title: Core-to-Rydberg band shift and broadening of hydrogen bonded ammonia clusters studied with nitrogen K-edge excitation spectroscopy.
abstract: Nitrogen 1s (N 1s) 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) fragment-mass 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 → 3sa(1)/3pe of AM monomer are considerably broadened. The changes of the experimental core-to-Rydberg transitions ΔFWHM (N 1s → 3sa(1)/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 (H(3)N···H-NH(2)) 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 → 3sa(1)/3pe bands are also examined.
authors.affiliation: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamanaka
authors.forename: Kiyohiko
authors.initials: K
authors.lastname: Tabayashi
authors.forename: Osamu
authors.initials: O
authors.lastname: Takahashi
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Tanaka
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Namatame
authors.forename: Masaki
authors.initials: M
authors.lastname: Taniguchi
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D006860:Hydrogen Bonding; D009584:Nitrogen / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D000641:Ammonia; D009584:Nitrogen