Real time observation of hydrogen transfer: Femtosecond time-resolved photoelectron spectroscopy in the excited ammonia dimer
作者:P. Farmanara、W. Radloff、V. Stert、H.-H. Ritze、I. V. Hertel
DOI:10.1063/1.479343
日期:1999.7.8
The energy flow in ammonia dimers excited to the electronic à state is analyzed by combining the femtosecond pump–probe technique and the photoelectron–photoion coincidence detection. We use ∼140 fs laser pulses (200 nm for excitation and 267 nm for ionization). For the dimer ion the photoelectron spectra change drastically from a rather broad shape (≳1 eV) at small delay times between pump and probe pulse to a rather narrow peak (0.25 eV) at some picoseconds. This is explained by the dynamics of an internal H-atom transfer in the electronic à state to an NH4…NH2 configuration. The measured photoelectron energies are consistent with ab initio potential energy surface calculations. The observed picosecond lifetime of the hydrogen-transfer state NH4…NH2 can be understood by a conical intersection with the charge-transfer state NH4+…NH2−.