Weakly bonded complexes of water with oxygen and nitrogen are studied using ab initio methods; their thermodynamic functions and infrared spectra are calculated. Infrared spectra for these complexes exhibit several interaction-induced low-frequency modes, while their estimated atmospheric fractions appear to be larger than for many recognized "greenhouse" species. This implies that atmospheric H2O-O-2 and H2O-N-2 complexes may absorb more of the earth＇s surface radiation than individual molecules and thus contribute to a "greenhouse" effect.