Pulsed Laser Photolysis (PLP)
This technique allows the production of radicals from UV photolysis of a suitable precursor using a KrF excimer laser (248 nm). The formation of radicals takes place along the gas jet. The photolysis laser crosses the reservoir, the Laval nozzle and the rotary disk inside the CRESU chamber.
H2O2 + hν248nm → 2OH(X2∏)
Internal view of the reservoiro: 1. Entrance of lasers; 2. Gas flow inlets and connections to pressure transducers; 3. Flexible shaft that makes the rotary disk rotate.
Laser-Induced Fluorescence (LIF)
The laser induced fluorescence technique consists in exciting the radicals formed by PLP to an electronic upper state and then the spontaneous light emission is monitored as a function of reaction time.
Excitation transition: OH(X2∏, v’’=0) + hνexcit(λ ~ 282 nm) ” OH(A2Σ+, v’=1)
LIF transition: OH(A2Σ+, v’=0) → OH(X2∏, v’’=0) + hνLIF(λ ~ 309 nm)
The emitted light is focused by an optical system on a fast response photomultiplier. This transforms the light signal in an electrical signal (ILIF(t)), which depends on the reaction time as:
ILIF(t) = ILIF (t=0) exp (-k′t)
Photograph of the optical system inside the CRESU chamber: 1. Optical filter; 2. Plano-convex lenses; 3. High-reflectance mirror. 4. Gas inlet to the reservoir.
Detection system of LIF: 1. Optical system; 2. Photomultiplier tube (PMT); 3. PMT power supply.