Properties of alkali atoms in solid parahydrogen

Alkali atoms trapped in solid parahydrogen exhibit excellent spin coherence properties at high electron spin densities. We have studied potassium, rubidium, and cesium atoms implanted in parahydrogen. Different species exhibit order-of-magnitude differences in optical pumping and readout. Similarly, different alkali atoms have dramatically varying ensemble transverse relaxation times. These properties and other measurements in parahydrogen will be presented.