NEW TECHNIQUE FOR THE MEASUREMENT OF REACTION CONSTANTS OF PHOTOCHEMICALLY PRODUCED NAH

The diffusion of NaH molecules in H-2 gas and its reactive loss mechan ism are described. The temporal behaviour of photochemically produced NaH in the reactive Na(3p)-H-2(v '' = 2,3) collision system was observ ed by means of resonant coherent anti-Stokes Raman scattering (RECARS) . A simple diffusion model, presented in this article, applies well in the lower pressure region (O mbar). The binary diffusion constant for NaH molecules in H-2, D-O = 0.7 cm(2)/s at 1 atm and 273 K, was deter mined. At higher pressures (up to 900 mbar), where the influence of di ffusion decreased, an unexpectedly rapid decay of the NaH signal is ob served. From this time behaviour we identify a new NaH loss mechanism and shown for the first time by means of time resolved CARS that this reaction can be described by a second-order rate equation in NaH.