The abundance of interstellar tin and cadmium

We have determined the gas-phase interstellar abundance of the dominant ion s of tin and cadmium (Sn II and Cd II) in the diffuse clouds toward 14 and 5 stars, respectively. Our measurements show that tin is exchanged between the gas and dust phases of the diffuse interstellar medium, while cadmium i s not. The sight lines showing the highest gas-phase tin-to-hydrogen ratios (the least amount of Sn depletion) have values of Sn/H that are supersolar . Tin is the first element to show a well-determined interstellar gas-phase abundance that appears to be enriched with respect to the Sun. This findin g is direct evidence of s-process enrichment of the ISM by low- to intermed iate-mass asymptotic giant branch stars. The average Cd/H abundance ratio i n our sample is 0.09 dex below the Sun's. This ratio does not preclude an e nhancement of cadmium with respect to the Sun if Cd is incorporated into du st and/or if the adopted f-value for the cadmium transition has a large err or.