Surface ionization wave discharges generated by high-voltage nanosecond pulses, propagating over a plane quartz surface and over liquid surfaces (distilled water and 1-butanol) have been studied at pressures of P=5-30 Torr. At all operating conditions, surface plasma “sheet” is diffuse and fairly uniform, both for positive and negative pulse polarities. No perturbation of the liquid surface by the discharge is detected. Both wave speed and travel distance decrease with pressure. Products of plasma chemical reaction accumulated in the ionization wave discharge over liquid butanol / saturated butanol vapor interface are detected ex situ, using FTIR absorption spectroscopy. Reaction products identified include CO, alkanes, alkynes, aldehydes, and lighter alcohols.