Measurement of the Hanle Effect for the OH Radical

We have used the coincidence of the Zn I 3072.06 {} line with the R₁₂(1) line of the (0, 0) band in the OH A²Σ⁺-X²Π ultraviolet system to perform a measurement of the molecular Hanle effect on the K^'=2, J^'=3/2 rotational level of the excited state. The OH was formed by the reaction H + NO₂ {→} OH + NO, and the Hanle linewidth is extrapolated to zero pressure of H₂ and NO₂. The half-width is found to be 258 ±{} 36 mG and the pressure broadening of the linewidth corresponds to 13 ±{} 7 mG/m Torr of NO₂ pressure and 5.2 ±{} 0.8 mG/m Torr of H₂ pressure. This linewidth gives a value of gτ=(2.20±0.27)×10^-7 sec for this excited state of the OH molecule.