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Comparison of the Na(4p) + H2 and Na(3p) + H2 reactive/quenching systems studied with CARS, resonance-enhanced CARS and DFWM

Three different non-linear optical techniques, CARS (coherent anti-Stokes Raman scattering), Resonance enhanced CARS and DFWM (degenerate Four-Wave-Mixing), have been used to compare the reactive and quenching behavior of different electronic excited sodium atoms, Na(3p) and Na(4p), in a collision with H2.In the chemical reaction channel both excited sodium states produce NaH-molecules, but in the case of Na(3p) we show that the reaction is not a direct formation process and involves more than one step. Both sodium states induce a population of the vibrational levels v"=0-3. For the 3p-excitation the maximum of the NaH population distribution is concentrated at v"=0 while the excitation of the Na(4p) state NaH results in a maximum population of the v"=1 level. The differences are attributed to different potential surfaces. For the quenching investigations we focused the studies on the behavior of the Na(4p) state and compared the results with the well-known behavior of the Na(3p) state. Because no quenching products have been detected in the CARS spectra, the integrated quenching cross section has been estimated to be less than 5(10-17 cm2 based on the detection sensitivity of the CARS apparatus.

reactive/quenching systems; resonance-enhanced CARS; DFWM

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