Chapter 12
Charge Transfer and the Harpoon
Mechanism
12.1 Introduction
An important concept in the interaction of metals with nonmetal atoms/molecules is
that of charge transfer (CT). The charge-transfer reactivity is extensively investigated
and mostly seen for an ion/neutral species reaction in which the total charge on the
reactant ion is transferred initially to the reactant neutral species so that the reactant
ion becomes a neutral entity [1–38] Some of the possible reactions of ions M
2+ , M
+
and M
− with a neutral species Y are categorized in terms of the above definitions as
follows [39]:
M
2+
+ Y → M
+
+ Y
+
(Partial charge transfer)
(12.1)
M
+
+ Y → M
2+
+ Y + e
−
(Charge stripping)
(12.2)
M
−
+ Y → M
+
+ Y + 2e
−
(Charge stripping & charge inversion)
(12.3)
These are all ion/neutral species reactions and charge permutation reactions.
Besides, transient CT states frequently show up when two gas-phase species collide
with each other; the CT process may lead to chemical reactions when there is a
suitable difference in the electron affinity and ionization potential of the colliding
species. Such reactivity is examined in terms of harpoon-type reactions between
alkali-metal atoms and halogen molecules, where the harpoon mechanism is demonstrated to allow for a largely increased reactive cross section due to the valence
electron transfer from the alkali metal atom (M) to the halogen molecule (X 2 ),
M + X 2 →
M
+
+ X
−
2 →
MX + X (Harpoon mechanism)
(12.4)
The Sect. 12.3 is partly reproduced from Chem. Phys. Lett., 2013, 590, 63–68.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity,
https://doi.org/10.1007/978-981-15-9704-6_12
193
Charge Transfer and the Harpoon
Mechanism
12.1 Introduction
An important concept in the interaction of metals with nonmetal atoms/molecules is
that of charge transfer (CT). The charge-transfer reactivity is extensively investigated
and mostly seen for an ion/neutral species reaction in which the total charge on the
reactant ion is transferred initially to the reactant neutral species so that the reactant
ion becomes a neutral entity [1–38] Some of the possible reactions of ions M
2+ , M
+
and M
− with a neutral species Y are categorized in terms of the above definitions as
follows [39]:
M
2+
+ Y → M
+
+ Y
+
(Partial charge transfer)
(12.1)
M
+
+ Y → M
2+
+ Y + e
−
(Charge stripping)
(12.2)
M
−
+ Y → M
+
+ Y + 2e
−
(Charge stripping & charge inversion)
(12.3)
These are all ion/neutral species reactions and charge permutation reactions.
Besides, transient CT states frequently show up when two gas-phase species collide
with each other; the CT process may lead to chemical reactions when there is a
suitable difference in the electron affinity and ionization potential of the colliding
species. Such reactivity is examined in terms of harpoon-type reactions between
alkali-metal atoms and halogen molecules, where the harpoon mechanism is demonstrated to allow for a largely increased reactive cross section due to the valence
electron transfer from the alkali metal atom (M) to the halogen molecule (X 2 ),
M + X 2 →
M
+
+ X
−
2 →
MX + X (Harpoon mechanism)
(12.4)
The Sect. 12.3 is partly reproduced from Chem. Phys. Lett., 2013, 590, 63–68.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity,
https://doi.org/10.1007/978-981-15-9704-6_12
193