rate constant reproduces the observed decay time of the SF channel. It also explains
why no delayed one-photon signal is observed. The associated lifetime is much too
long and there is basically no decays in the time-interval of observation. This
illustrates very well that the order of absorption, single versus multiple-photon, is
largely dictated by the time-window of observation in the experiment. By studying
sub-ms action one basically avoids problems with radiative cooling of the hot
intermediate molecules. With an instrument, where tens-of-seconds components
are monitored (for example, for n ¼ 1 absorption), one would have to consider the
loss of action (dissociation) due to infrared cooling.
5.3
Time-Resolved Action and Photoelectron Spectra
In the following, the experimental spectroscopic data for the isolated GFP chromophore anion will be discussed. We first consider the spectral region near the first
electronically excited state (S 1 ), where both prompt and delayed action are
observed. Then, additional information is obtained by also considering our photoelectron measurements at a variety of different wavelengths within and beyond the
S 1 spectral region [35].
5.3.1 Action Spectra Near the S 1 State
The action spectra of absorption for the deprotonated GFP chromophore near the S 1
state are shown in Fig. 5.11. The lower graph shows the spectrum for the delayed
signal of the MCP (see Fig. 5.8). The maximum of absorption (482 nm) is in good
agreement with earlier measurements at ELISA (479 nm) [29] and the recent
measurement in a quadrupole-ion trap (482.5 nm) [10].
The upper graph shows the prompt spectrum of the SED (Fig. 5.8). It is seen that
the data (prompt and delayed) have a maximum at the same wavelength (482 nm).
The prompt spectrum has major adjacent shoulders to the blue side of the main peak
at 452 nm and 422 nm and a weak one at 472 nm. Similar features were observed at
the quadrupole ion trap [10, 31] with almost the same wavelength assignments
(470, 450 and 425 nm). The identical peak position in the prompt and delayed
channels at 482 nm strongly indicates that we are addressing the same S 1 state
through two different decay channels.
It is important to note that there is a substantial contribution from a multiplephoton absorption to the main peak of the prompt spectrum. By comparing the red
side of the prompt and delayed spectra, it is realised that heating by one or two
(multiple) photons does not alter much the absorption near threshold energies for
this chromophore. This can easily be rationalised in terms of sequential resonant
absorptions. The absorption of the second photon at a given wavelength can only be
possible if the first photon is absorbed. Thus, the probability of sequential
absorptions is defined as a product of independent probabilities. If we assume
vanishing spectral overlap of individual absorptions before and after heating by
5 Photo-initiated Dynamics and Spectroscopy of the Deprotonated Green. . .
81
why no delayed one-photon signal is observed. The associated lifetime is much too
long and there is basically no decays in the time-interval of observation. This
illustrates very well that the order of absorption, single versus multiple-photon, is
largely dictated by the time-window of observation in the experiment. By studying
sub-ms action one basically avoids problems with radiative cooling of the hot
intermediate molecules. With an instrument, where tens-of-seconds components
are monitored (for example, for n ¼ 1 absorption), one would have to consider the
loss of action (dissociation) due to infrared cooling.
5.3
Time-Resolved Action and Photoelectron Spectra
In the following, the experimental spectroscopic data for the isolated GFP chromophore anion will be discussed. We first consider the spectral region near the first
electronically excited state (S 1 ), where both prompt and delayed action are
observed. Then, additional information is obtained by also considering our photoelectron measurements at a variety of different wavelengths within and beyond the
S 1 spectral region [35].
5.3.1 Action Spectra Near the S 1 State
The action spectra of absorption for the deprotonated GFP chromophore near the S 1
state are shown in Fig. 5.11. The lower graph shows the spectrum for the delayed
signal of the MCP (see Fig. 5.8). The maximum of absorption (482 nm) is in good
agreement with earlier measurements at ELISA (479 nm) [29] and the recent
measurement in a quadrupole-ion trap (482.5 nm) [10].
The upper graph shows the prompt spectrum of the SED (Fig. 5.8). It is seen that
the data (prompt and delayed) have a maximum at the same wavelength (482 nm).
The prompt spectrum has major adjacent shoulders to the blue side of the main peak
at 452 nm and 422 nm and a weak one at 472 nm. Similar features were observed at
the quadrupole ion trap [10, 31] with almost the same wavelength assignments
(470, 450 and 425 nm). The identical peak position in the prompt and delayed
channels at 482 nm strongly indicates that we are addressing the same S 1 state
through two different decay channels.
It is important to note that there is a substantial contribution from a multiplephoton absorption to the main peak of the prompt spectrum. By comparing the red
side of the prompt and delayed spectra, it is realised that heating by one or two
(multiple) photons does not alter much the absorption near threshold energies for
this chromophore. This can easily be rationalised in terms of sequential resonant
absorptions. The absorption of the second photon at a given wavelength can only be
possible if the first photon is absorbed. Thus, the probability of sequential
absorptions is defined as a product of independent probabilities. If we assume
vanishing spectral overlap of individual absorptions before and after heating by
5 Photo-initiated Dynamics and Spectroscopy of the Deprotonated Green. . .
81