Chem And Intro Flashcards
Main goal to investigate
How the TA signal is affected by
- pump beam focusing lens
- varying zntpp conc
-Laser pulse width parameters
Goal of the Tas measurement
Examine how fast the ZnTPP 3* state is depopulated after being pop by the pump laser pulse.
Immediately after pump pulse
3* highest concentration so the most probe pulse is absorbed so measure the lowest intensity and largest absorption
Over time less 3* so more light passes through so less abs
Excited state 3* decays of what time scale
Several hundred ns
Order of reaction
Ns to ms
Why can’t we measure the decay in one cycle
On order of NS or ms so data points wkhkd have to be recorded with several 100MHz to achieve sufficient resolution
Instead use shifting delay between pulses
DA of ZnTpp
Zntpp is excited and donates an electron to an acceptor and thus deactivates
Def ta
The difference in absorbance (deltaA) between two states of the system
The absorbance of the probe laser by the sample directky after the pump laser pulse and absorbance of the with probe without the pump pulse
What does ta technique study
Kinetic details of Chem processes down to ps or FS enabling detection of intermediate states of
1) photochemical reactions
2) electron transfer processes
4 processes occurring
Stimulated emission
Ground state bleaching
Excited state absorption
Photoproduct absorbtion
–++
TA signal range
+/-
Depends on which of the 4 processes dominate and is highly wavelength dependent
Here strongly positive at 450nm probe laser
Can we see the ISC
No, that is order of ps. This kit only sees like ~ns resolution
Dominating processes at 450nm probe
Excited state absorption
Photoproduct absorbtion
