Reactive ion scattering spectrometry (RISS) utilizing low-energy (<100 eV) ion-surface collisions was characterized by using model systems composed of mixed methyl- and hydroxy-terminated self-assembled monolayers (SAMs). Mixed monolayers were prepared by immersing a gold substrate in mixed solutions of dodecanethiol (CH3(CH2)(11)SH; C12- or CH3-terminated surface) and 1-hydroxyundecanethiol (HO(CH2)(11)SH; C11OH- or OH-terminated surface) in tetrahydrofuran or in ethanolic solutions of the unsymmetrical disulfide (CH3(CH2)(11)SS(CH2)(11)OH) for 24 h. The film created from the unsymmetrical disulfide (approximately 50% CH3 and 50% OH terminating) was used for comparison with the 50:50 film prepared from the mixture of the two corresponding thiols. In a tandem quadrupole instrument, the first quadrupole mass selects ions to collide with the mixed monolayers, and then product ions from the collision are analyzed with the second quadrupole. Benzene molecular ions undergo translational to internal energy conversion (fragmentation), electron transfer (neutralization), and atom/group transfers (ion-surface reactions) upon collision with SAMs. Fragmentation and neutralization observed for benzene molecular ion increase with an increase in the percentage of OH groups present on the surface. The incremental change detected in the relative fragmentation with change in percent composition suggests that H-bonding expected at high %OH does not increase the translational to internal energy conversion detected for the projectile ion at the energies used here; no large "step" change in energy deposition is detected as the %OH is decreased to values that would prevent H-bonding. Benzene molecular ion, C6H6.+ (m/z 78), can react with methyl groups to form the reaction product, C7H7+ (m/z 91), and its corresponding fragment ion, C5H5+ (m/z 65). The methyl abstraction ion-surface reaction product ions can be correlated to the relative concentrations of CH3 groups in mixed methyl- and hydroxy-terminated SAMs.