Ultrafast absorption of intense x rays by nitrogen molecules.

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry
• X-ray Science

Background:

• Nitrogen molecules (N2) exhibit complex behavior under intense ultrashort X-ray irradiation.
• Understanding these interactions is crucial for interpreting experimental data from advanced light sources like the Linac Coherent Light Source (LCLS).

Purpose of the Study:

• To develop a theoretical framework describing the response of N2 molecules to intense, ultrashort X-ray free-electron laser pulses.
• To elucidate the mechanisms of X-ray-induced ionization and fragmentation in N2.

Main Methods:

• Formulated rate equations for X-ray absorption, incorporating cross sections and decay widths of ionized nitrogen atoms.
• Employed one-electron theory for cross sections and ab initio Dirac-Hartree-Slater (DHS) calculations for decay widths and energies.
• Developed phenomenological models: single atom, symmetric-sharing, and fragmentation-matrix models.

Main Results:

• Calculated ion yields and average charge states, comparing them with LCLS experimental data.
• Investigated the role of single and double core-hole formation and decay.
• Explained the behavior of metastable N2(2+) states and subsequent molecular fragmentation.

Conclusions:

• The theoretical model successfully describes the intricate processes of X-ray interaction with N2 molecules.
• The study provides a detailed understanding of ionization, fragmentation, and the influence of core-hole dynamics.