Transcript Cluster Beam FT-ICR-MS

fullerene-coated
graphite target rod
Cluster Source Block
Valve emits a helium
pulse
Nd:YAG laser (532
nm, 3-5 ns, 5mj/pulse)
vaporises the target
rod by a single
pulse/shot
Fullerenes react with
carbon vapor (C,
C2) in the “clustering
zone”. Then, the gas
exits the channel
and undergoes a
supersonic
expansion to create
a cooled, molecular
beam
The rod is continuously translated and rotated by a
stepper motor
stepper target
accumulation
motor
rod skimmer
octopole
pulsed
valve
transfer
octopole
source
10-7 torr
10-7
10-8
10-10
diffusion pump
turbo
pump
turbo
pump
turbo
pump
ICR
cell
pulsed
valve
Fullerenes react
with carbon
species in the
vapourisation
zone, then exit
reaction
channel
the ions which
…undergo enter the ion
supersonic optics, where
expansion they are
acuumulated
and are
in the central
skimmed
into beam octopole
segment
10-7 torr
diffusion pump
10-7
turbo
pump
10-8
turbo
pump
After 3-10 single laser shot accumulations, the
ions are transferred to the ICR cell, which is
located within in the bore of a 9.4 tesla
superconducting magnet. Under the influence
of the high magnetic field, the ions exhibit
cyclotron motion. The ions induce a current on
electrodes, which is detected as an “image
current” in the time domain, and then the
signal is converted to the frequency domain
by an FT. Thus, the mass of the ion is detected
as a frequency.
10-10
turbo
pump
Answer to questions from email.
Q: How do you stop the pulse of ions in the
accumulation trap
A: The ions are confined radially by an oscilating
radiofrequency within in octopole, and axially by
voltages at the ends of the “accumulation octopole:.
Answer to questions from email.
Q: How many pulses do you need to accumulate?
A: A single laser shot is used vaporize the target during a
single Helium pulse. Ten singe laser shot + He pulse are
used to accumulate ions.
Q:How do you decide when to transfer them.
A: After the final laser shot, a voltage at the “back” of
the accumulation octopole switched, and the ions are
transferred to the ICR cell. The switching of the voltage is
controlled by the computer program interface.
Q: How many runs do you need in general for an
average result?
A: 3 time-domain aquisitions are averaged for when
“growing” a preformed fullerene…….the signal is
extremely strong.
And 10 time-domain acquisitions are averaged when
form endohedrals from a graphite-metal target.
Thus, up to 10 time-domain acquisitions are averaged.
Fullerenes react with carbon vapor in the “clustering
zone”, then the gas exits the channel and undergoes a
supersonic expansion.
As the clusters move from a region of high pressure
through a small orifice into a high vacuum, they
undergo a supersonic expansion. The random thermal
energy of the clusters is converted into a directed
motion (creating a cooled, molecular beam in which
very few collisions occur) toward the skimmer and the
ions subsequently enter the ion optics where they are
accumulated and then transferred to the ICR cell for
detection.