Influence of Rotational Relaxation on Tropospheric O H Laser Induced Fluorescence Measurements

Rotational relaxation of OH molecules in the -II electronic ground state has been observed to occur in collisions with water molecules with gas kinetic probability. It causes an additional contribution to the already well known sources of interference when LIF is used to monitor tropospheric OH. As the laser generated OH is originally produced mostly in high rotational states, the fast relaxation phenomenon leads to a further population of OH in low rotational states. These states are used to monitor tropospheric OH by spectroscopic methods. The observed effect therefore increases the interference. A mathematical analysis is presented, revealing the effect of all relevant parameters.