| 1. |
- Banerjee, Ambar, 1985-, et al.
(författare)
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Simulating fluorine K -edge resonant inelastic x-ray scattering of sulfur hexafluoride and the effect of dissociative dynamics
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 108:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on a computational study of resonant inelastic x-ray scattering (RIXS), at different fluorine K-edge resonances of the SF6 molecule, and corresponding nonresonant x-ray emission. Previously measured polarization dependence in RIXS is reproduced and traced back to the local σ and π symmetry of the molecular orbitals and corresponding states involved in the RIXS process. Also electron-hole coupling energies are calculated and related to experimentally observed spectator shifts. The role of dissociative S-F bond dynamics is explored to model detuning of RIXS spectra at the |F1s-16a1g1) resonance, which shows challenges to accurately reproduce the required steepness for core-excited potential energy surface. We show that the RIXS spectra can only be properly described by considering breaking of the global inversion symmetry of the electronic wave function and core-hole localization, induced by vibronic coupling. Due to the core-hole localization we have symmetry forbidden transitions, which lead to additional resonances and changing width of the RIXS profile.
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| 2. |
- Blinov, Svyatoslav N., et al.
(författare)
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Mapping molecular potentials using pump-probe spectroscopy of vibrational wave packets' revival
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 108:1
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the nuclear dynamics in nitrogen monoxide after valence ionization by a pump pulse and subsequent probing with a time-delayed x-ray pulse. We calculate the development of the resulting vibrational wave packet, taking into account three different ionization mechanisms: one-photon, multiphoton, and tunneling ionization. Using a two-time propagation method, we solve the nonstationary nuclear Schrödinger equation to obtain time-resolved x-ray absorption spectra (TRXAS), considering the finite duration of the probe pulse. Our simulations show that the TRXAS profile accurately reflects the vibrational wave packets' trajectory in the cationic ground state. Additionally, we find that the TRXAS evolution is highly sensitive to small changes in the probed potential energy curve, making it a useful tool for reconstructing molecular potentials and determining anharmonicity and equilibrium bond length. This method can be applied to other polyatomic molecules and pump mechanisms.
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| 3. |
- Ekholm, V., et al.
(författare)
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Core-hole localization and ultra-fast dissociation in SF6
- 2020
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:18
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra excited at the fluorine K resonances of SF(6)have been recorded. While a small but significant propensity for electronically parity-allowed transitions is found, the observation of parity-forbidden electronic transitions is attributed to vibronic coupling that breaks the global inversion symmetry of the electronic wavefunction and localizes the core hole. The dependence of the scattering cross section on the polarization of the incident radiation and the scattering angle is interpreted in terms of local pi/sigma symmetry around the S-F bond. This symmetry selectivity prevails during the dissociation that occurs during the scattering process.
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| 4. |
- Gel'mukhanov, Faris, et al.
(författare)
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Dynamics of resonant x-ray and Auger scattering
- 2021
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Ingår i: Reviews of Modern Physics. - : American Physical Society (APS). - 0034-6861 .- 1539-0756. ; 93:3
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Forskningsöversikt (refereegranskat)abstract
- Anoverview of both experimental and theoretical results in the field of resonant scattering of tunable soft and hard x-ray radiation is presented, with a main focus on the closely related processes of resonant inelastic x-ray scattering (RIXS) and resonant Auger scattering (RAS). The review starts with an overview of fundamental dynamical aspects of RIXS illustrated for different systems. A detailed analysis of case studies with increasing complexity, considering both gas-phase and condensed matter (liquids and solids) applications, is given. In the review, the most important achievements in investigations of coupled electron-nuclear dynamics and structural aspects in studies of liquids and solids over the last two decades are outlined. To give a perspective on the insights from RIXS and RAS, the x-ray results are discussed against the background of complementary experimental techniques like vibrational infrared absorption and Raman spectroscopy, as well as small-angle x-ray and neutron scattering. Finally, recent achievements in time-resolved studies based on x-ray free-electron lasers are described.
