The Structure of theαandβBand Systems of SiF

A new vibrational analysis of the $\alpha$ system of SiF is presented. The rotational structure of the (0, 0) band of this system is analyzed, giving ${B_0}^{\prime \prime }=0.5795\mathrm{}$ and ${B_0}^{\prime }=0.5743\mathrm{}$, and confirming the nature of the transition to be ${}_{}{}^2{}_{}{}^{}\Pi _{\mathrm{reg}.\mathrm{}}^{}{}_{}{}^{}\to {}_{}{}^2{}_{}{}^{}\Pi _{\mathrm{reg}.\mathrm{}}^{}{}_{}{}^{}$, with the upper state extremely near to case $b$ and the lower state near case $a$. The doublet separation in the lower state is determined, but the spin doubling in the upper state is found too small to be accurately evaluated. The $\Lambda$ type doubling is discussed. The rotational structure of the (0, 0) band of the $\beta$ system is also analyzed, and the transition confirmed to be of the type ${}_{}{}^2{}_{}{}^{}\Sigma \to {}_{}{}^2{}_{}{}^{}\Pi _{\mathrm{reg}.\mathrm{}}^{}{}_{}{}^{}$, the ${}_{}{}^2{}_{}{}^{}\Pi$ state being the lower state in the $\alpha$ system. For the ${}_{}{}^2{}_{}{}^{}\Sigma$ state $B_0=0.622\mathrm{}$ is obtained, being less accurate than the values for the other two states because of experimental difficulties encountered in photographing this band. The spin doubling in the ${}_{}{}^2{}_{}{}^{}\Sigma$ state is discussed, and the constants of the known electronic states of SiF are summarized.