The interaction between the peroxy radical and water, hydrogen chloride, chlorine, and ammonia has been studied in argon matrixes. The peroxy radical acts as a hydrogen bond donor toward ammonia and forms a strong hydrogen bond to the ammonia nitrogen, significantly stronger than the corresponding water ammonia bond. Hydrogen chloride binds to the lone pair of the terminal oxygen of the peroxy radical, which in this case is a hydrogen bond acceptor. The complex shift of the hydrogen chloride stretch indicates a slightly weaker hydrogen bond than in the hydrogen chloride-water complex. The shift of the OH stretch of the complexed peroxy radical suggests the presence of a weak hydrogen bond from the peroxy radical hydrogen to one of the lone pairs of the chlorine atom of HCl. Water forms a cyclic complex with the peroxy radical, with both molecules donating and accepting hydrogen bonds. Both one water OH stretch and the OH stretch of the peroxy radical are strongly shifted in the complex. The results of this study suggest that the peroxy radical is a significantly stronger acid than water and that it readily accepts hydrogen bonds.