Pion-capture probabilities in organic molecules

Experimental results are presented for atomic-capture probabilities of negative pions in organic molecules. The data are analyzed in terms of atomic and molecular models. This analysis shows that the Fermi-Teller law ($Z$ law) and its modifications do not give an adequate description of the data, but that a mesomolecular model together with hydrogen transfer contains the features essential to fit the data. Clear evidence is given for chemical effects in the pion-capture process.