Resonances in rotationally inelastic scattering of OH($X^2Pi$) with helium and neon

We present detailed calculations on resonances in rotationally and spin-orbit inelastic scattering of OH ($X,^2Pi, j=3/2, F_1, f$) radicals with He and Ne atoms. We calculate new emph{ab initio} potential energy surfaces for OH-He, and the cross sections derived from these surfaces compare favorably with the recent crossed beam scattering experiment of Kirste emph{et al.} [Phys. Rev. A textbf{82}, 042717 (2010)]. We identify both shape and Feshbach resonances in the integral and differential state-to-state scattering cross sections, and we discuss the prospects for experimentally observing scattering resonances using Stark decelerated beams of OH radicals.

Scattering resonances in slow NH${}_3$-He collisions

We theoretically study slow collisions of NH$_3$ molecules with He atoms, where we focus in particular on the observation of scattering resonances. We calculate state-to-state integral and differential cross sections for collision energies ranging from 10${}^{-4}$ cm$^{-1}$ to 130 cm$^{-1}$, using fully converged quantum close-coupling calculations. To describe the interaction between the NH${}_3$ molecules and the He atoms, we present a four-dimensional potential energy surface, based on an accurate fit of 4180 {it ab initio} points. Prior to collision, we consider the ammonia molecules to be in their antisymmetric umbrella state with angular momentum $j=1$ and projection $k=1$, which is a suitable state for Stark deceleration. We find pronounced shape and Feshbach resonances, especially for inelastic collisions into the symmetric umbrella state with $j=k=1$. We analyze the observed resonant structures in detail by looking at scattering wavefunctions, phase shifts, and lifetimes. Finally, we discuss the prospects for observing the predicted scattering resonances in future crossed molecular beam experiments with a Stark-decelerated NH$_3$ beam.

Scattering of Stark-decelerated OH radicals with rare-gas atoms

We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH ($X,^2Pi_{3/2}, J=3/2, f$) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D$_2$ as a function of the collision energy between $sim 70$ cm$^{-1}$ and 400~cm$^{-1}$. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on accurate emph{ab initio} potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [Gilijamse emph{et al.}, Science {bf 313}, 1617 (2006)], Ar [Scharfenberg emph{et al.}, Phys. Chem. Chem. Phys. {bf 12}, 10660 (2010)], He, and D$_2$ [Kirste emph{et al.}, Phys. Rev. A {bf 82}, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.