Bond rearrangement during molecular dissociation; a sudden or slow process?

M. Sayler, D. Hathiramani, K.D. Carnes, B.D. Esry, I. Ben-Itzhak
J.R. Macdonald Laboratory, Department of Physics, Kansas State University

Bond-rearrangement during molecular dissociation leads to the formation of molecules from atoms not directly bound in the precursor molecule. One such process is the decay of the transient H₂O⁺ ion into H₂⁺ + O, which requires the formation of a H-H bond during dissociation. It is important to determine if the new bond is formed during the slow dissociation or if the system makes a sudden transition between the initial and final bound states. Intuitively one would expect heavier isotopes to dissociate slower, and thus the bonds would rearrange easier if the first mechanism dominates. We measured the hydrogen molecular ion formation rate from H₂O, HDO and D₂O bombarded by fast ions, and found that it depends strongly on the fragment mass. This suggests that the rearrangement does not happen during the slow dissociation, but rather during the very fast ionization. Calculations are underway to determine the relative production rates for the different isotopes from the overlap of the initial and final vibrational wave functions. Preliminary measurements indicate that the transient H_2O^2+ ion decays also to H₂⁺ + O⁺; the question is if it shows a similar isotopic dependence as predicted by sudden bond rearrangement.

This work was supported by the Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Submitted to DAMOP 2002, May 2002 in Williamsburg, VA.

 

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