Reaction of Diborane with Hg 6(3P1) Atoms

Abstract

An investigation has been made of the decomposition of diborane, photosensitized by mercury-6(3P1) atoms under static conditions, at 29.30°C. The quantum yields of pressure increase and product formation have been found to be independent of substrate pressure in the complete quenching region. For runs of one hour duration at an incident light intensity of 2.5×10—6 einstein/min, the quantum yields are 0.50±0.02 for hydrogen, 0.25±0.02 for tetraborane, 0.02±0.02 pentaborane and 0.070±0.002 for pressure increase. The mean quantum yields of hydrogen and tetraborane formation were found to decrease with increasing duration of exposure during the first half-hour of irradiation. Constant values were reached after 30–45 min of exposure. The ratio of the rates of hydrogen to tetraborane formation was found to maintain a value of two, independent of substrate pressure and duration of exposure, for runs exceeding five minutes in duration. Extensive decomposition was found to lead to solid products. A mechanism is proposed involving the primary scission of the B–H bond which accounts qualitatively for the observed characteristics of the reaction. The resemblance between ethane and diborane with respect to their behavior toward Hg 6(3P1) atoms is pointed out.