We present two-color fs pump-probe spectra of ${\mathrm{N}\mathrm{a}}_2\mathrm{F}$ which were recorded by employing excitation wavelengths around 1208 nm (pump) and ionization wavelengths around 405 nm (probe). The observed oscillatory structure of the signal with a period of 185 fs shows an excellent agreement with our simulated spectra. The employed ab initio Wigner distribution approach provides clear evidence that this observation is caused by photoinduced metal bond breaking followed by a butterfly-type periodic geometric rearrangement.

• Received 3 June 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.213404