2179.     MARSHALL, A. L.  Synthetic Formaldehyde From Carbon Monoxide and Hydrogen.  Mechanism of the Sensitized Photochemical Reaction.  Jour. Phys. Chem., vol. 30, 1926, pp. 1634-1640; Chem. Abs., vol. 21, 1927, p. 534.

        Kinetic study is continued of the photochemical reaction between H₂ and CO when sensitized by Hg vapor to light of wavelength 2536.7 Å. U. from a H₂O-cooled Hg arc.  The gases were saturated with Hg at 50°, and the reaction chamber was maintained at 80°.  The apparatus and method were the same as those previously described.  Measurements were made of the amount of energy absorbed while the reaction was proceeding.  The data for the last of a series of 10 experiments were:  Volume of apparatus, 890 cc.; initial gas mixture, 510 mm. CO, 279 mm. H₂; absorption rate, 1.35 (10)¹⁹ quanta per min.; maximum rate of reaction 2.1 mm. per min. corresponding to 3.3 (10)¹⁹ molecules of HCHO formed, or quantum yield of 2.44.  The reaction product formed was largely HCHO or a polymer. In 1 experiment, 138 cc. of a theoretical 200 cc.³ of HCHO were recovered.  A study of the velocity constants calculated by various possible kinetic equations makes it apparent that the velocity depends in some way on the ½ power of the H₂ and the 1^st power of the CO concentration.  This would seem to mean that the velocity depends on the concentration of atomic H.  The most satisfactory equation expressing the velocity is d/dt(HCHO)=k(√P_H2)(P_CO).  The reaction between CO₂ and H₂ was reinvestigated, and it was found that reaction proceeds at a relatively slow rate.