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Determination of the reaction dynamics of sodium hydride in a hydrogen atmosphere with degenerate four‐wave mixing
Author(s) -
Lehr L.,
Motzkus M.,
Pichler G.,
Hering P.
Publication year - 1998
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199804)29:4<273::aid-jrs235>3.0.co;2-g
Subject(s) - chemistry , sodium hydride , hydrogen , hydride , diffusion , argon , reaction rate constant , analytical chemistry (journal) , activation energy , sodium , volume (thermodynamics) , inorganic chemistry , thermodynamics , kinetics , chromatography , organic chemistry , physics , quantum mechanics
Degenerate four‐wave mixing was successfully applied to the determination of the reactive and diffusive loss mechanisms of photochemically produced sodium hydride in Na+H 2 and Na+H 2 +Ar atmospheres and in a supplement argon filling. 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 buffer gas pressure. For small pressures (<20 hPa) diffusion out of the detection volume is the predominant process. The binary diffusion constant of sodium hydride in hydrogen was determined to be 0.66±0.07 cm 2 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 =3.8×10 ‐7 cm ‐3 s ‐1 (σ=5.6×10 ‐12 cm 2 ) at 520 K was observed. The thermal rate constant is independent of the hydrogen partial pressure, indicating that the reaction NaH+NaH→Na 2 +H 2 is most probable. The activation energy of the reaction was estimated to be of the order of 0.9 eV. © 1998 John Wiley & Sons, Ltd.