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 Ultrafast absorption of intense x rays by nitrogen molecules


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We devise a theoretical description for the response of nitrogen molecules N2 to ultrashort and intense x rays from the free electron laser FEL Linac Coherent Light Source LCLS. We set out from a rate-equation description for the x-ray absorption by a nitrogen atom. The equations are formulated using all one-x-ray-photon absorption cross sections and the Auger and radiative decay widths of multiply-ionized nitrogen atoms. Cross sections are obtained with a one-electron theory and decay widths are determined from ab initio computations using the Dirac-Hartree-Slater DHS method. We also calculate all binding and transition energies of nitrogen atoms in all charge states with the DHS method as the difference of two self-consistent field calculations Delta SCF method. To describe the interaction with N2, a detailed investigation of intense x-ray-induced ionization and molecular fragmentation are carried out. As a figure of merit, we calculate ion yields and the average charge state measured in recent experiments at the LCLS. We use a series of phenomenological models of increasing sophistication to unravel the mechanisms of the interaction of x rays with N2: a single atom, a symmetric-sharing model, and a fragmentation-matrix model are developed. The role of the formation and decay of single and double core holes, the metastable states of N 2^2+, and molecular fragmentation are explained.



Autor: Christian Buth; Ji-Cai Liu; Mau Hsiung Chen; James P. Cryan; Li Fang; James M. Glownia; Matthias Hoener; Ryan N. Coffee; Nora Berrah

Fuente: https://archive.org/







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