Imaging quantum stereodynamics through Fraunhofer scattering of NO radicals with rare-gas atoms

Abstract

Stereodynamics describes how the vector properties of molecules, such as the directions in which they move and the axes about which they rotate, affect the probabilities (or cross-sections) of specific processes or transitions that occur on collision. The main aspects of stereodynamics in inelastic atom-molecule collisions can often be understood from classical considerations, in which the particles are represented by billiard-ball-like hard objects. In a quantum picture, however, the collision is described in terms of matter waves, which can also scatter into the region of the geometrical shadow of the object and reveal detailed information on the pure quantum-mechanical contribution to the stereodynamics. Here we present measurements of irregular diffraction patterns for NO radicals colliding with rare-gas atoms that can be explained by the analytical Fraunhofer model. They reveal a hitherto overlooked dependence on (or 'propensity rule' for) the magnetic quantum number m of the molecules, and a previously unrecognized type of quantum stereodynamics that has no classical analogue or interpretation.

Observation of correlated excitations in bimolecular collisions

“…We found that the angular momenta of two excited molecules indeed become quantum entangled, leading to a violation of Bell's inequalities that may in principle be probed experimentally (see Supplementary section: Entanglement). This entanglement occurs especially for the Fraunhofer diffraction oscillations in the differential cross sections at small scattering angles (11).…”

“…State-to-state cross sections (5), steric effects (?, 6), as well as vector correlations between pre and post-collision properties (8)(9)(10) can be precisely measured, and in general show excellent agreement with predictions based on full quantum mechanical calculations. During the last decades, this wealth of experimental and theoretical studies has revealed how energy and angular momentum is transferred between the collision partners, although surprising discoveries continue to be made (11). Sophisticated qualitative and intuitive models have been developed that explain general trends in the scattering cross sections, which can also be determined quantitatively by near-exact quantum mechanical treatments.…”

Optimizing the density of Stark decelerated radicals at low final velocities: a tutorial review

“…A number of techniques for the generation of cold molecules has been developed [1-5] among which Stark deceleration is one of the most important [3,[6][7][8]. This method finds a broad range of applications in spectroscopy [9][10][11][12], collision-dynamics studies [13][14][15][16][17][18][19][20][21][22][23][24][25][26] and trap loading experiments [27][28][29][30][31][32][33]. The principle of Stark deceleration has been well documented [2,3], and a number of operation schemes have been developed for the optimization of Stark-decelerated molecular beams in different types of experiments [34][35][36][37].…”

Cold Collisions in a Molecular Synchrotron

“…Of particular interest are resonances of the collision cross section as a function of the collision energy [7][8][9][10]. The position and shape of these resonances are very sensitive to the exact shape of the PES and thus serve as precise tests of our understanding of intermolecular forces.The ability to control the velocity of molecules using time-varying electric fields has allowed studies of inelastic collisions of OH and NO molecules with rare gas atoms at low collision energies [11][12][13][14]. Using cryogenically cooled beams under a small (and variable) crossing angle, inelastic collisions of O 2 and CO with H 2 and helium at energies between 5 and 30 K have been studied [15].…”

“…The ability to control the velocity of molecules using time-varying electric fields has allowed studies of inelastic collisions of OH and NO molecules with rare gas atoms at low collision energies [11][12][13][14]. Using cryogenically cooled beams under a small (and variable) crossing angle, inelastic collisions of O 2 and CO with H 2 and helium at energies between 5 and 30 K have been studied [15].…”