The rotational transitions for which $J=0\mathrm{}\to 1$ were studied by the molecular beam electric resonance method for the first three vibrational states, $v=0, 1, 2$, of ${\mathrm{Rb}}^{85}$${\mathrm{Cl}}^{35}$ and the ground vibrational state, $v=0\mathrm{}$, of ${\mathrm{Rb}}^{87}$${\mathrm{Cl}}^{35}$. The molecular constants are: The quadrupole ($\mathrm{eqQ}$) and spin-rotation ($c$) interaction constants of ${\mathrm{Rb}}^{85}$${\mathrm{Cl}}^{35}$ are: For the $v=0\mathrm{}$ state of ${\mathrm{Rb}}^{87}$${\mathrm{Cl}}^{35}$, ${\mathrm{}\left(\mathrm{eqQ}\right)\mathrm{}}_{\mathrm{Rb}}=-25.485\mathrm{}\pm 0.006$ Mc/sec. The ratio of the Rb quadrupole moments is $\frac{Q_{85}}{Q_{87}}=2.0669\mathrm{}\pm 0.0005$. The mass ratio of the Rb isotopes is $\frac{M_{85}}{M_{87}}=0.9770163\mathrm{}\pm 0.0000045$.

• Received 2 August 1954

DOI:https://doi.org/10.1103/PhysRev.96.968