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Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-up Pi resonance
2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 062704Article in journal (Refereed) Published
Abstract [en]

Wepresent an experimental observation of the electronic Doppler effect inresonant Auger spectra upon core excitation slightly above the carbonK edge of the CO molecule. Thus the electronic Dopplereffect has been identified in above-threshold excitation, and in atransition of symmetry. Ab initio calculations of the potentialenergy curves of the relevant states of CO and thewave packet technique have been employed to provide a theoreticalbackground to the experimental studies. The weak feature around 299.4  eVin the photoabsorption spectrum, whose decay has been investigated bythe present experiment, is assigned to double (core-valence) excitations toC 1s shake-up states |1s1−1*2 with a strong dissociative character,and the Doppler splitting of the atomic peak has beenreproduced by the simulation.

Place, publisher, year, edition, pages
APS , 2007. Vol. 76, no 062704
Keyword [en]
ray raman-scattering, photochemistry beamline bl27su, excited-states, shell, photoemission, radiation, dynamics, autoionization, dissociation, spectroscopy
National Category
Theoretical Chemistry
Identifiers
ISI: 000251985900062Scopus ID: 2-s2.0-37249052816OAI: oai:DiVA.org:kth-9733DiVA, id: diva2:127306
Note

Uppdaterad från manuskript till artikel: 20100910 QC 20100910

Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Nuclear Dynamics in X-ray Absorption and Raman Scattering
Open this publication in new window or tab >>Nuclear Dynamics in X-ray Absorption and Raman Scattering
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents theoretical studies of several x-ray spectroscopies - x-ray absorption, x-ray photoelectron emission, radiative and non-radiative resonant Raman scattering spectroscopy. The main focus point is investigating the influence of nuclear dynamics on these spectra for a variety of small molecules - naphthalene, biphenyl, ethylene, the water dimer, HCl, CO. The theoretical tools used consist of the basic equations of the relevant x-ray spectroscopy. Wave packet methods are also used. The molecular parameters needed for our simulations are obtained through suitable quantum chemical calculations, based on either wave function or density functional methods. Our simulations are compared to experimental data, where available.

Simulations of x-ray absorption and x-ray photoionization spectra for naphthalene and biphenyl show that the spectral shapes are heavily influenced by the joint effect of two factors -- chemical shifts and excitations of vibrational progression. Comparison between the two molecules and also comparison to a reference case -- benzene, provides useful insight into the molecular behavior under core excitation.

In a further step, we consider the O1s x-ray photoelectron spectrum of the water dimer. A substantial broadening of the two bands originating from the donor and the acceptor oxygen is found. It is caused by excitations of soft intermolecular vibrational modes, associated with the hydrogen bond.

Another strong influence of the nuclear dynamics is clearly seen in the resonant x-ray Raman scattering of HCl. Vibrational collapse is observed experimentally and confirmed theoretically for distinctive situations. This effect allows to eliminate completely the vibrational broadening, and hence, considerably increase the spectral resolution.

We considered also the vibrational dynamics in resonant soft x-ray Raman scattering from ethylene. The importance of vibronic coupling and symmetry effects is discussed and emphasized. We obtained excellent agreement with the experimental data.

We predict an interference effect in the resonant Auger scattering from fixed-in-space molecules. By exciting a molecule to a dissociative state and measuring the angular distribution of the Auger electrons in coincidence with the molecular ion, one can observe this effect. The interference pattern can be used after Fourier transformation for extracting structural data about the studied system.

We have found that two-center interference leads to an enhancement of the recoil effect.

Finally, it is shown that core excitation to doubly-excited dissociative Pi state is accompanied by Doppler splitting of the atomic peak in resonant Auger scattering from carbon monoxide.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. p. viii, 57
Series
Theses in philosophy from the Royal Institute of Technology, ISSN 1650-8831
Keyword
x-ray scattering, theory, simulations, recoil, Doppler effect, nuclear dynamics, Auger, XPS
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3902 (URN)91-7178-276-1 (ISBN)
Public defence
2006-04-21, FA 32, AlbaNova, Roslagstullsbacken 21, 09:00
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-09-10Bibliographically approved
2. 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 $O1s\rightarrow\sigma^{*}$ 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. p. x, 63
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)
Note
QC 20100917Available from: 2008-12-10 Created: 2008-12-03 Last updated: 2010-09-17Bibliographically approved

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