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X-ray absorption of N2 accompanied by infrared-induced transitions between the ungerade and gerade core levels
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
2008 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 14, 145601- p.Article in journal (Refereed) Published
Abstract [en]

We study a two-colour pump–probe scheme of x-ray absorption accompanied by core-hole hopping in the field of a strong IR laser. The process is exemplified for fixed-in-space and randomly oriented homonuclear diatomic molecules N2 near the 1σu → 1πg x-ray absorption transition. The laser field mixes the core holes of opposite parities and causes Rabi splitting of the core-excited states. The IR field results in spectral broadening and shifts of the x-ray resonances as well as decrease of x-ray photoabsorption. The Stark broadening of the x-ray absorption spectrum depends on the orientation of the molecule and the angle between the polarization vectors of the x-ray and IR fields. The spectral changes caused by the IR field are weaker for randomly oriented molecules in comparison with fixed-in-space molecules.

Place, publisher, year, edition, pages
2008. Vol. 41, no 14, 145601- p.
Keyword [en]
Absorption, Electromagnetic wave absorption, Pulsed laser deposition, Pumping (laser), Space probes, X ray absorption, Homonuclear diatomic molecules, IR lasers, Pump probe scheme, X ray absorption (XAS)
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-9737DOI: 10.1088/0953-4075/41/14/145601ISI: 000257370200021Scopus ID: 2-s2.0-47249087705OAI: oai:DiVA.org:kth-9737DiVA: diva2:127317
Note

QC 20100916

Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2016-04-20Bibliographically approved
In thesis
1. Quantum nuclear dynamics in  x-ray scattering and lasing
Open this publication in new window or tab >>Quantum nuclear dynamics in  x-ray scattering and lasing
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents a theoretical study of the role of nuclear degrees of freedom in the x-ray absorption, x-ray resonant scattering  and some aspects of the interaction of matter with strong laser fields. Most numerical simulations are performed with a time-dependent wave-packet program that have proved its robustness  in previous investigations. The relevant experimental results are also presented for comparison when available.

The first problem considered in the thesis is the possibility of obtaining x-ray absorption spectra with resolution beyond the natural lifetime broadening of the core-excited electronic states. It is shown that the method of measuring x-ray absorptionin the resonant scattering mode suggested earlier for that purpose exhibits severe limitations originating from the lifetime vibrational interference between the intermediate core-excited vibrational levels. However, a broad class of molecules is found for which spectra with super-high resolution can indeed be obtained. These molecules have parallel potential energy surfaces of the core-excited and final states for the x-ray scattering process.

The interpretations of two interesting cases of x-ray absorption and Auger scattering follow. The first one is related to scattering through a doubly excited Π state in the CO molecule. A Doppler split feature near 299.4 eV and strong scattering anisotropy are  observed. Both features are well explained and reproduced by the theory. Next, theelectron-vibrational fine structure of the excitation for O2 is investigated by means of different models. We are able to single out the electronic states and interpotential crossing points responsible for the peculiar absorption profile. Based on these findings we explain and reproduce the x-ray Auger scattering spectra through the same excitation. Here we encounter a rather unusual situation in which the Auger spectra are affected by three types of the interference: Apart from the lifetime vibrational interference, a strong interference between two intermediate electronic states and an interference with the direct-scattering amplitude is also present.

The process of intramolecular vibrational redistribution (IVR) is investigated in the context of formation of amplified spontaneous emissions (ASE) inside laser-pumped gain media. IVR raises to a higher energy region the threshold pump intensity after which blue-shifted ASE is observed.

Finally, we suggest a new scheme of x-ray pump-probe spectroscopy based on the core-hole hopping in N2 induced by an infrared laser field. We investigate the result from the core-hole hoping on the vibrational structure of the x-ray absorption profile. Furthermore, by populating core-excited states with opposite parities, the laser field opens up symmetry forbidden resonant inelastic scattering channels, which can give new insights about the electronic structure of matter.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. x, 63 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2008:28
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9728 (URN)978-91-7415-159-6 (ISBN)
Public defence
2008-12-17, FB42, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100917Available from: 2008-12-10 Created: 2008-12-03 Last updated: 2010-09-17Bibliographically approved

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