Knowledge Bank

The absorption spectrum of $S2$ in the region 140-152 nm has been reinvestigated by taking fourth order spectra on a 6-meter normal incidence spectrograph and using `afterglow' technique with the Lyman-type flash as background source. A comparison of the present high resolution spectra (though a rotational analysis has not yet been carried out) with the earlier $studies1,2$ has revealed the following differences; (i) No doublet structure is observed except for the relatively weak bands designated as (0,0) and (1,0) of $E\leftarrow X$ and $F\leftarrow X$ systems, respectively, indicating that the bands forming doublet structure in the earlier studies may possibly belong to another system. (ii) Contrary to $E\leftarrow X$ system, the observed components of (1,0), (2,0) and (3,0) bands of the $F\leftarrow X$ system are clearly red degraded (i.e. $re\prime >re\prime \prime$, and hence weakening of bonding strength) whereas the (0,0) band does not show any clear degradation. Further, the rotational structure of the (2,0) band appears to be different from those of the (1,0) and (3,0) bands suggesting that it may not belong to the progression. (iii) No band with appreciable intensity is observed below 144 nm. In view of the above it is tentatively assumed that the states arising from the configuration\ldots $(\Pi g3p)(\Pi u5p)$ may still be approximating to Russell-Saunders coupling.