Ultrafast photo-excitation dynamics in isolated, neutral water clusters.

Using the efficient nonlinear conversion scheme which was recently developed in our group [M. Beutler, M. Ghotbi, F. Noack, and I. V. Hertel, Opt. Lett. 134, 1491 (2010); M. Ghotbi, M. Beutler, and F. Noack, ibid 35, 3492 (2010)] to provide intense sub-50 fs vacuum ultraviolet laser pulses we have performed the first real time study of ultrafast, photo-induced dynamics in the electronically excited Ã-state of water clusters (H(2)O)(n) and (D(2)O)(n) , n=2-10. Three relevant time scales, 1.8-2.5, 10-30, and 50-150 fs, can be distinguished which-guided by the available theoretical results-are attributed to H (D)-ejection, OH (OD) dissociation, and a nonadiabatic transition through a conical intersection, respectively. While a direct quantitative comparison is only very preliminary, the present results provide a crucial test for future modeling of excited state dynamics in water clusters, and should help to unravel some of the many still unresolved puzzles about water.