The Band Spectra of Rubidium and of Its Combinations with Other Alkali Metals

The magnetic rotation spectrum of ${\mathrm{Rb}}_2$ has been observed and a vibrational analysis made. The vibrational frequency in the ${}_{}{}^1{}_{}{}^{}\Sigma$ ground state is 57.31 ${\mathrm{cm}}^{-1\mathrm{}}$ and that in the excited ${}_{}{}^1{}_{}{}^{}\Pi$ state, 48.05 ${\mathrm{cm}}^{-1\mathrm{}}$. The magnetic rotation spectrum of NaRb has also been found and has the vibrational frequencies 106.6 ${\mathrm{cm}}^{-1\mathrm{}}$ and 61.5 ${\mathrm{cm}}^{-1\mathrm{}}$ in the ${}_{}{}^1{}_{}{}^{}\Sigma$ ground and excited ${}_{}{}^1{}_{}{}^{}\Pi$ states, respectively. A band system due to RbCs has been identified.