15min:
VIBRATIONAL PREDISSOCIATION DYNAMICS OF THE (H2O)2 DIMER.

L. C. CH'NG, B. E. ROCHER, A. K. MOLLNER AND H. REISLER, Department of Chemistry, University of Southern California, Los Angeles, CA, 90089.

The state-to-state vibrational predissociation dynamics of the (H2O)2 dimer were studied by resonance-enhanced multiphoton ionization (REMPI) and velocity-map imaging (VMI) to obtain pair-correlated product energy distributions. The 2+1 REMPI spectra of the H2O photofragments were recorded via the C1B1 (000) leftarrow X1A1 (000 and 010) transition following a vibrational excitation of the dimer’s bound-OH stretch fundamental. The fragment’ center-of-mass translational energy (c.m. E T) distributions were determined from VMI of selected rotational states of the detected H2O photofragments. The c.m. E T distributions were then converted to pair-correlated H2O cofragment rotational level distributions. This is the first experiment in which H2O products with bend ( nu2) excitation were observed by REMPI. The dissociation energy of the dimer was determined from the images with spectroscopic accuracy. The predissociation mechanism of (H2O)2 will be discussed and compared with the corresponding hydrogen bonded dimers of an acid (HCl-H2O) and a base (NH3-H2O).