ROTATIONAL EFFECTS IN IONIC REACTIONS INVESTIGATED BY THE ZEKE-PEPICOTECHNIQUE

The acetylene ion has been investigated by the zero kinetic energy pho toelectron photoion coincidence technique (ZEKE-PEPICO). ZEKE-PES and ZEKE-PEPICO spectra recorded in the range of 500 meV above the IP reve al bending vibrations of the acetylene ion with low Franck-Condon fact ors and thus illustrate the high resolution and sensitivity of the exp eriment. The H loss reaction from acetylene ions has been investigated at different temperatures by measuring the breakdown curves in a ZEKE -PEPICO experiment. The shift between these breakdown curves has been analysed in terms of the difference in vibrational and rotational ener gy. The data show that the dissociation energy E0(T(rot)) is lowered b y 2/2 RDELTAT with increasing temperature. This result is in agreement with the simple bond fission of a molecule which is linear in the neu tral state. The dissociation energy for the H loss reaction from acety lene ions at 0 K is E0(T(rot) = 0 K) = 17.360+/-0.005 eV referenced to neutral acetylene.