Alignment Effects in the Fully Quantum State Resolved Inelastic NO(X) + Rare Gas Collisions

The rotational alignment effects in the rotationally inelastic scattering of NO(X$^{2}\Pi _{1/2})$ with Ar and Kr have been investigated by means of quantum mechanical, quasi-classical trajectory, and Monte Carlo scattering calculations. It has been shown that the repulsive nature of the interaction potential at a collision energy of 65meV is primarily responsible for the rotational alignment. On the other hand, the alternating trend in the integrated quantum mechanical parity resolved alignment moments as a function of the final rotational state reflects differences in the differential cross sections for the total NO(X) parity conserving and changing collisions due to quantum interferences, rather than a difference in stereodynamics. Ion-images for NO(X) resolved in \textit{$\Lambda $}-doublet levels were collected with a hexapole state selective cross molecular beam ion-imaging apparatus using linearly polarised light. Scattering angle resolved rotational alignment moments were retrieved from the images using a newly developed data analysis algorithm. The agreement is excellent between the experimental and the quantum data. To the best of our knowledge this is the first instance when experimental \textit{$\Lambda $}-doublet resolved alignment moments are reported.