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| 5. |
- Gel'mukhanov, Faris, et al.
(författare)
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Nonlocal resonant inelastic x-ray scattering
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 108:5
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Tidskriftsartikel (refereegranskat)abstract
- In the description of resonant inelastic x-ray scattering (RIXS) from inversion-symmetric molecules the small core-level splitting is typically neglected. However, the spacing Δ between gerade and ungerade core levels in homonuclear diatomic molecules can be comparable with the lifetime broadening of the intermediate core-excited state Γ. We show that when Δ∼Γ the scattering becomes nonlocal in the sense that x-ray absorption at one atomic site is followed by emission at the other one. This is manifested in an unusual dependence of the RIXS cross section on the sum of the momenta of incoming and outgoing x-ray photons k+k′, contrary to the normal k-k′ dependence in the conventional local RIXS theory. The nonlocality of the scattering influences strongly the scattering angle and excitation energy dependence of the intensity ratio between parity forbidden and allowed RIXS channels. Numerical simulations for N2 show that this effect can readily be measured at present-day x-ray radiation facilities.
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| 6. |
- Jadoun, Deependra, 1998-
(författare)
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Non-linear Spectroscopy of Conical Intersections with XUV and X-ray Photons
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Conical intersections (CIs) appear in a molecule due to the breakdown of the Born-Oppenheimer approximation when the energy difference between two or more electronic states decreases. CIs are known to play a crucial role in processes such as photosynthesis and vision in the human eye, and therefore it is important to probe the existence of such entities in molecules. Observing phenomena such as population transfer, electronic coherence generation, and vanishing electronic states separation can help probe a CI in a molecule. However, the accurate observation of the occurrence of CIs is challenging primarily due to the femtosecond time scale of such non-adiabatic processes in molecules.This thesis explores non-linear spectroscopic methods that can help detect the presence of a CI in a molecule. Multiple techniques such as photoelectron spectroscopy, transient absorption, spontaneous emission, and Raman spectroscopy with classical and entangled photons were theoretically investigated. Special emphasis was placed on observing electronic coherence near a CI, as it provides compelling evidence for the presence of a CI in a molecule. The significance of attosecond pulse trains was investigated in time-resolved photoelectron spectroscopy to improve the visibility of electronic coherence and population transfer features. A two-dimensional extension of the Raman technique TRUECARS was developed to generate Raman signals that lack vibrational coherence, thus helping visualize electronic coherences in a molecule. Entangled photons were also employed in Raman spectroscopy to probe CIs with simultaneously high temporal and spectral resolutions, which is unachievable by classical pulses.
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| 7. |
- Liu, Ji Cai, et al.
(författare)
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Complementarity in which-path resonant Auger scattering
- 2024
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 109:2
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Tidskriftsartikel (refereegranskat)abstract
- Different types of Young's double-slit experiments contain a significant amount of both particle and wave information running from full-particle to full-wave knowledge depending on the experimental conditions. We study the Young's double-slit interference in resonant Auger scattering from homonuclear diatomic molecules where opposite Doppler shifts for the dissociating atomic slits provide path information. Different quantitative formulation of Bohr's complementarity principle - path information vs interference - is applied to two types of resonant Auger scattering experiments, with fixed-in-space and randomly oriented molecules. Special attention is paid to the orientational dephasing in conventional Auger experiments with randomly oriented molecules. Our quantitative formulation of the complementarity is compared with the formulation made earlier by Greenberger and Yasin [D. M. Greenberger and A. Yasin, Phys. Lett. A 128, 391 (1988)0375-960110.1016/0375-9601(88)90114-4].
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| 8. |
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| 9. |
- Liu, Ji-Cai, et al.
