Valiev and co-workers , when attempting to probe the effects of deuteration found their methods were unable to yield results correlating positively with experiment. This was most pronounced in the case of anthracene derivatives (Table ), which should have experienced an increase in internal conversion rather than a decrease . Fischer and coworkers calculate rates of 1.6 × 10 3 s -1 and 4.4 × 10 5 s -1 for naphthalene and deuterated naphthalene in the vapour phase. It was also noted that these rates agreed well with experimental observations with respect to excess energy and deuteration.