Core-to-Rydberg band shift and broadening of hydrogen bonded ammonia clusters studied with nitrogen K-edge excitation spectroscopy
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Nitrogen 1s (N ls) core-to-Rydberg excitation spectra of hydrogen-bonded clusters of ammonia (AM) have been studied in the small cluster regime of beam conditions with time-of-flight (TOF) fragmentmass spectroscopy. By monitoring partial-ion-yield spectra of cluster-origin products, “cluster” specific excitation spectra could be recorded. Comparison of the “cluster” band with “monomer” band revealed that the first resonance bands of clusters corresponding to N 1s→3sa1/3pe of AM monomer are considerably broadened. The changes of the experimental core-to-Rydberg transitions Δ FWHM (N 1s → 3sa1/3pe) = ∼0.20/∼0.50 eV compare well with the x ray absorption spectra of the clusters generated by using density functional theory (DFT) calculation. The broadening of the core-to-Rydberg bands in small clusters is interpreted as being primarily due to the splitting of non-equivalent core-hole N 1s states caused by both electrostatic core-hole and hydrogen-bonding (H3N···H–NH2) interactions upon dimerization. Under Cs dimer configuration, core-electron binding energy of H−N (H-donor) is significantly decreased by the intermolecular core-hole interaction and causes notable redshifts of core-excitation energies, whereas that of lone-pair nitrogen (H-acceptor) is slightly increased and results in appreciable blueshifts in the core-excitation bands. The result of the hydrogen-bonding interaction strongly appears in the n−σ* orbital correlation, destabilizing H−N donor Rydberg states in the direction opposite to the core-hole interaction, when excited N atom with H−N donor configuration strongly possesses the Rydberg component of anti-bonding σ* (N−H) character. Contributions of other cyclic H-bonded clusters (AM)n with n ≥ 3 to the spectral changes of the N 1s → 3sa1/3pe bands are also examined.
The present study was performed under the Cooperative Research Program (Nos. #07-A-58 and #08-A-51) of HiSOR, at HSRC, Hiroshima University. The present work was partly supported by a grant-in-aid for scientific research (B) from the MEXT (Grant No. 21350014).
O. Takahashi is grateful for the financial support from a grant-in-aid for scientific research from JSPS of Japan (Grant No. 23540476).
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Copyright (c) 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in J. Chem. Phys. 136, 014308 (2012) and may be found at https://doi.org/10.1063/1.3673778.
Graduate School of Science
Hiroshima Synchrotron Radiation Center
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