Reflection-absorption infrared spectroscopy (RAIRS) of nitrous oxide (N2O) thin films is shown to provide an independent means of observing the spontelectric state, the first new structural phase of matter, with unique electrical properties, to have emerged in decades. The presence of a spontaneous and powerful static electric field within the film, the defining characteristic of spontelectric solids, is demonstrated through observations of longitudinal-transverse optical (LO-TO) splitting in RAIR spectra, using an analysis based on the vibrational Stark effect. In particular the dependence of the LO-TO splitting on the film deposition temperature may be wholly attributed to the known temperature dependence of the spontelectric field.