Non-Adiabatic Photonic Processes in Molecular Plasma

When light propagates through a gas of molecules, such as air, it can remove electrons from the molecules, the processes known as photoionization. This process and the one reverse to it, recombination, play an extremely important role in modern technology, in atmospheric sciences, in astrophysics, and many other fields of research. This is the reason why there is a growing need for theoretical methods able to interpret and predict behavior of molecular gases under ionizing radiation.

Although there has been significant progress in a theoretical description of atomic photoionization, the situation with theory in molecular gases is far from being satisfactory. A reliable theoretical description of ionization in molecular gases is complicated due to the complex quantum-mechanical structure of molecules. The main science question of the present project is whether theory can describe photoionization of diatomic molecules, such as those present in air, especially in situations where experimental data do not exist.

The major goal of the project is to develop theoretical methods able to model photoionization of linear molecules (and negatively charged molecular ions). An important broader impact of the proposed research is the development of a web-based platform and a related methodology to teach Quantum Mechanics in studio mode-like classes. The platform allows students and their instructors to perform numerical experiments for all main concepts of Quantum Mechanics.

The photoionization spectrum of molecular nitrogen, N2, will be computed for photon energies above the ionization threshold from the ground vibronic state. Transition dipole moment functions between the N2 ground electronic state and three lowest electronic states of N2+ will be computed and made available to the community. Vibrational and rotation motion of N2 and N2+ will be accounted for as well as non-adiabatic coupling between electronic states of the N2+ ion.

For this purpose, the multichannel quantum defect theory (MQDT) and rovibronic frame transformation will be employed. Using the developed theoretical model of photoionization in N2, cavity-free lasing of N2+, observed in several experimental groups, will be studied. The second objective of the project is to study time-delay and thresholds laws in photodetachment.

The PI will model and study photodetachment spectra of molecular anions, taking into account non-adiabatic effects, interaction of the photoelectron with rotational and vibrational motion of the molecule. The study will include the dependence of main features in the spectra (such as resonances, threshold behavior...) on the dipole moment of the molecule, the rotational and vibrational structure of the molecule, and the presence of one or several dipolar electronic states.

The study will be performed using a FEM (Finite-element method) code able to treat collisions of electrons with linear molecules, solving the Schrodinger equation for electronic and rovibrational motion of the target at the same time. The time-delay in the photodetachment process will be considered and a scheme to observe the time-delay in photodetachment experiments will be developed.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.