Ultrafast dynamics in the excited hydrogen atom transfer states of ammonia clusters

Autor: W. Radloff, Ingolf V. Hertel, P. Farmanara, V. Stert, H.-H. Ritze
Rok vydání: 2002
Předmět:
Zdroj: The European Physical Journal D. 19:193-209
ISSN: 1434-6079
1434-6060
DOI: 10.1140/epjd/e20020071
Popis: Neutral ammonia clusters (NH3)m are photo-excited to the electronic \(\) state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters rearrange to form an H-transfer state (NH3)m-2NH4(3s)NH2 with the subunit NH4 in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength. Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH3)m-2NH4(3p)NH2 states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization. The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast dissociation.
Databáze: OpenAIRE
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