The reactions of group V metal dioxide molecules with dihydrogen have been studied by matrix isolation infrared spectroscopy. The ground state VO2 molecule is able to cleave dihydrogen heterolytically and spontaneously in forming the HVO(OH) molecule in solid argon. In contrast, the reaction of VO2 with dideuterium to form DVO(OD) proceeds only under UV-visible excitation via a weakly bound VO2(eta(2)-D-2) complex. Theoretical calculations predict that the dihydrogen cleavage process is thermodynamically exothermic with a small barrier. The niobium and tantalum dioxide molecules react with dihydrogen to give primarily the side-on bonded metal dioxide bis-dihydrogen complexes, NbO2(eta(2)-H-2)(2) and TaO2(eta(2)-H-2)(2), which are further transferred to the HNbO(OH) and HTaO(OH) molecules via photoisomerization in combination with H-2 elimination under UV-visible light excitation.