Methanol, ethanol, or 1-propanol was introduced into vacuum as a continuous liquid flow (liquid beam) and was subjected to nonresonant multiphoton ionization under irradiation of a 270 nm laser. Ions ejected into vacuum were mass-analyzed by means of time-of-flight mass spectrometry, where the ions were extracted by a static electric field, or a pulsed electric field with a delay time of similar to 1.6 mu s with respect to a pulse laser. Ions, H+(ROH)(n) (n greater than or equal to 1), were dominantly produced by ion-molecule reactions in the liquid beam. On the other hand, H+(CH3)(2)O was interpreted to be produced by unimolecular dissociation of H+(CH3OH)(2) in the gas phase, and its rate constant was estimated to be (5 +/- 3) x 10(4) s(-1). This small rate constant suggests that the internal energy of the H+(CH3OH)(2) is dissipated efficiently into the liquid, so that the rate constant is much smaller than that for the same process in H+(CH3OH)(2) produced by ionization of a gas phase cluster. In addition, the fragment ions, H+ and C+, having similar kinetic energies of similar to 8 eV are considered to be produced by a multiphoton process.