A matrix isolation IR study of laser-ablated potassium atom reactions with H-2 has been performed in solid molecular hydrogen. The KH molecule and (KH)(2) Cluster were identified by infrared spectra with isotopic substitution (HD and D-2) and by comparison to frequencies calculated using density functional theory. In para-hydrogen, the sharp KH absorption suggests dihydrogen complex formation with the ionic KH molecule, which is also characterized by an absorption at 4095 cm(-1). The highly ionic rhombic (KH)(2) molecule is formed by dimerization and trapped in solid hydrogen. Calculations at the CCSD(T) level of theory show the increasing ionic character and decreasing stability for the (MH)(2) molecule series from Li to Cs.