The Rotational Analysis of theS2Bands

The emission spectrum of ${\mathrm{S}}_2$ has been obtained by means of a Geissler tube, the plates being taken in the third order of a 21 foot concave grating giving a dispersion of 0.878A per mm. The following bands have been studied; $9-1(\lambda 2857.36)$, $7-0(\lambda 2860.13)$, $8-1(\lambda 2887.84)$, $9-2(\lambda 2917.38)$ and $7-1(\lambda 2920.28)$. Each band consists of three $R$ and three $P$ branches. For small values of $K$ each band appears to have a weak and a strong $R$ branch and a weak and a strong $P$ branch. The lines of the strong branches separate into two components for $K\geqq 25$. This structure is similar to that of the Schumann-Runge bands of ${\mathrm{O}}_2$. It is concluded that the ${\mathrm{S}}_2$ bands investigated are due to a ${}_{}{}^3{}_{}{}^{}{\Sigma }_u_{}^{-}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}{\Sigma }_g_{}^{-}{}_{}{}^{}$ transition (like ${\mathrm{O}}_2$). The values of ${B_e}^{\prime \prime }$ and ${B_e}^{\prime }$ (by extrapolation) are 0.409 and 0.319 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively, the nuclear separation of the lower state being ${r_e}^{\prime \prime }=1.603\mathrm{}\times {10}^{-8\mathrm{}}$ cm and of the upper state ${r_e}^{\prime }=1.814\mathrm{}\times {10}^{-8\mathrm{}}$ cm. It is shown that the rotational levels with odd $K$ values are missing in the upper state and those with even $K$ values in the lower state. The fact that alternate levels are missing shows that the internal angular momentum of the ${\mathrm{S}}^{32}$ nucleus is zero.