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other products. Thus, the species in components II and III must be robust
and/or chemically inactive.
9.4.3 E
FFECT OF
A
BLATION
L
ASER
P
OWER ON THE
M
ASS
S
PECTRAL
P
ATTERN
In an attempt to identify these long-lived species we examined the effect of
varying ablation laser power on the mass spectral pattern. Figures 9.7 and
9.8
demonstrate the result of experiments using laser powers of 4.0mJ/pulse
and 7.1mJ/pulse. Figure 9.8 is essentially the same as
Figure 9.4
,
but is
reproduced for ease of comparison with Figure 9.7, which shows the result
for the laser power reduced from 7.1mJ/pulse to 4.0mJ/pulse. The com-
parison reveals the following features. First, at a delay time of 35
m
s the
reduction of the power suppressed all the peaks, but the suppression of
the bared carbon clusters was relatively small. Second, the persistence of the
dihydrides and C
10
was observed for the run of the reduced power, as in the
case of the power at 7.1mJ/pulse.
If the observed dihydrides (C
2n
H
2
) were formed by reactions of the
observed C
2n
with the buffer gas, the peaks of C
2n
for the run of the power at
7.1mJ/pulse would be noticeably increased in conformity with the observed
enhancement of C
2n
H
2
. Since there seems no such correlation, the carbon
atoms constituting the dihydrides have to originate from carbon clusters
larger than those recorded in the spectra.
FIGURE 9.7
with a reduced ablation laser power.
TOF mass spectra observed similarly to those in
Figures 9.4
and
9.8
but
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