CARINE MANCA, MARTIN QUACK, MARTIN WILLEKE, Physical chemistry, ETH Zurich, 8093 Zurich, Switzerland.

The hydrogen fluoride dimer (HF)2 is widely used as prototype system to describe and model dynamics in hydrogen bonded systems. This dimer has the advantage to be particularly ''simple'' and therefore allows for both high-resolution rovibrational spectroscopy\footnoteT. R. Dyke, B. J. Howard, W. J. Klemperer, J. Chem. Phys. , \textbf1972, 56 , 2442. A. S. Pine, W. J. Lafferty, J. Chem. Phys. \textbf1983, 78 , 2154. K. von Puttkamer, M. Quack, Mol. Phys. , \textbf1987, 62 , 1047; K. von Puttkamer, M. Quack, Chem. Phys. , \textbf1989, 139 , 31. M. Quack, M. Suhm, Chem. Phys. Lett. , \textbf1990, 171 , 517. M. Quack, M. Suhm, J. Chem. Phys. , \textbf1991, 95 , 28.,\footnoteM. Hippler, L. Oeltjen, M. Quack, to be published ; M. Quack, Chimia , \textbf2003, 57 , 147. and full dimensional quantum dynamical calculations on accurate potential hypersurfaces\footnoteW.~Klopper, M. Quack, M. Suhm, J. Chem. Phys. , \textbf1998, 108 , 10096; M. Quack, M. Suhm, In Advances in Molecular Vibrations and Collision Dynamics , \textbf1998, 3 , 205 (and citations therein). M. Quack, M. Suhm. In Conceptual Perspectives in Quantum Chemistry, Conceptual Trends in Quantum Chemistry, Vol. III , J.-L. Calais and E. S. Kryachko, editors, Kluwer Academic Publishers, Dordrecht, \textbf1997, 415. J. Blumberger, L. Oeltjen, M. Quack, Z. Bacić, Y. Qiu, to be published .. An interesting property and a real challenge for experimentalists and theoreticians is the investigation of the mode selectivity of the predissociation dynamics as well as the relative intensities in the spectra. For instance, using highly resolved pulsed jet CW cavity-ring down experimentsb, we have shown that the lifetime of the 21 state involving two quanta of the bonded HF stretching mode is only sim 50~ps whereas that of the 22 state involving two quanta of the free HF stretching mode is more than 1~ns. The 23 state exhibits an intermediate behavior ( tau_\mathrmPD simeq 200~ps).

In this paper, we study the vibrational predissociation in the HF dimer with classical trajectory calculations using the accurate fully 6D SO-3 electronic potential hypersurface established previously in our groupc. Our goal is to obtain a more detailed understanding of the dynamics in this dimer and to provide a benchmark investigation for classical dynamics simulations. We present here our results of lifetimes and absorption spectra for N=1,2,3 polyads of the HF stretching modes and compare them with experimental results.