POLARIZATION OF EMISSION FROM ASYMMETRIC ROTORS .2. VECTOR REORIENTATION THROUGH INTRAMOLECULAR COUPLING AND INELASTIC-COLLISIONS

We report measurements of the linear and circular polarization ratios from fully resolved rotational levels of the asymmetric rotor NH2 popu lated by collisions with H atoms. The results compare well with a theo retical model that includes the depolarizing effects of intramolecular coupling of rotational angular momentum N to nuclear and to electron spin. These have a very significant influence on fluorescence polariza tion. The model also incorporates the tilting of the N vector in the m olecule frame that occurs when inter-k stack transitions take place. C hanges in N vector orientation are described with the aid of the angul ar momentum sphere, a classical representation of the motion of the N vector in a molecule fixed frame. The theoretical treatment assumes th e classically impulsive limit for the collisional interaction with con servation of the m quantum number along the kinematic apse. This descr iption of the fate of the N vector under the influence of intra- and i ntermolecular interactions allows stereodynamical conclusions to be dr awn from experimental observations of fluorescence polarization. (C) 1 997 American Institute of Physics.