MODE SELECTIVITY OBSERVED IN THE DISSOCIATIONS OF EXCITED NORMAL ALKANES ALONG CARBON CARBON BONDS

Normal alkane cations from ethane to nonane are neutralized by charge-exchange reactions with cesium and sodium atoms. Surprising dissociation behavior is observed of the resulting electronically highly excited neutrals. Rapid dissociation takes place along carbon-carbon bonds, producing two radical fragments. All alkanes studied exhibit bond selectivity in their dissociation along the carbon-carbon bonds. The dissociation pathway is correlated with the parent ion geometry. The kinetic energy release spectra are measured and described by near-resonant charge transfer leading to a neutral molecule in an excited repulsive state. In the dissociation process the excess energy is distributed over rotational and translational energies of the fragments, according to the geometry of the ion at the moment of neutralization. No energy is partitioned over the fragment vibrational modes. The population of the repulsive state via the neutralization process leads to mode selective dissociations along carbon-carbon bonds in large molecules. It is suggested that predominantly triplet states are populated. These states are difficult to access directly from the electronic ground state.