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Feasibility of Valence-to-Core X-ray Emission Spectroscopy for Tracking Transient Species.

March AM, Assefa TA, Bressler C, Doumy G, Galler A, Gawelda W, Kanter EP, Németh Z, Pápai M, Southworth SH, Young L, Vankó G - J Phys Chem C Nanomater Interfaces (2015)

Bottom Line: Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit.In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES for time-resolved experiments.We discuss technical improvements that will make valence-to-core XES a practical pump-probe technique.

View Article: PubMed Central - PubMed

Affiliation: X-ray Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.

ABSTRACT

X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. X-ray absorption spectroscopy (XAS) is considered an established technique for such measurements, and X-ray emission spectroscopy (XES) of the strongest core-to-core emission lines (Kα and Kβ) is now being utilized. Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit. In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES for time-resolved experiments. We discuss technical improvements that will make valence-to-core XES a practical pump-probe technique.

No MeSH data available.


Measured ironvalence-to-1s core XES compared with DFT-simulated spectrum. (top)Measured vtc XES of 0.4 M aqueous [Fe(CN)6]4– and the calculated spectrum for the same ion. (bottom) Spectrumof sodium nitroprusside, in solid form, and calculations for the [Fe(CN)5(NO)]2– ion. Representations of the maincontributing molecular orbitals are shown.
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fig2: Measured ironvalence-to-1s core XES compared with DFT-simulated spectrum. (top)Measured vtc XES of 0.4 M aqueous [Fe(CN)6]4– and the calculated spectrum for the same ion. (bottom) Spectrumof sodium nitroprusside, in solid form, and calculations for the [Fe(CN)5(NO)]2– ion. Representations of the maincontributing molecular orbitals are shown.

Mentions: Roughly 50 eV to higherenergy, on the tail of the core-to-core Kβ1,3 spectrum,is the vtc region which exhibits more sensitivity to the chemicalenvironment of the absorbing metal ion and hence more spectral variationfor different chemical species than core-to-core Kβ. Measuredand calculated vtc spectra of aqueous [FeII(CN)6]4– are shown in the top panel of Figure 2. The intensity is considerably weaker than thatfor the core-to-core Kβ1,3 fluorescence, with a peakcount rate of 130 counts per second as compared to 4200 counts persecond. The features of the Kβ2,5 spectrum are dueto dipole transitions to the Fe 1s core from molecular orbitals thatare primarily ligand 2p in character but mixed with some Fe 4p and,for molecules lacking inversion symmetry, Fe 3d.23 The intensity of the spectral features is related to theamount of Fe np mixing with the ligand valence orbitals.A greater amount of Fe np character leads to strongerlines.23 The calculated spectrum reproducesthe experimental features well. The energy and intensity of the maintransitions contributing along with representations of the molecularorbitals involved are shown. The calculated spectrum was shifted by150 eV to match the experimental spectrum. It can be seen that themolecular orbitals that are probed are those concentrated on the ligandsand that have dominantly p character.


Feasibility of Valence-to-Core X-ray Emission Spectroscopy for Tracking Transient Species.

March AM, Assefa TA, Bressler C, Doumy G, Galler A, Gawelda W, Kanter EP, Németh Z, Pápai M, Southworth SH, Young L, Vankó G - J Phys Chem C Nanomater Interfaces (2015)

Measured ironvalence-to-1s core XES compared with DFT-simulated spectrum. (top)Measured vtc XES of 0.4 M aqueous [Fe(CN)6]4– and the calculated spectrum for the same ion. (bottom) Spectrumof sodium nitroprusside, in solid form, and calculations for the [Fe(CN)5(NO)]2– ion. Representations of the maincontributing molecular orbitals are shown.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4634714&req=5

fig2: Measured ironvalence-to-1s core XES compared with DFT-simulated spectrum. (top)Measured vtc XES of 0.4 M aqueous [Fe(CN)6]4– and the calculated spectrum for the same ion. (bottom) Spectrumof sodium nitroprusside, in solid form, and calculations for the [Fe(CN)5(NO)]2– ion. Representations of the maincontributing molecular orbitals are shown.
Mentions: Roughly 50 eV to higherenergy, on the tail of the core-to-core Kβ1,3 spectrum,is the vtc region which exhibits more sensitivity to the chemicalenvironment of the absorbing metal ion and hence more spectral variationfor different chemical species than core-to-core Kβ. Measuredand calculated vtc spectra of aqueous [FeII(CN)6]4– are shown in the top panel of Figure 2. The intensity is considerably weaker than thatfor the core-to-core Kβ1,3 fluorescence, with a peakcount rate of 130 counts per second as compared to 4200 counts persecond. The features of the Kβ2,5 spectrum are dueto dipole transitions to the Fe 1s core from molecular orbitals thatare primarily ligand 2p in character but mixed with some Fe 4p and,for molecules lacking inversion symmetry, Fe 3d.23 The intensity of the spectral features is related to theamount of Fe np mixing with the ligand valence orbitals.A greater amount of Fe np character leads to strongerlines.23 The calculated spectrum reproducesthe experimental features well. The energy and intensity of the maintransitions contributing along with representations of the molecularorbitals involved are shown. The calculated spectrum was shifted by150 eV to match the experimental spectrum. It can be seen that themolecular orbitals that are probed are those concentrated on the ligandsand that have dominantly p character.

Bottom Line: Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit.In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES for time-resolved experiments.We discuss technical improvements that will make valence-to-core XES a practical pump-probe technique.

View Article: PubMed Central - PubMed

Affiliation: X-ray Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.

ABSTRACT

X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. X-ray absorption spectroscopy (XAS) is considered an established technique for such measurements, and X-ray emission spectroscopy (XES) of the strongest core-to-core emission lines (Kα and Kβ) is now being utilized. Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit. In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES for time-resolved experiments. We discuss technical improvements that will make valence-to-core XES a practical pump-probe technique.

No MeSH data available.