Photodetachment of F-(H2O)n (n=1-4):: Observation of charge-transfer states [F-(H2O)n+] and the transition state of F+H2O hydrogen abstraction reaction

We report a photoelectron spectroscopic study of F-(H2O)(n) (n=1-4) at 193 and 157 nm. In addition to a detachment feature from F-, we observed a higher binding energy feature in all spectra due to ionization of the solvent molecules leading to F-(H2O)(n)(+) charge-transfer states. Detachment of an electron from F- in F-(H2O) reaches the transition state region of the reaction, F+H2O --> HF+OH. The bound to non-bound transition resulted in a long tail at the low binding energy side in the photoelectron spectrum of F-(H2O). We estimated that the neutral F . . .H2O complex at the anion geometry, which is near the transition state region of the H-abstraction reaction, is 6 +/-1 kcal/mol above the F+H2O asymptote, consistent with a previous estimation of a 4 kcal/mol entrance barrier height for this reaction. (C) 2001 American Institute of Physics.