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Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

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4.4 Flash photolysis (FP) 82<br />

4.4 Flash photolysis (FP)<br />

• “pump-probe” technique:<br />

<strong>—</strong> generation of transient species by flash photolysis using fast flashlampor<br />

pulsed lasers (“pump”),<br />

<strong>—</strong> fast detection of transient species by UV absorption spectrometry, laser induced<br />

fluorescence (LIF), cavity ringdown spectroscopy (CRDS) (”probe”).<br />

• for gas and liquid phase reactions on nanosecond timescale (Norrish & Porter).<br />

I<br />

Figure 4.9: Typical “Pump-Probe” set-up for kinetics studies by pulsed laser photolysis<br />

and detection by laser-induced fluorescence.<br />

I<br />

Cavity Ringdown Spectroscopy (CRDS):<br />

• CRDS is an ideal method for absorption spectroscopy with pulsed lasers despite<br />

of their large (±5 %) amplitude fluctuations.<br />

• The absorption measurement is transformed into the time domain:<br />

<strong>—</strong> time dependence of signal transmitted through a resonantor:<br />

= 0 exp (−) (4.9)

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