State-to-state inelastic scattering of Stark-decelerated OH radicals with Ar atoms

Abstract

The Stark deceleration method exploits the concepts of charged particle accelerator physics to produce molecular beams with a tunable velocity. These tamed molecular beams offer interesting perspectives for precise crossed beam scattering studies as a function of the collision energy. The method has advanced sufficiently to compete with state-of-the-art beam methods that are used for scattering studies throughout. This is demonstrated here for the scattering of OH radicals (X 2 P 3/2 , J = 3/2, f) with Ar atoms, a benchmark system for the scattering of open-shell molecules with atoms. Parity-resolved integral state-to-state inelastic scattering cross sections are measured at collision energies between 80 and 800 cm À1 . The threshold behavior and collision energy dependence of 13 inelastic scattering channels is accurately determined. Excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on the most accurate ab initio OH + Ar potential energy surfaces to date.

Resonances in rotationally inelastic scattering of OH(X2Π) with helium and neon

“…This level, which is the higher Λ-doublet component of the ground rotational level (see Fig. 1), can be selected with the Stark decelerator since it is low-field seeking in an inhomogeneous electric field [13]. The cross sections are computed on a very fine grid of energies to be able to study resonant features in detail.…”

“…The recently developed Stark deceleration technique, taking advantage of the interaction of polar molecules with timevarying electric fields, has allowed continuous tuning of the beam velocity [12]. This has facilitated measurements of the collision energy dependence of state-to-state integral cross sections down to energies of 70 cm −1 [13]. Moreover, the velocity spread in such decelerated beams is much smaller than in conventional molecular beams.…”

“…Moreover, the velocity spread in such decelerated beams is much smaller than in conventional molecular beams. Thus far, an energy resolution of ≥ 13 cm −1 has been achieved for collisions of OH radicals with rare gas atoms [13][14][15]. This resolution is mainly limited by the velocity and angular spread of the atomic collision partner, and is too low to experimentally resolve scattering resonances.…”

“…Early calculations [17,18] on rotationally inelastic scattering of N 2 molecules with He atoms have shown that resonances occur at low collision energies, but the experimental verification of these predictions was not yet possible. Collisions of OH(X 2 Π) with rare gases have emerged as paradigms of scattering of an open-shell molecule with an atom [13,15,[19][20][21][22][23][24]. The OH-rare gas systems are good candidates for the observation and analysis of resonances in rotationally inelastic collisions because the collision energy can be reduced by Stark deceleration of the OH beam.…”

Stark Deceleration of NO Radicals

“…The advantages of increased interaction times afforded by slowly moving molecules have also been exploited in high-resolution spectroscopy and metrology [4][5][6]. In crossed molecular beam experiments, these beams offer the possibility to study molecular collision processes as a function of the collision energy with a high intrinsic energy resolution [7][8][9][10][11].…”