Interaction of the Chlorine Atom with Water: ESR and ab Initio MO Evidence for
Three-Electron (
2*1) Bonding
Received: December 16, 1996 Revised February 11, 1997 Abstract: The specific interaction of chlorine atoms with water has been
investigated by electron spin resonance
spectroscopy and molecular orbital theory. Chlorine atoms are
formed by attack of hydroxyl radicals on
chloride ions in frozen aqueous solutions at low temperatures. A
variety of frozen aqueous systems were
irradiated at 77 K and investigated by ESR spectroscopy, and results
obtained suggest a localized three-electron bond ( Download the full text:
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and
2*1) between
Cl and H2O or less likely with
OH-. Chlorine atom interactions with
both
species were investigated by both ab initio and semiempirical molecular
orbital calculations. A series of
isolated chlorine-water radical species consisting of hydrated
chlorine atoms as well as chloride anions with
hydroxyl radicals were considered. Best agreement with experiment
is found for chlorine atom-water
interactions,
H2O-
l(H2O)n.
Full optimization ofSKIPOH-Cl-
aquated systems shows that energetic ion dipole
forces overcome weaker * interactions and result in full spin
localization on the hydroxyl radical. Poor
agreement with experiment is found even when the
ClOH- structure is held in position
to promote *
bonding. However, for
H2O-l(H2O)n
(n = 0, 2 and 5 considered) a comparison of the
experimental hyperfine
couplings and spin densities suggested from experiment, i.e., 60% spin
on the chlorine atom, with the results
found from ab initio calculations, gives improved agreement as
n increases, with best agreement found for
n
= 5. The theoretical results support the formation of a
water-chlorine three-electron bond with a substantial
sharing of the unpaired spin between the bonding entities.