(författare)
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High-resolution x-ray spectra of carbon monoxide reveal ultrafast dynamics induced by long UV pulse
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- In theoretical simulations of a UV + x-ray pump-probe (UVX-PP) setup, we show that frequency detuning of the pump UV pulse acts as a camera shutter by regulating the duration of the UVX-PP process. This two-photon absorption with long overlapping UV and x-ray pulses, allowing for high spectral resolution, thereby provides information about ultrafast dynamics of the nuclear wave packet without the requirement of ultrashort pulses and controlled delay times. In a case study of carbon monoxide, the calculated UVX-PP spectra of the O1s (-1)2 pi (1) and C1s (-1)2 pi (1) core-excited states show different vibrational profiles. The interference of intermediate vibrational states reveals details of nuclear dynamics in the UVX-PP process related to a variable duration time controlled by the UV detuning. Both O1s (-1)2 pi (1) and C1s (-1)2 pi (1) pump-probe channels display a splitting of the spectral profile, which however is associated with different physical mechanisms. At the O1s (-1)2 pi (1) resonance, the observed dispersive and non-dispersive spectral bands intersect and result in destructive interference.
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| 10. |
- Liu, Ji-Cai, et al.
(författare)
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Polarization-sensitive IR-pump-x-ray-probe spectroscopy
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and core-ionization spectra of molecules pumped by two coherent infrared pulses with different polarizations are studied theoretically. We have found a sensitivity of the vibrational profile of x-ray probe spectra to polarizations of the IR and x-ray pulses. This polarization dependence is qualitatively different for x-ray absorption and x-ray photoelectron spectra. Measurements of this polarization dependence allow to select the difference in Franck-Condon distributions from the lowest and pumped vibrational levels of the electronic ground state. The proposed technique is exemplified numerically using x-ray absorption spectra of the pumped CO molecule. We also show that this kind of pump-probe spectroscopy can enable studies of the dynamics of molecular rotation.
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| 11. |
- Liu, Ji-Cai, et al.
(författare)
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Role of the Cohen-Fano interference in recoil-induced rotation
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:11
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Tidskriftsartikel (refereegranskat)abstract
- We study the rotational dynamics induced by the recoil effect in diatomic molecules using time-resolved two-color x-ray pump-probe spectroscopy. A short pump x-ray pulse ionizes a valence electron inducing the molecular rotational wave packet, whereas the second time-delayed x-ray pulse probes the dynamics. An accurate theoretical description is used for analytical discussions and numerical simulations. Our main attention is paid to the following two interference effects that influence the recoil-induced dynamics: (i) Cohen-Fano (CF) two-center interference between partial ionization channels in diatomics and (ii) interference between the recoil-excited rotational levels manifesting as the rotational revival structures in the time-dependent absorption of the probe pulse. The time-dependent x-ray absorption is computed for the heteronuclear CO and homonuclear N-2 molecules as showcases. It is found that the effect of CF interference is comparable with the contribution from independent partial ionization channels, especially for the low photoelectron kinetic energy case. The amplitude of the recoil-induced revival structures for the individual ionization decreases monotonously with a decrease in the photoelectron energy, whereas the amplitude of the CF contribution remains sufficient even at the photoelectron kinetic energy below 1 eV. The profile and intensity of the CF interference depend on the phase difference between the individual ionization channels related to the parity of the molecular orbital emitting the photoelectron. This phenomenon provides a sensitive tool for the symmetry analysis of molecular orbitals.
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| 12. |
- Liu, J. -C, et al.
