Chemistry Reference
In-Depth Information
Fig. 9.7 a Typical trajectory of the STM tip when it tracks a [001]-complex (H
2
O-OH) at
V
s
= 453 mV and I
t
= 0.5 nA. The red and blue lines indicate the displacements along the [110]
and [001] directions, respectively. b The hopping rates of a [001]-complexes as a function of bias
voltage. The red circles and blue squares represent the rates for an H
2
O-OH and D
2
O-OD
complexes, respectively. The tunneling current was fixed at 0.5 nA during the measurements. The
inset shows the result for a D
2
O-OD complex with the tunneling current of 20 nA. c The current
dependence of the hopping rate measured at V
s
= 443 and 343 mV for an H
2
O-OH and D
2
O-OD
complexes, respectively. The reaction orders are 1.1 ± 0.1 and 2.0 ± 0.1 for an H
2
O-OH and
D
2
O-OD complexes, respectively, indicating the hopping is induced via one- and two-electron
processes
(457 meV[
23
]), suggesting that the free O-H stretching is associated with the
process. It is noted that the deuterated complex is immobile at I
t
= 0.5 nA even at
V
s
= 450 mV and it requires a relatively high current (* 20 nA) to induce the
hopping. The current dependence of the rate (Fig.
9.7
c) indicates that the hopping is
induced via one- and two-electron processes for H
2
O-OH and D
2
O-OD complexes,
respectively. The hopping is induced through anharmonic coupling of the m(OH)
with the complex-substrate hindered translation mode. The higher reaction order
for
a
D
2
O-OD
presumably
suggests
that
the
overtone
excitation
of m(OD)
(*660 meV) is required to be overcome the hopping barrier.
