This describes a study of some unusual features of the hydrated electron, [symbol omitted] in particular the kinetics of its decay during a period of non-homogeneity lasting tens of nanoseconds, the formation
and photodissociation of a hydrated dielectron species [symbol omitted], and the
photoexcitation of [symbol omitted].
Nanosecond pulse radiolysis (p.r.) studies on the kinetic behaviour
of [symbol omitted](> 10⁻⁴ M) in pure deaerated water revealed a complicated
interplay of mechanisms for the first half life ∼110 nsec. This is
partly attributable to an initial non-homogeneity in the distribution of
reacting species within the system, because the spurs are essentially
isolated for tens of nanoseconds. Calculations based on a qualitative
model revealed that the times necessary for spur-overlap through diffusion
(during which > 40% [symbol omitted] were lost to reaction) were in agreement with
experimental observations. However the anomalous trends in κ, a rate
parameter describing [formula omitted] within this period, led to the subsequent
discovery of a process by which [symbol omitted] were formed after the electron pulse.
The use of selective ion and radical scavengers strongly implied that the
increase in [symbol omitted] occurred via another radiolytic product, XB. Three
plausible mechanisms have been outlined in which XB is (e_ ) [formulae omitted]. XB undoubtedly affects the values of κ but it is not possible at this time to discard the notion of microscopic non-homogeneity within the spur itself as the trends in κ might suggest.
Four conclusions are drawn; (i) in some p.r. studies we may not
calculate meaningful second order rate constants with concentrations
evaluated from optical density data, (ii) the "instantaneous" yield of
[symbol omitted] seen through nsec p.r. is higher than that established through
μsec p.r. or steady-state techniques because of the rapid initial loss
of [symbol omitted] (iii) but the total [symbol omitted] yield will be less since the latter
techniques cannot distinguish the source of [symbol omitted]. (iv) there is a
critical need for a nanosecond p.r. yield of [symbol omitted] to establish the true
primary yield, [symbol omitted].
Some microsecond flash photolysis (f.p.) experiments were
performed on hydrogen saturated alkaline solutions. Hydrated electrons
were produced following the ultra-violet photolysis of OH⁻ and reacted
bimolecularly to give a species which on subsequent infra-red flash
photolysis regenerated [symbol omitted]. This species is postulated to be a
hydrated electron dimer [formula omitted] the spin state of which is unspecified
The remaining purpose of this work was to photoexcite [symbol omitted]. The
nature of the excited state of [symbol omitted] and the origin of the optical
absorption band is still open to speculation although Jortner and others
have performed calculations in which the transition at λmax is assigned
to a 2p + 1s excitation. The photolysis of [symbol omitted] was attempted through
both p.r. and f.p. techniques, neither of which yielded any conclusive
information because of the presence of XB or [symbol omitted] in the system. / Science, Faculty of / Chemistry, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/34730 |
| Date | January 1970 |
| Creators | Kenney, Geraldine Anne |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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