| Autor: |
Farmanara, P., Ritze, H.-H., Stert, V., Radloff, W., Hertel, I. V. |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 1/22/2002, Vol. 116 Issue 4, p1443, 14p, 5 Diagrams, 2 Charts, 11 Graphs |
| Abstrakt: |
The energetics and ultrafast dynamics in the H atom transfer configuration of ammonia dimer and trimer clusters have been studied. The clusters are first excited to the electronic A˜ state with a 208 nm femtosecond laser pump pulse. This state is allowed to relax for about 1 ps during which the H-transfer state is formed which is then electronically excited by a time-delayed infrared control pulse at 832 nm and finally ionized with a third femtosecond probe pulse at 416 nm. We have also performed complementary theoretical studies elucidating the experimental findings. For the dimer in the excited NH[sub 4](3p)...NH[sub 2](X˜) state the time-dependent ion signals reveal an isotope-independent short lifetime of about τ[sub 6]=(130±60) fs which can be explained by a curve crossing with the repulsive NH[sub 4](3s)...NH[sub 2](A˜) state, whereas the trimer signal persists on a time scale being more than one order of magnitude longer and exhibits a very large isotope effect. This is interpreted as being due to internal conversion from the excited state NH[sub 3]NH[sub 4](3p)...NH[sub 2](X˜) back to the NH[sub 3]NH[sub 4](3s)...NH[sub 2](X˜) ground state. The analysis of the corresponding photoelectron spectra also confirms the transition energies between the electronic states involved, e.g., ΔE[NH[sub 4](3s→3p)...NH[sub 2]]=1.5 eV and ΔE[NH[sub 3]NH[sub 4](3s→3p)...NH[sub 2]]=1.2 eV, as determined by our ab initio calculations. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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