Size-Dependent Velocity Map Photoelectron Imaging of Nanosized Ammonia Aerosol Particles
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  • 作者:Adam H. C. West ; Bruce L. Yoder ; Ruth Signorell
  • 刊名:Journal of Physical Chemistry A
  • 出版年:2013
  • 出版时间:December 19, 2013
  • 年:2013
  • 卷:117
  • 期:50
  • 页码:13326-13335
  • 全文大小:393K
  • 年卷期:v.117,no.50(December 19, 2013)
  • ISSN:1520-5215
文摘
The size dependence of the band position, the bandwidth, and the asymmetry parameter in the valence photoelectron spectrum of ammonia clusters and ultrafine ammonia aerosol particles is investigated for aggregates with diameters up to 7 nm. The neutral aggregates are ionized by single photons at 13.318 eV from a tabletop vacuum ultraviolet laser. The photoelectrons are detected in a velocity map imaging photoelectron spectrometer. The size distributions of the neutral aggregates are determined independently using the Na-doping method. Up to clusters with a few tens of molecules, the first ionization energy (value at band maximum) decreases, the width of the lowest band in the photoelectron spectrum broadens, and the corresponding asymmetry parameter decreases with increasing cluster size. Constant (鈥減lateau鈥? values of these parameters are found for larger aggregates, which might be explained by a predominantly noncrystalline structure of these aggregates with an average coordination similar to that of the liquid. This explanation is in agreement with previous infrared studies and theoretical predictions.

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