Infrared spectra are reported of complexes formed between CH4, SiH4 and GeH4 and the trans and cis isomers of nitrous acid in argon matrices. The spectra indicate that with both isomers of nitrous acid, methane forms weakly hydrogen-bonded complexes with the OH group acting as proton donor and the methane molecule as proton acceptor. The perturbation of the HONO modes in silane and germane complexes is different from that in CH4 ones and suggests that in these complexes the oxygen atom of the OH group is interacting directly with the silane or germane molecule and the major interaction in these heterodimers is an Si ... O or Ge ... O electron donor-acceptor interaction.