take into account the full open-shell character of the OH + H system and include the four potential energy surfaces (1A′, 1A′′, 3A′, 3A′′) that correlate with the OH(X2Π) + H(2S) asymptote. Three of these surfaces are repulsive, while the deep H2O well is present on one surface (1A′). The OH + H potential energy curves calculated by Alexander et al. [J. Chem. Phys. 121, 5221 (2004)] are employed in this work. Time independent quantum scattering calculations were performed using the quantum statistical method of Manolopoulos and co-workers [Chem. Phys. Lett. 343, 356 (2001)] because of the presence of the deep H2O well. The computed cross sections include contributions from direct scattering, as well formation and decay of a transient collision complex since the transient HO-H complex is expected to decay nonreactively. Rate coefficients for OH-H inelastic collisions are of interest for astrophysical applications.

Interaction of C2H with molecular hydrogen: Ab initio potential energy surface and scattering calculations

The potential energy surface (PES) describing the interaction of the ethynyl (C₂H) radical in its ground X̃²Σ⁺ electronic state with molecular hydrogen has been computed through restricted coupled cluster calculations including single, double, and (perturbative) triple excitations [RCCSD(T)], with the assumption of fixed molecular geometries. The computed points were fit to an analytical form suitable for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate constants. A representative set of energy dependent state-to-state cross sections is presented and discussed. The PES and cross sections for collisions of H₂(j = 0) are compared with a previous study [F. Najar et al., Chem. Phys. Lett. 614, 251 (2014)] of collisions of C₂H with H₂ treated as a spherical collision partner. Good agreement is found between the two sets of calculations when the H₂ molecule in the present calculation is spherically averaged.

Theoretical investigation of rotationally inelastic collisions of CH(X2Π) with hydrogen atoms

We report calculations of state-to-state cross sections for collision-induced rotational transitions of CH(X²Π) with atomic hydrogen. These calculations employed the four adiabatic potential energy surfaces correlating CH(X²Π) + H(²S), computed in this work through the multi-reference configuration interaction method [MRCISD + Q(Davidson)]. Because of the presence of deep wells on three of the potential energy surfaces, the scattering calculations were carried out using the quantum statistical method of Manolopoulos and co-workers [Chem. Phys. Lett. 343, 356 (2001)]. The computed cross sections included contributions from only direct scattering since the CH₂ collision complex is expected to decay predominantly to C + H₂. Rotationally energy transfer rate constants were computed for this system since these are required for astrophysical modeling.

Theoretical investigation of rotationally inelastic collisions of CH(X2Π) with molecular hydrogen

We report calculations of state-to-state cross sections for collision-induced rotational transitions of CH(X²Π) with molecular hydrogen. These calculations employed the diabatic matrix elements of the interaction potential determined by Dagdigian [J. Chem. Phys. 145, 114301 (2016)], which employed the multi-reference configuration-interaction method [MRCISD+Q(Davidson)]. Because of the presence of a deep well on the lower potential energy surface, the scattering calculations were carried out using the quantum statistical method of Manolopoulos and co-workers [Chem. Phys. Lett. 343, 356 (2001)]. The computed cross sections included contributions from direct scattering, as well as from the formation and decay of a collision complex. The magnitude of latter contribution was found to decrease significantly with increasing collision energy. Rotationally energy transfer rate constants were computed for this system since these are required for astrochemical modeling.