Mixed Quantum/Classical Theory for Collisional Quenching of PAHs in the Interstellar Media
ACS Earth and Space Chemistry
Original Item ID
A computationally affordable methodology is developed to predict cross sections and rate coefficients for collisional quenching and excitation of large molecules in space, such as PAHs. Mixed quantum/classical theory of inelastic scattering (MQCT) is applied, in which quantum state-to-state transitions between the internal states of the molecule are described using a time-dependent Schrodinger equation, while the scattering of collision partners is described classically using mean-field trajectories. To boost the numerical performance even further, a decoupling scheme for the equations of motion and a Monte Carlo sampling of the initial conditions are implemented. The method is applied to compute cross sections for rotational excitation and quenching of a benzene molecule (C6H6) by collisions with He atoms in a broad range of energies, using a very large basis set of rotational eigenstates up to j = 60, and close to one million nonzero matrix elements for state-to-state transitions. The properties of collision cross sections for C6H6 + He are reported and discussed. The accuracy of the approximations is rigorously tested and is found to be suitable for astrophysical/astrochemical simulations. The method and code developed here can be employed to generate a database of collisional quenching rate coefficients for PAHs and other large molecules, such as iCOMs, or for molecule–molecule collisions in cometary comas.
Babikov, Dmitri, "Mixed Quantum/Classical Theory for Collisional Quenching of PAHs in the Interstellar Media" (2022). Chemistry Faculty Research and Publications. 1063.
Accepted version. ACS Earth and Space Chemistry, Vol. 6, No. 3 (October 2022): 521-529. DOI© 2022 ACS Publications. Used with permission.