Molecular beam scattering of NO + Ne: A joint theoretical and
experimental study
Y. Kim and H. Meyer
Department of Physics and Astronomy, The University of Georgia, Athens, Georgia
30602-2451
M. H. Alexander
Department of Chemistry and Biochemistry, The University of Maryland, College
Park, Maryland 20742-2021
The collision dynamics of the NO + Ne system is investigated in a molecular beam
scattering experiment at a collision energy of 1055 cm–1. Employing resonance
enhanced multiphoton ionization of NO, we measured state-resolved integral and
differential cross sections for the excitation to various levels of both
spin-orbit manifolds. The dependence of the scattered intensity on the laser
polarization is used to extract differential quadrupole moments for the
collision induced angular momentum alignment. The set of cross section data is
compared with results of a full quantum mechanical close coupling calculation
using the set of ab initio potential energy surfaces of Alexander et al. [J.
Chem. Phys. 114, 5588 (2001)]. In previous work, it was found that the positions
and rotational substructures for the lowest bend-stretch vibrational states
derived from these surfaces agree very well with the observed spectrum of the
NO–Ne complex. For the same potential, we find that the calculated cross
sections show a less satisfactory agreement with the experimental data. While
the overall Jf dependence and magnitude of the integral and differential cross
sections are in good agreement, noticeable discrepancies exist for the angle
dependence of the differential cross sections. In general, the calculated
rotational rainbow structures are shifted towards larger scattering angles
indicating that the anisotropy of the potential is overestimated in the fit to
the ab initio points or in the ab initio calculation itself. For most states, we
find the measured alignment moments to be in excellent agreement with the
results of the calculation as well as with predictions of sudden models.
Significant deviations from the sudden models are observed only for those
fine-structure changing collisions which are dominated by forward scattering.
Results of the full quantum calculation confirm the deviations for these states.