Ultraviolet-induced isotope exchanges in gaseous mixtures of HCl and D2 and of DCl and H2

Mixtures of HCl and D2 and of DCl and H2 were irradiated with an ultraviolet mercury resonance lamp and analyzed mass spectrometrically for the different isotopic species of hydrogen. It was found that at room temperature the reaction H+DCl–>HD+Cl is slower than the exchange reaction H+DCl–>D+HCl. This is to be expected from a consideration of activation energies, but it is in apparent contradiction to earlier results obtained by Leighton and Cross and by Steiner and Rideal. The reaction between hydrogen atoms and hydrogen molecules was found to be much faster at this temperature than is usually estimated.