Core-to-Rydberg band shift and broadening of hydrogen bonded ammonia clusters studied with nitrogen K-edge excitation spectroscopy

Yamanaka Takeshi

Tabayashi Kiyohiko

Takahashi Osamu

Tanaka Kenichiro

Namatame Hirofumi

Taniguchi Masaki

Journal of Chemical Physics

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) 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 -> 3sa(1)/3pe of AM monomer are considerably broadened. The changes of the experimental core-to-Rydberg transitions Delta FWHM (N 1s -> 3sa(1)/3pe) = similar to 0.20/similar to 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 center dot center dot center dot 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-sigma* 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 sigma* (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. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3673778]

ammonia

association

binding energy

density functional theory

hydrogen bonds

intermolecular mechanics

molecular clusters

orbital calculations

red shift

resonant states

Rydberg states

spectral line broadening

time of flight mass spectra

X-ray absorption spectra

Chemistry [ 430 ]

eng

The American Institute of Physics

(c) 2012 American Institute of Physics

[ISSN] 0021-9606

[DOI] 10.1063/1.3673778

[NCID] AA00694991

[DOI] http://dx.doi.org/10.1063/1.3673778