We demonstrate a novel mechanism for hydrogen bond formation with CH group in the bimolecular complexes of adsorbed ethylene (C2H4) and oxygen (O-2) molecules on a Ag(110) surface. These complexes were created experimentally by manipulation with a scanning tunneling microscope, and characterized theoretically using ab initio density functional theory calculations. We demonstrate unambiguously that hydrogen bonding between a CH group of ethylene and O-2, whose interaction is negligible in the gas phase, has been formed in the adsorbed complexes. This unusual hydrogen bond results from adsorption induced electron transfer to the O-2, leading to enhanced electrostatic interaction between the hydrogen and oxygen, and has broad implications in biomolecular and chemical systems. (C) 2003 American Institute of Physics.