(författare)
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Time-resolved study of recoil-induced rotation by X-ray pump - X-ray probe spectroscopy
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:11, s. 6627-6638
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Tidskriftsartikel (refereegranskat)abstract
- Modern stationary X-ray spectroscopy is unable to resolve rotational structure. In the present paper, we propose to use time-resolved two color X-ray pump-probe spectroscopy with picosecond resolution for real-time monitoring of the rotational dynamics induced by the recoil effect. The proposed technique consists of two steps. The first short pump X-ray pulse ionizes the valence electron, which transfers angular momentum to the molecule. The second time-delayed short probe X-ray pulse resonantly excites a 1s electron to the created valence hole. Due to the recoil-induced angular momentum the molecule rotates and changes the orientation of transition dipole moment of core-excitation with respect to the transition dipole moment of the valence ionization, which results in a temporal modulation of the probe X-ray absorption as a function of the delay time between the pulses. We developed an accurate theory of the X-ray pump-probe spectroscopy of the recoil-induced rotation and study how the energy of the photoelectron and thermal dephasing affect the structure of the time-dependent X-ray absorption using the CO molecule as a case-study. We also discuss the feasibility of experimental observation of our theoretical findings, opening new perspectives in studies of molecular rotational dynamics.
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| 13. |
- Santos, A. C. F., et al.
(författare)
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Resonant Auger decay induced by the symmetry-forbidden 1a(1g)? 6a(1g) transition of the SF6 molecule
- 2022
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Ingår i: Journal of Vacuum Science & Technology A. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 40:4
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Tidskriftsartikel (refereegranskat)abstract
- Resonant Auger electron spectroscopic study at the symmetry-forbidden 1 a 1 g -> 6 a 1 g excitation below the S K-shell threshold of SF 6 is reported. Partial electron yield and resonant K L L Auger spectra have been measured by using monochromatized undulator synchrotron radiation. By changing the photon energy in small steps, a so-called 2D map is produced. In this map, the dipole-forbidden transition exhibits spectral features (e.g., an S-shaped dispersion relation), which are well known and understood for dipole-allowed transitions. We validate by a theory that for the case of dipole-forbidden transitions, these spectral features can be analyzed in the same way as previously established for the dipole-allowed ones. This approach grants information on the nuclear dynamics in the K-shell core-excited states of SF 6 on the femtosecond (fs) timescale. In particular, for the potential-energy curves of the states S 1 s(-1) 6(a1g) and S 2p(-2)6a(1g), the slopes at the equilibrium distance of the ground state are derived. Symmetry breaking as a result of ultrafast vibronic coupling is revealed by the population of the electronically forbidden excited state. Published under an exclusive license by the AVS.
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| 14. |
- Savchenko, Viktoriia, et al.
(författare)
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Dynamical phase shift in x-ray absorption and ionization spectra by two delayed x-ray laser fields
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- We study theoretically x-ray absorption and ionization spectra of an atom or molecule by two coherent x-ray pulses that show a relative phase shift resulting in a time delay of the pulse envelopes. We demonstrate that the phase modulation of the spectra is shifted with respect to the phase oscillation comb of the x-ray double pulse. The reason for this shift is the dynamics of the process defined by the interplay of the delay time, the pulse width, the detuning, and the lifetime of the core-excited state.
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| 15. |
- Savchenko, Viktoriia, et al.
(författare)
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Hydrogen bond effects in multimode nuclear dynamics of acetic acid observed via resonant x-ray scattering
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:21
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical and experimental study of the gas phase and liquid acetic acid based on resonant inelastic x-ray scattering (RIXS) spectroscopy is presented. We combine and compare different levels of theory for an isolated molecule for a comprehensive analysis, including electronic and vibrational degrees of freedom. The excitation energy scan over the oxygen K-edge absorption reveals nuclear dynamic effects in the core-excited and final electronic states. The theoretical simulations for the monomer and two different forms of the dimer are compared against high-resolution experimental data for pure liquid acetic acid. We show that the theoretical model based on a dimer describes the hydrogen bond formation in the liquid phase well and that this bond formation sufficiently alters the RIXS spectra, allowing us to trace these effects directly from the experiment. Multimode vibrational dynamics is accounted for in our simulations by using a hybrid time-dependent stationary approach for the quantum nuclear wave packet simulations, showing the important role it plays in RIXS.
