THE DETERMINATION OF TRANSITION-STATE PROPERTIES IN THE ETHANE AND ETHENE ION DISSOCIATION

The dissociation of ethane and ethene ions has been investigated by me ans of the ZEKE-PEPICO technique. The breakdown curves for the lowest reaction channel - in both molecular ions the H-2 loss reaction - has been measured at temperatures of 300 K and close to 0 Kelvin. The obse rved shift of the breakdown curves at the two temperatures is 12 meV i n the case of ethane ions and 8 meV in the case of ethene ions. These numbers can essentially be explained by the difference in the vibratio nal energy at the two temperatures. In both cases it is concluded that the dissociation energy E(0)(J) does not depend significantly on the rotational angular momentum of the molecules which is expected for rea ctions governed by a tight transition state. These findings are discus sed in terms of the energetic, kinetic, and mechanistic information av ailable for these reactions.