timescale of picoseconds, so that anything that happens after has a statistical nature.
The reason behind that is a very high vibrational level density of the anion in the S 0
state after ‘heating’ by one-photon absorption. The hot ground state may then
proceed and decay by Arrhenius-type statistical fragmentation (SF) or by thermionic electron emission (Tem), a delayed vibrationally mediated electron ejection
process [39, 40], with a relative strength that depends on the respective activation
energies [41]. The Beyer-Swinehart algorithm together with calculated vibrational
frequencies of the deprotonated GFP chromophore were used to calculate the
vibrational level density of the anion in the S 0 state as a function of excitation
energy. The density is indeed very high (~10
27
/cm
À1 ) at the excitation energy of
2.9 eV, corresponding to excitation at 480 nm plus 0.3 eV internal energy at room
temperature (Fig. 5.5), thus creating a vibrational quasi-continuum at this energy.
We have identified negatively charged dissociation products, which by itself
does not exclude the co-existence of the emission of an electron from the hot ground
state. From the opening of the prompt channel at about 500 nm, one can judge that
the electron affinity is about 2.5 eV. As will be discussed later, the experimental
vertical detachment energy is 2.68 eV [35] and is located very close to the adiabatic
T(K)
C
v (meV/K)
E(eV)
0
100
200
300
0
0.2
0.4
T(K)
Fig. 5.5 Internal energy and
heat capacity as a function of
temperature, calculated based
on the vibrational frequencies
of the GFP chromophore
anion. The inset shows the
internal energy as a function
of the temperature below
room temperature
5 Photo-initiated Dynamics and Spectroscopy of the Deprotonated Green. . .
75
The reason behind that is a very high vibrational level density of the anion in the S 0
state after ‘heating’ by one-photon absorption. The hot ground state may then
proceed and decay by Arrhenius-type statistical fragmentation (SF) or by thermionic electron emission (Tem), a delayed vibrationally mediated electron ejection
process [39, 40], with a relative strength that depends on the respective activation
energies [41]. The Beyer-Swinehart algorithm together with calculated vibrational
frequencies of the deprotonated GFP chromophore were used to calculate the
vibrational level density of the anion in the S 0 state as a function of excitation
energy. The density is indeed very high (~10
27
/cm
À1 ) at the excitation energy of
2.9 eV, corresponding to excitation at 480 nm plus 0.3 eV internal energy at room
temperature (Fig. 5.5), thus creating a vibrational quasi-continuum at this energy.
We have identified negatively charged dissociation products, which by itself
does not exclude the co-existence of the emission of an electron from the hot ground
state. From the opening of the prompt channel at about 500 nm, one can judge that
the electron affinity is about 2.5 eV. As will be discussed later, the experimental
vertical detachment energy is 2.68 eV [35] and is located very close to the adiabatic
T(K)
C
v (meV/K)
E(eV)
0
100
200
300
0
0.2
0.4
T(K)
Fig. 5.5 Internal energy and
heat capacity as a function of
temperature, calculated based
on the vibrational frequencies
of the GFP chromophore
anion. The inset shows the
internal energy as a function
of the temperature below
room temperature
5 Photo-initiated Dynamics and Spectroscopy of the Deprotonated Green. . .
75