The Carbon Monoxide Flame Bands

R. N. Dixon


The carbon monoxide flame bands have been photographed under high resolution from an afterglow source. Bands in the wavelength range 3100 to 3800 $\overset{\circ}{\mathrm A}$ show a pattern which has been reproduced by calculations of the energies of high vibrational levels of the $^1\sum^+_g$ ground state of CO$_2$. The structure of this energy level pattern is strongly affected by extensive Fermi resonance in the $^1\sum^+_g$ state. The spectrum is emitted by excited CO$_2$ molecules which radiate to the ground state from the lowest vibrational level and from the $v'_z$ = 1 level of a B$_2$ state. This excited state lies approximately 46 000 cm$^{-1}$ above the lowest level of the ground state, and has an OCO angle of 122 $\pm$ 2$^\circ$ and a CO bond length of 1.246 $\pm$ 0.008 $\overset{\circ}{\mathrm A}$. Combination of these results with the work of other authors shows that the excited state is a $^1$B$_2$ state, and that the carbon monoxide flame bands are associated with the weak absorption system of CO$_2$ at 1475 $\overset{\circ}{\mathrm A}$.