Determination of the reaction dynamics of sodium hydride in a hydrogen atmosphere with degenerate four-wave mixing
✍ Scribed by L. Lehr; M. Motzkus; G. Pichler; P. Hering
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 358 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0377-0486
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✦ Synopsis
Degenerate four-wave mixing was successfully applied to the determination of the reactive and di †usive loss mechanisms of photochemically produced sodium hydride in and atmospheres and in a Na + H 2 Na + H 2 + Ar supplement argon Ðlling. Sodium hydride is formed on the microsecond time-scale in a quenching-reaction sequence after the 3s-3p excitation of sodium in the excitation volume. The concentration of NaH decreases with time depending on the bu †er gas pressure. For small pressures (AE20 hPa) di †usion out of the detection volume is the predominant process. The binary di †usion constant of sodium hydride in hydrogen was determined to be 0.66 » 0.07 cm2 s-1 at 1013 hPa and 273 K. Moreover, experimental data show an additional reactive loss mechanism present at high gas pressures. A second-order reaction with a thermal rate constant of k 2 = 3.8 Â 10-7 cm-3 s-1 (r = 5.6 Â 10-12 cm2) at 520 K was observed. The thermal rate constant is independent of the hydrogen partial pressure, indicating that the reaction is most probable. The activation energy of NaH + NaH Ç Na 2 + H 2 the reaction was estimated to be of the order of 0.9 eV.