GFP chromophore anion in the gas phase. Various ion storage techniques, including
electrostatic storage rings [29, 30], quadrupole ion traps [10, 31] and ion cyclotron
resonance cells [32], along with detection of both ionic [10, 31] and neutral
fragments [29, 30], as well as parent ions loss [10, 31, 32] after photoexcitation
have been used. However, several precautions should apply when using a
photoresponse of these chromophores for retrieving their absorption profiles. In
particular, a multiple photon absorption and an electron autodetachment channel in
the case of anions have to be taken into account. Measurements by the Toronto
group [10, 31] showed loss of stored chromophore ions after photoexcitation that
could not be accounted for by the recorded ionic fragments. This loss was suggested
to be due to electron detachment which would produce undetectable neutral
chromophores that are lost from the ion trap. Moreover, structures in the ion-loss
signal was observed, the origin of which might be related to the influence of
vibrations. Recent photoelectron spectroscopy studies have directly confirmed
that electron emission is one of the deactivation channels in the bare anion
[33–35]. Experiments carried out by the Zurich group [32] also bring up a discussion of the effect of multiple photon absorption and suggest that an intrinsic
absorption maximum is blue-shifted compared to earlier results, even though
such a conclusion was drawn in the case of ions trapped up to 200 s with an
unknown impact of IR radiative cooling on the observed absorption profiles.
A persistent interest in the action spectroscopy of the pHBDI anion underscores
an enriched intrinsic photo-induced dynamics of the chromophore as well as
difficulties in correct interpretation of the results reported hitherto. The reliability
of action spectroscopy in revealing the absorption profiles of the bare GFP chromophore anion is one of the most important issues. We highlight a recent progress in
studying the intrinsic photoresponse of the chromophore by introducing timeresolved measurements based on the new experimental detection techniques,
where one is able to record action spectra according to the timescale at which the
action takes place. Thus, neutral products belonging to prompt electron emission as
well as delayed ones are now detected separately. When combined with theoretical
account of observed action spectra, this new time-domain approach based on direct
detection, in which spectral properties of the two different channels are simultaneously, but separately recorded, enables to disclose mechanisms of intrinsic
excited-state decay channels in the GFP chromophore anion.
5.2
Time-Resolved Action Spectroscopy
5.2.1 Prompt and Delayed Action at ELISA
We wish to be able to register the event of a photon being absorbed by a molecule.
The technique that has been developing for this over the years involves registration
of some form of ‘action’; hence the name is action spectroscopy. The action is
typically a break-up of the molecule (fragmentation), or in the case of an anion, it
may be the emission of an electron. In action spectroscopy, molecular fragments, or
72
A.V. Bochenkova and L.H. Andersen
electrostatic storage rings [29, 30], quadrupole ion traps [10, 31] and ion cyclotron
resonance cells [32], along with detection of both ionic [10, 31] and neutral
fragments [29, 30], as well as parent ions loss [10, 31, 32] after photoexcitation
have been used. However, several precautions should apply when using a
photoresponse of these chromophores for retrieving their absorption profiles. In
particular, a multiple photon absorption and an electron autodetachment channel in
the case of anions have to be taken into account. Measurements by the Toronto
group [10, 31] showed loss of stored chromophore ions after photoexcitation that
could not be accounted for by the recorded ionic fragments. This loss was suggested
to be due to electron detachment which would produce undetectable neutral
chromophores that are lost from the ion trap. Moreover, structures in the ion-loss
signal was observed, the origin of which might be related to the influence of
vibrations. Recent photoelectron spectroscopy studies have directly confirmed
that electron emission is one of the deactivation channels in the bare anion
[33–35]. Experiments carried out by the Zurich group [32] also bring up a discussion of the effect of multiple photon absorption and suggest that an intrinsic
absorption maximum is blue-shifted compared to earlier results, even though
such a conclusion was drawn in the case of ions trapped up to 200 s with an
unknown impact of IR radiative cooling on the observed absorption profiles.
A persistent interest in the action spectroscopy of the pHBDI anion underscores
an enriched intrinsic photo-induced dynamics of the chromophore as well as
difficulties in correct interpretation of the results reported hitherto. The reliability
of action spectroscopy in revealing the absorption profiles of the bare GFP chromophore anion is one of the most important issues. We highlight a recent progress in
studying the intrinsic photoresponse of the chromophore by introducing timeresolved measurements based on the new experimental detection techniques,
where one is able to record action spectra according to the timescale at which the
action takes place. Thus, neutral products belonging to prompt electron emission as
well as delayed ones are now detected separately. When combined with theoretical
account of observed action spectra, this new time-domain approach based on direct
detection, in which spectral properties of the two different channels are simultaneously, but separately recorded, enables to disclose mechanisms of intrinsic
excited-state decay channels in the GFP chromophore anion.
5.2
Time-Resolved Action Spectroscopy
5.2.1 Prompt and Delayed Action at ELISA
We wish to be able to register the event of a photon being absorbed by a molecule.
The technique that has been developing for this over the years involves registration
of some form of ‘action’; hence the name is action spectroscopy. The action is
typically a break-up of the molecule (fragmentation), or in the case of an anion, it
may be the emission of an electron. In action spectroscopy, molecular fragments, or
72
A.V. Bochenkova and L.H. Andersen