The C2H7O+ potential surface has been explored using the G2 procedure. Four stable structures were identified : protonated ethanol, C2H5OH2+, protonated dimethyl ether, (CH3)(2)OH+, and the electrostatic complexes C2H4 ... H ... OH2+ and CH3+... HOCH3. Experiments conducted using a selected ion flow tube identify the H3O+. C2H4 product of the ion-molecule association reaction H3O+ + C2H4 as C2H5OH2+ protonated ethanol. Rate coefficients and branching ratios are reported for reactions of the C2H7O+ ions-H3O+. C2H4 formed in the reaction of H3O+ + C2H4, C2H5OH2+, and (CH3)(2)OH+-with acrylonitrile and 2-fluorotoluene.