The lifetime of the first excited P11 state of Mg and Ba has been obtained from the measured width of the zero-field level-crossing signal in the scattering of resonance radiation from an atomic beam of these elements. The results are τ(Mg)=(1.99±0.08)×10-9 sec and τ(Ba)=(8.2±0.2)×10-9 sec. These results are compared with previous measurements and in conjunction with other experimental results are used to obtain the intermediate coupling coefficients for the mixing of the P11 and P13 states. From a measurement of the one observable high-field level crossing in Ba137, the dipole coupling constant for the 6s6p P11 state is found to be - 113.2 ±1.0 Mc/sec in good agreement with the results of Jackson and Tuan. The quadrupole moment of the Ba137 is calculated to be 0.20×10-24 cm2 from the data of Jackson and Tuan. © 1964 The American Physical Society.