Rotational Structure of theΣ3→Π3Bands of BF

The rotational analysis has been made of the (0,0), (0,1), (0,2) and (1,0) bands of the $A$ system of BF. The bands are interpreted in terms of a ${}_{}{}^3{}_{}{}^{}\Sigma \to {}_{}{}^3{}_{}{}^{}\Pi$ transition with coupling intermediate between case $a$ and case $b$. The triplet separation of the upper (${}_{}{}^3{}_{}{}^{}\Sigma$) state is too small to be observed; that of the lower (${}_{}{}^3{}_{}{}^{}\Pi$) state is $-12.7\mathrm{}{B}^{\prime \prime }$. The $\Lambda$-type splitting of the ${}_{}{}^3{}_{}{}^{}\Pi$ states is less than 0.2 ${\mathrm{cm}}^{-1\mathrm{}}$. Other constants evaluated are: ${B^{\prime }}_0=1.6235\mathrm{}$, ${B^{\prime }}_1=1.6030\mathrm{}$, ${D^{\prime }}_0=-4.2\mathrm{}\times {10}^{-6\mathrm{}}$, ${D^{\prime }}_1=-9.7\mathrm{}\times {10}^{-6\mathrm{}}$, ${B^{\prime \prime }}_0=1.4030\mathrm{}$, ${B^{\prime \prime }}_1=1.3851\mathrm{}$, ${B^{\prime \prime }}_2=1.3672\mathrm{}$, all in ${\mathrm{cm}}^{-1\mathrm{}}$ units; ${I^{\prime }}_e=16.93\mathrm{}\times {10}^{-40\mathrm{}}$ g ${\mathrm{cm}}^2$, ${I^{\prime \prime }}_e=19.56\mathrm{}\times {10}^{-40\mathrm{}}$ g ${\mathrm{cm}}^2$, and ${r^{\prime \prime }}_e=1.312\mathrm{}\times {10}^{-8\mathrm{}}$ cm.