POLARIZATION OF EMISSION IN ASYMMETRIC ROTORS .1. THE EFFECTS OF ELASTIC COLLISIONS, ELECTRON AND NUCLEAR SPINS

We report measurements of the linear and circular polarization ratios as a function of rotational state for the asymmetric rotor NH2. This m olecule displays fine structure splitting from its unpaired electron a nd hyperfine structure from coupling with the nuclear spins. We presen t a theory of polarized emission for this molecule which includes the effects of fine and hyperfine interactions. These have a marked effect on the polarization ratios and are well described by a theory in whic h the effect of electron and nuclear spin are introduced as time-indep endent perturbation coefficients. We find that theory predicts differe nt values of polarization ratio according to the manner of coupling of the proton nuclear spins. The best fits to experimental data are obta ined when the coupling follows a physically intuitive scheme rather th an that usually. adopted. When all intramolecular couplings due to ele ctron and nuclear spins are properly accounted for; there is no depola rization that may be attributed to the effect of elastic collisions. T hus, as in the case of diatomic molecules, orientation and alignment s how a marked stability to change by collision. (C) 1997 American Insti tute of Physics.