and Tokyo [36]. The black-body radiation is significantly reduced at a few Kelvin,
and the ions will ascertain the trap temperature by radiative cooling after some time.
3.4
Summary
It is important to remember that different instruments are ideal for studying certain
molecular ions and processes. Storage rings for example are beneficial when
dissociation occurs on the tens of microseconds to tens of milliseconds time scale
while for faster dissociation, single-pass instruments like accelerator mass
spectrometers and reflectron time-of-flight instruments are sufficient. Hence spectroscopy of weakly bound complexes, e.g., microsolvated ions, is most easily done
with the latter-type instruments. In general, experiments on high-keV ions have the
advantage that the fragments have high kinetic energies, and both ions and neutrals
can easily be detected.
If high mass resolution is required, ion traps where the measurements do not rely
on ion velocity, such as Penning traps, are superior. However, time-resolved
experiments cannot easily be done on the tens of microseconds time scale with an
FT-ICR instrument as cyclotron frequencies are too small for enough cycles in the
time window to do a proper Fourier transform of the time spectrum to a frequency
spectrum (mass-to-charge spectrum). This time scale is therefore best investigated
with storage-ring instruments or the Zajfman trap.
In general dissociation on a long time scale (tens of milliseconds) is problematic
as radiative cooling can quench the dissociation. Multiple photon absorption can
therefore be required to observe dissociation within the sampling time. Furthermore, when the dissociation time scale is long, it is particularly important to be
aware of kinetic shifts as the identification of low-energy photon absorption is
disfavoured when the dissociation is sampled in a finite time window. In ion traps
Fig. 3.21 The double
electrostatic ion beam storage
ring (DESIREE) in
Stockholm [35]. An ion beam
of one charge is injected into
one ring, while one of
opposite charge is injected
into the other. The beams
merge in the common straight
central section and their
interaction studied. The inner
vacuum chamber and
electrostatic elements are kept
at cryogenic temperature.
Figure kindly provided by
Henrik Cederquist
(Stockholm University)
3 Experimental Techniques
41
and the ions will ascertain the trap temperature by radiative cooling after some time.
3.4
Summary
It is important to remember that different instruments are ideal for studying certain
molecular ions and processes. Storage rings for example are beneficial when
dissociation occurs on the tens of microseconds to tens of milliseconds time scale
while for faster dissociation, single-pass instruments like accelerator mass
spectrometers and reflectron time-of-flight instruments are sufficient. Hence spectroscopy of weakly bound complexes, e.g., microsolvated ions, is most easily done
with the latter-type instruments. In general, experiments on high-keV ions have the
advantage that the fragments have high kinetic energies, and both ions and neutrals
can easily be detected.
If high mass resolution is required, ion traps where the measurements do not rely
on ion velocity, such as Penning traps, are superior. However, time-resolved
experiments cannot easily be done on the tens of microseconds time scale with an
FT-ICR instrument as cyclotron frequencies are too small for enough cycles in the
time window to do a proper Fourier transform of the time spectrum to a frequency
spectrum (mass-to-charge spectrum). This time scale is therefore best investigated
with storage-ring instruments or the Zajfman trap.
In general dissociation on a long time scale (tens of milliseconds) is problematic
as radiative cooling can quench the dissociation. Multiple photon absorption can
therefore be required to observe dissociation within the sampling time. Furthermore, when the dissociation time scale is long, it is particularly important to be
aware of kinetic shifts as the identification of low-energy photon absorption is
disfavoured when the dissociation is sampled in a finite time window. In ion traps
Fig. 3.21 The double
electrostatic ion beam storage
ring (DESIREE) in
Stockholm [35]. An ion beam
of one charge is injected into
one ring, while one of
opposite charge is injected
into the other. The beams
merge in the common straight
central section and their
interaction studied. The inner
vacuum chamber and
electrostatic elements are kept
at cryogenic temperature.
Figure kindly provided by
Henrik Cederquist
(Stockholm University)
3 Experimental Techniques
41