Rotational and Vibrational Structure of the Fourth Positive Bands of Carbon Monoxide

The rotational structure of twelve of the fourth positive bands of CO ($A{}_{}{}^1{}_{}{}^{}\Pi -X{}_{}{}^1{}_{}{}^{}\Sigma$) has been measured and analyzed. The analyses of two bands are given. The values obtained for the rotational constants of the normal state are $B_0=1.9170\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\alpha =0.01738\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. This is in disagreement with the result of infrared band measurements, which give $B_0=1.84\mathrm{}$. The data obtained on the excited $A{}_{}{}^1{}_{}{}^{}\Pi$ state are in complete agreement with the results of Angstrom ($B{}_{}{}^1{}_{}{}^{}\Sigma -A{}_{}{}^1{}_{}{}^{}\Pi$) band studies. The higher value of $B_0$ for the normal state is verified by measurement of the 0-0 band of the ultraviolet system $B{}_{}{}^1{}_{}{}^{}\Sigma -X{}_{}{}^1{}_{}{}^{}\Sigma$. The recently reported predissociation of the $B$ state is also observed in this band. New measurements are given of the fourth positive band heads below 2270A. A formula is given to represent all the known band heads, and from this a formula for band origins is obtained.