Alkali reactions with wall coating materials used in atomic resonance cells

It is well known that the chemisorption of various chlorosilane materials on glass atomic storage vessel walls results in surface coatings which inhibit electronic- and nuclear-spin relaxation. In the present study the chemical reaction of rubidium, and by analogy other alkali metals, with dichlorodimethylsilane-treated glass surfaces has been studied. We find evidence that rubidium reacts with a freshly prepared coating to produce H2 and a volatile silicon-containing species. The most reasonable reaction process is postulated to be rubidium reacting with residual silanol groups (Si-OH) found on the surface. As the reaction proceeds these groups would disappear, thus reducing the spin-relaxation rate associated with the surface. We believe that this reaction results in the ‘‘curing’’ of wall coatings reported by other investigators. Concurrently, the gaseous reaction products become impurities within the system. The spin-relaxation cross section of the silicon-containing species is expected to be less than 1×10−17 cm2.