ABSTRACT

NH₄  is a typical hypervalent radical and is short lived, but it is stabilized extensively in the gase-phase clusters. The physical and chemical properties of NH₄ and  NH₄ (NH₃)_n have been the subject of intensive studies. In the present paper, the formation and decay dynamics of ammoniated NH₄ are discussed on the basis of on the femtosecond pump-probe experiments. The mechanism of the stabilization of this radical in ammonia clusters is also discussed using the results on the successive binding energies of these clusters. The absorption spectra of NH₄ (NH₃)_n, exhibiting strong size dependence, are ascribed to a spontaneous ionization of NH₄  in ammonia clusters. The large enhancement of the nonradiative decay rate in the first excited state of these clusters are discussed in relation to the extensive reduction of the excitation energy due to the spontaneous ionization and the delocalization of valence electron.