Summary: Polarization of emission in asymmetric rotors. I. The effects of elastic
collisions, electron and nuclear spins
Kaspars Truhins, Zeyad T. Al Wahabi, Marcis Auzinsh,a)
Anthony J. McCaffery,
and Zaid Rawi
School of Molecular Sciences, University of Sussex, Brighton BN1 9QJ, United Kingdom
Received 24 October 1996; accepted 25 November 1996
We report measurements of the linear and circular polarization ratios as a function of rotational state
for the asymmetric rotor NH2. This molecule displays fine structure splitting from its unpaired
electron and hyperfine structure from coupling with the nuclear spins. We present 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 which
the effect of electron and nuclear spin are introduced as time-independent perturbation coefficients.
We find that theory predicts different values of polarization ratio according to the manner of
coupling of the proton nuclear spins. The best fits to experimental data are obtained when the
coupling follows a physically intuitive scheme rather than that usually adopted. When all
intramolecular couplings due to electron and nuclear spins are properly accounted for; there is no
depolarization that may be attributed to the effect of elastic collisions. Thus, as in the case of
diatomic molecules, orientation and alignment show a marked stability to change by collision.
© 1997 American Institute of Physics. S0021-9606 97 00509-6