Intensity Anomalies and Perturbations in the CN Bands

Abstract

The rotational structures of the 0,0 violet and the 9,4 red CN bands, developed by CH${\mathrm{Cl}}_{3}$ in active nitrogen, are measured on plates from the first and second orders of a 30-ft. grating. The rotational constants of the ${b}^{2}\ensuremath{\Sigma},v=0$ and the ${a}^{2}\ensuremath{\Sigma},v=4$ states are in good agreement with the previously published values; those for the $v={9}^{2}\ensuremath{\Pi}$ state are $B_{}^{\ensuremath{'}}{}_{9}{}^{}=1.5312\ifmmode\pm\else\textpm\fi{}0.0008$ ${\mathrm{cm}}^{\ensuremath{-}1}$, $D_{}^{\ensuremath{'}}{}_{9}{}^{}=7.408\ifmmode\pm\else\textpm\fi{}0.002\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The A-doubling in this state, except for four perturbations, can be represented by use of the constants ${p}_{0}=+0.01597$ and ${q}_{0}=\ensuremath{-}0.00080$. The value ${\ensuremath{\gamma}}^{\ensuremath{'}}=+0.021$ is determined for the spin doubling in the ${b}^{2}\ensuremath{\Sigma},v=0$ state. Four perturbations are found at $K=4,7,11, \mathrm{and} 15$ for ${b}^{2}\ensuremath{\Sigma}$; extra $P$ and $R$ lines separated from the main lines by $\ensuremath{\Delta}\ensuremath{\nu}=\ensuremath{-}0.352 {\mathrm{cm}}^{\ensuremath{-}1},+0.938 {\mathrm{cm}}^{\ensuremath{-}1},+1.177 {\mathrm{cm}}^{\ensuremath{-}1}, \mathrm{and} +1.212$ ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, appear in both the 0,0 and 0,1 bands of the violet system. In the red system, shifts of the right amount and direction in the lines ${Q}_{1}[3\frac{1}{2}]$, ${R}_{1}[7\frac{1}{2}]$, ${P}_{1}[7\frac{1}{2}]$, ${R}_{2}[10\frac{1}{2}]$, ${P}_{2}[10\frac{1}{2}]$, and ${Q}_{2}[15\frac{1}{2}]$ confirm the assumption that rotational levels of $^{2}\ensuremath{\Pi},v=9$, perturb those of ${b}^{2}\ensuremath{\Sigma},v=0$, and that the perturbations occur for the $K$ and $J$ values indicated. (Brackets denote upper state $J$.) The values of the perturbation matrix elements are obtained for the various levels. Some anomalies of the $R$ branch band lines in the range 23-29 of ${K}^{\ensuremath{'}}$ values in the 0,0 violet band are mentioned.The mechanism responsible for the enhancements of the main and extra lines of the 0,0 violet band is discussed. Collisions involving interstate transfer ($^{2}\ensuremath{\Pi}\ensuremath{\rightarrow}{a}^{2}\ensuremath{\Sigma}$) evidently occur, or are enhanced, at each perturbed level; and rapid redistribution of molecules among rotational levels by collisions must also occur. Where spin doublets are resolvable in the violet bands, rotational redistribution occurs without change of spin direction.