Assuming that ∆ f H Pt(111) is zero (a common assumption that we will discuss later), ∆ f H CH * 4 can be calculated directly with ∆ f H CH 4 from the ATcT database in the thermochemical cycle in Fig. . Temperature corrections have to be applied to convert between the experimental and the reference temperature. How- ever, many species dissociate easily once adsorbed or do not have a stable gas-phase precursor, requiring specialized precursors to measure their adsorption energy. For example, Karp and coworkers 120,121 used CH 3 I as a precursor to determine ∆ f H* CH 3