Calorimetric Measurement of the Heat of Adsorption of Benzene on Pt(111)†

The heat of adsorption of benzene on clean Pt(111) at 300 K is measured calorimetrically and found to decrease with coverage (ı) as (197- 48ı- 83ı2) kJ/mol. Saturation coverage (ı) 1.0) is 2.3 1014 molecules/cm2. Sticking probabilities of benzene on Pt(111) were measured by mass spectrometry, giving an initial value of 0.97 and showing Kisliuk-type behavior with increasing coverage that implies there is a precursor to sticking with a ratio of its hopping rate to its desorption rate of 28. Benzene adsorbs transiently on the benzene-saturated surface at 300 K with a trapping probability of 0.90 and a heat of adsorption of 63-73 kJ/mol. 1