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| 16. |
- Savchenko, Viktoriia
(författare)
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Multidimensional nuclear dynamics studied by resonant X-ray scattering and pump-probe spectroscopy
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the theoretical studies of the multidimensional nuclear dynamics in molecules with the help of X-ray and pump-probe spectroscopy. Using an accurate yet computationally cheap mixed approach multimode X-ray absorption spectra (XAS) and resonant inelastic X-ray scattering (RIXS) spectra of water, methanol, and acetic acid were calculated and compared with the available experimental spectra in the gas and liquid phases. Based on a theoretical study of RIXS in a water molecule through the dissociative core-excited state ∣O1s−14a11⟩, the dynamic origin of the splitting of the lone pair RIXS resonance ∣1b1−14a11⟩ was proved. This result also explains the dynamic nature of the splitting of this peak in liquid water. The decisive role of multimode nuclear dynamics in explaining the experimental XAS and RIXS spectra of methanol, as well as the splitting of the lone pair peak, was theoretically substantiated. RIXS anisotropy effects were fully considered and discussed. The role of hydrogen bonds on vibrational RIXS in the gas phase and liquid acetic acid was analyzed. In contrast to the gas phase, the quasi-elastic RIXS of oxygen K-edge of liquid acetic acid does not exhibit a long vibrational progression, which is qualitatively different from water and methanol. We explained this behavior by the unusually strong influence of the hydrogen bond, which changes the character of the intermediate core-excited state. The combined theoretical-experimental study allowed us to obtain information on the local structure and quantum nuclear dynamics in the liquid system. Besides the advanced theory of RIXS, we developed theory for several new pump-probe techniques, where infrared (IR), ultraviolet (UV), or X-ray pump is combined with XAS or X-ray photoemission spectra (XPS) as a probe. Using accurate theoretical simulations for CO molecule, we show strong sensitivity of X-ray spectra to the relative polarization between IR-pulses and X rays, which can be effectively used for extraction of the weak IR-induced signal. In the framework of UV-pump X-ray probe (UVX-PP) spectroscopy for long overlapping pulses, we show the qualitative difference of the UVX-PP spectra vibrational structure from that of RIXS, allowing for a complementary study of the potential energy surfaces of the valence- and coreexcited molecular states. In the scheme utilizing two time-delayed X-ray pulses we show theoretically that the phase modulation of the XAS is shifted with respect to the phase oscillation comb of the X-ray double pulse, reflecting the dynamics of the light interaction with a quantum system.
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| 17. |
- Savchenko, Viktoriia, et al.
(författare)
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Photodissociation of water induced by a long UV pulse and probed by high-energy-resolution x-ray-absorption spectroscopy
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 104:3
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Tidskriftsartikel (refereegranskat)abstract
- A UV-pump x-ray-probe (UVX-PP) experiment for probing UV initiated dissociation of the water molecule with long pulses is proposed on the basis of theoretical simulations. With long overlapping UV and x-ray pulses, we can obtain high-spectral-resolution x-ray-absorption or ionization spectra, containing detailed information about dynamics in the intermediate valence-excited state. The dynamics can be influenced with frequency detuning of the pump UV pulse, which acts as a camera shutter by regulating the duration of the UVX-PP process. Thereby, this UVX-PP setup gives access to ultrafast dynamics of the nuclear wave packet without experimentally challenging requirements of ultrashort pulses and controlled delay times. In a case study of the water molecule, we focus on the lowest UVX-PP channel (1b(1) -> 4a(1), 1a(1) -> 1b(1)) where both intermediate valence-excited and final core-excited states are dissociative. The variation of the UVX-PP duration, controlled by the UV detuning, and different dispersion laws of so-called molecular and atomic bands allow one to study the dynamics of fragmentation of the water molecule in the intermediate state. A feature is that the long lifetime of intermediate valence-excited states opens a door for studies of photoinduced dissociation of polyatomic molecules with heavy fragments.
