Ab initio calculations analyze the interaction between dimethyl ether and hydroperoxy radical, and closed-shell analogues HOOH and OOH-. The two minima on each surface contain more than one H-bond. The more strongly bound structure contains a OH center dot center dot center dot O bond, along with blue-shifting CH center dot center dot center dot O; the other minimum contains exclusively CH center dot center dot center dot O. The strongest complex occurs with the anionic OOH-, followed by OOH and then HOOH. Alterations of the covalent bond lengths, vibrational frequency shifts and electronic charge shifts are associated with strengths of individual H-bonds. The data help explain how the H-bonds are affected by the open-shell character of the OOH radical. (c) 2006 Elsevier B.V. All rights reserved.