Molecular-orbital studies of C-H bond scission induced by ionizing radiation

The correlation between the electronic structure and C-H bond scission efficiency upon exposure to ionizing radiation in relatively simple hydrocarbons has been studied by the extended Hueckel and ab initio molecular orbital methods. GF(HOMO) values, which are derived from the overlap populations of the C-H bond in the HOMO[Fsup(HOMO)(C-H) values], are found to be closely correlated with the experimental G(H2) values. This provides an expedient procedure for estimating C-H bond scission efficiency induced by ionizing radiation, without resorting to time-consuming and expensive theoretical models. Considering the reported experimental results in conjunction with the calculated results, this correlation can be explained mainly in terms of HOMO-SOMO bimolecular frontier-orbital interactions. The calculated results also indicate that C-H bond scission efficiency strongly depends upon the conformation of the C-C framework. (author)