in gaseous matrix byproducts: HfH4; other Radiation; laser-ablated Hf atoms were reacted with H2 and O2 molecules in excess argon full-arc irradiation and annealin to 24-30 K; Andrews, L. Chem. Soc. Rev., 2004, 33, 123; detected by IR spectra;

in neat (no solvent) (further products), laser ablated Hf co-deposited with H2+O2 in excess Ar onto a 10K CsI window, annealed at 24-30 K (mechanism discussed); not isolated, detected by IR;