Orientation and alignment depolarization cross sections have been measured for the $\left(6\mathrm{}{s}^{2}6p7s\right){{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}}^{\circ }$ excited state of lead. The cross sections are characteristic of resonance collision broadening; ${\sigma }_{\mathrm{al}}=7.6\mathrm{}\times {10}^{-13\mathrm{}}$ ${\mathrm{cm}}^2$ for $v_{\mathrm{rel}}=5\mathrm{}\times {10}^4$ cm/sec. The ratio of orientation broadening to alignment broadening was found to be $\frac{{\gamma }_1}{{\gamma }_2}=1.21\mathrm{}\left(5\right)\mathrm{}$. Expressions are derived for the signal shapes in Hanle-effect, optical-double-resonance, and light-beat experiments that show which components of the signals depend on orientation and alignment relaxation times, respectively.

• Received 13 February 1967

DOI:https://doi.org/10.1103/PhysRev.160.23