Flame spectra in the photographic infra-red

Abstract

The spectra of the flames of hydrogen, methane and carbon monoxide burning with oxygen and with nitrous oxide have been photographed in the region 6000-10,000 A. All flames in which water is a final product show a system of emission bands from the red to the far infra-red, the bands increasing in strength to longer wave-lengths. Outstanding heads have been observed at λλ6165, 6457, 6919, 7164, 8097, 8916, 9277 and 9669. It is shown that these bands are due to the vibration-rotation spectrum of H 2 O. The top of a flame of oxygen burning in hydrogen is coloured red by the emission of these bands. In the hydrogen flame the bands are probably excited mainly thermally, but the strength of these same H 2 O bands in the flame of moist carbon monoxide indicates that in this flame the excitation is a result of the combustion processes; this agrees with earlier theories on the formation of vibrationally activated molecules of CO 2 in this flame. In the hydrogen—nitrous-oxide flame new band structure in the infra-red is provisionally assigned to an extension of the ammonia α band. The methane—nitrous-oxide flame also shows the ammonia a band, and in addition strong emission of the red system of CN.