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| 18. |
- Savchenko, Viktoriia, et al.
(författare)
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Vibrational resonant inelastic X-ray scattering in liquid acetic acid : a ruler for molecular chain lengths
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O-H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.
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| 19. |
- Savchenko, Viktoriia, et al.
(författare)
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Wave packet theory for non-resonant x-ray emission and non-resonant Auger electron emission in molecules
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 159:4
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Tidskriftsartikel (refereegranskat)abstract
- We present a time-dependent theory for non-resonant x-ray emission spectrum (XES) and normal Auger spectrum (NAS) calculation, based on a fully quantum description of nuclear dynamics using the vibrational wave packet concept. We compare two formulations of the time-dependent theory, either employing a two-time propagation scheme or using spectral integration over the electron energy continuum. We find that the latter formulation is more efficient for numerical simulations, providing a reasonable accuracy when the integration step is shorter than the lifetime broadening of the core-ionized state. We demonstrate our approach using the example of non-resonant x-ray emission from a water molecule, considering the lowest core-ionized K−1 and first core-ionized shake-up K−1V−1V1 intermediate states. These channels exemplify the developed theory on bound–bound, bound–continuum, continuum–bound, and continuum–continuum transitions. Our results suggest that the time-dependent approach is efficient for simulating XES involving dissociative states, whereas the time-independent approach, based on Franck–Condon factors, is more efficient for bound–bound transitions expressed as discrete frequency dependence in the energy domain. The methods and discussion have general applicability, including both NAS and more complex systems, such as liquid water.
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| 20. |
- Söderström, Johan, et al.
(författare)
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Parity violation in resonant inelastic soft x-ray scattering at entangled core holes
- 2024
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 10:7, s. 3114-
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering (RIXS) is a major method for investigation of electronic structure and dynamics, with applications ranging from basic atomic physics to materials science. In RIXS applied to inversion-symmetric systems, it has generally been accepted that strict parity selectivity applies in the sub-kilo-electron volt region. In contrast, we show that the parity selection rule is violated in the RIXS spectra of the free homonuclear diatomic O2 molecule. By analyzing the spectral dependence on scattering angle, we demonstrate that the violation is due to the phase difference in coherent scattering at the two atomic sites, in analogy with Young's double-slit experiment. The result also implies that the interpretation of x-ray absorption spectra for inversion symmetric molecules in this energy range must be revised.
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| 21. |
- Travnikova, O., et al.
(författare)
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Ultrafast dissociation of ammonia : Auger Doppler effect and redistribution of the internal energy
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:10, s. 5842-5854
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Tidskriftsartikel (refereegranskat)abstract
- We study vibrationally-resolved resonant Auger (RAS) spectra of ammonia recorded in coincidence with the NH2+ fragment, which is produced in the course of dissociation either in the core-excited 1s−14a11 intermediate state or the first spectator 3a−24a11 final state. Correlation of the NH2+ ion flight times with electron kinetic energies allows directly observing the Auger-Doppler dispersion for each vibrational state of the fragment. The median distribution of the kinetic energy release EKER, derived from the coincidence data, shows three distinct branches as a function of Auger electron kinetic energy Ee: Ee + 1.75EKER = const for the molecular band; EKER = const for the fragment band; and Ee + EKER = const for the region preceding the fragment band. The deviation of the molecular band dispersion from Ee + EKER = const is attributed to the redistribution of the available energy to the dissociation energy and excitation of the internal degrees of freedom in the molecular fragment. We found that for each vibrational line the dispersive behavior of EKERvs. Ee is very sensitive to the instrumental uncertainty in the determination of EKER causing the competition between the Raman (EKER + Ee = const) and Auger (Ee = const) dispersions: increase in the broadening of the finite kinetic energy release resolution leads to a change of the dispersion from the Raman to the Auger one.
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