H-D isotope effects in the decomposition of acetylene by electron impact

In an attempt to gain a better insight into the decomposition of small polyatomic molecules by irradiation, H-D isotope effects in the mass spectrum of acetylene are predicted by means of the quasi-equilibrium theory of mass spectra, and are compared with observed effects. The qualitative agreement between calculated and experimental isotope effects for fragment ions is good, and the quantitative agreement is fair in view of the uncertainty in several quantities, especially in the excitation energy distribution for molecular ions. It is concluded that the quasi-equilibrium theory provides a satisfactory account of the main phenomena which determine the decomposition pattern. There are however several indications that excitation energy is not completely randomly distributed in ions, and this might have to be taken into account in more refined treatments.