Knowledge Bank

The apparent complexity and the previously observed irregular isotope shift in the near-ultraviolet band spectrum of magnesium $oxide1$ gave ground for speculation that the bands may be caused by a polyatomic emitter or overlapping triplet transitions of MgO. The are spectrum of MgO in the $3750-3900\backslash AA$ region has been reinvestigated. Rotational lines of the $MgO16$ and $MgO18$ spectra have been measured from plates taken with a 21-ft. concavegrating spectrograph in the second order. It was found that the $C1\Sigma -A1\Pi$ system reported $earlier2$ extends to about $3795\backslash AA$. The bands from $3795\backslash AA$ to the longer wave lengths are members of a $D1\Delta -A1\Pi$ system and from a zero sequence. The $\Lambda -doubling$ is clearly observed in the $R\ast ,\ast$, band head region. The preliminary values of the rotational constants and vibrational frequency for the new $D1\Delta$ state are: $Bo=0.499,B1=0.494,Do=D1=1.3\times 10-6$ and $\omega e=632cm-1$.