Pressure effects on the vibronic transitions of NH3 and NO

Medium resolution spectra of molecules subjected to a pressure of argon indicate a broadening and a shift of Rydberg transitions, dependent on the shape of the outer orbital. Valence transitions are comparatively little affected even at 200 bar. In the case of the very complicated spectrum of NO, the washing out of the Rydberg bands allows the valence bands to show up even at a moderate pressure, so that the spectrum tends toward the spectrum of NO isolated in a solid rare gas matrix, from which spectrum discrete Rydberg bands are absent. Vibronic terms in homogeneous interaction behave, under pressure, in a way which reflects closely their degree of interaction in the free molecule.