Cold and ultracold NH-NH collisions in magnetic fields

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Elastic and spin-changing inelastic collision cross sections are presented for cold and ultracold magnetically trapped NH. The cross sections are obtained from coupled-channel scattering calculations as a function of energy and magnetic field. We specifically investigate the influence of the intramolecular spin-spin, spin-rotation, and intermolecular magnetic dipole coupling on the collision dynamics. It is shown that 15 NH is a very suitable candidate for evaporative cooling experiments. The dominant trap-loss mechanism in the ultracold regime originates from the intermolecular dipolar coupling term. At higher energies and fields, intramolecular spin-spin coupling becomes increasingly important. Our qualitative results and conclusions are fairly independent of the exact form of the potential and of the size of the channel basis set.

Efficient method for quantum calculations of molecule-molecule scattering properties in a magnetic field

“…In order to verify the accuracy of our method and computations, we also repeated the calculations of Janssen et al [37] for 15 Figure 5 presents the magnetic field dependence of γ for 15 NH -15 NH collisions computed for several collision energies. In the limit of low collision energies, the elastic cross sections are energy independent and the inelastic cross sections are inversely proportional to the collision velocity [55].…”

“…As in the previous studies of 15 NH-15 NH collisions [37,48,49], we assume that all three spin states of the 15 NH-15 NH complex are described by the nonreactive quintet surface, i.e. [50].…”

“…While J is not conserved in the presence of an external field, the total angular momentum representation allows for a much more efficient truncation of the basis set than the uncoupled representation [41]. In the present work, we use the total angular momentum representation to extend the 15 NH -15 NH scattering calculations of Janssen et al [37] in order to compute the scattering cross sections with a much larger basis set including up to 7 rotational states of 15 NH. The imidogen radical (NH) is currently studied in several experiments aiming at the production of ultracold molecules [17,34,[42][43][44][45].…”

“…) collisions in a magnetic field [36] and NH( 3 Σ) -NH( 3 Σ) collisions in a magnetic field [37]. These calculations are based on the fully uncoupled space-fixed (SF) representation of the scattering wave functions [38,39], which results in prohibitively large basis sets and precludes fully converged computations with realistic intermolecular potentials.…”

Sympathetic cooling of fluorine atoms with ultracold atomic hydrogen

“…The inelastic cross sections are actually smaller than for spin-stretched collisions at a low energy, because the kinetic energy releases are lower and there is more centrifugal suppression. At 1 G the centrifugal suppression is so strong that a different mechanism takes over: the weak dipolar interaction can drive long-range inelastic collisions that take place outside the centrifugal barrier [56,57], producing H a and F b or F c ; Fig. 4(b) shows that this is the dominant low-energy mechanism at 1 G.…”