Interaction of NH(XΣ−3) with He: Potential energy surface, bound states, and collisional Zeeman relaxation

Abstract

A detailed analysis of the He-NH((3)Sigma(-)) van der Waals complex is presented. We discuss ab initio calculations of the potential energy surface and fitting procedures with relevance to cold collisions, and we present accurate calculations of bound energy levels of the triatomic complex as well as collisional properties of NH molecules in a buffer gas of (3)He. The influence of the external magnetic field used to trap the NH molecules and the effect of the atom-molecule interaction potential on the collisionally induced Zeeman relaxation are explored. It is shown that minute variations of the interaction potential due to different fitting procedures may alter the Zeeman relaxation rate at ultralow temperatures by as much as 50%.

Bound state spectroscopy of NH–He

“…The potential energy surface of Cybulski et al 3 for the ground state has a well depth of D e Љϭ19.8 cm Ϫ1 . This minimum occurs at the Jacobi coordinates R e ϭ3.35 Å and e ϭ62.3°͑where ϭ0°f or collinear NH-He͒.…”

“…The apparatus used for this work has been described previously. 6 NH radicals were formed in the early stages of the expansion by 193 nm multiphoton dissociation of NH 3 . A carrier gas mixture of He with ͑0.02-0.04͒% NH 3 was used to drive the expansion.…”

“…This cross-section has not been measured, but theoretical calculations 2 indicate that it is a factor of at least 10 5 smaller than the elastic cross section at temperatures in the range of 0.5-1 K. The reliability of this prediction is critically dependent upon the accuracy of the theoretical NH͑X͒-He potential energy surface. This potential was calculated by Krems et al 2 and Cybulski et al 3 The surface exhibits a shallow minimum at long range that is just deep enough to support a bound state of the NH͑X͒-He complex. Hence experimental verification of the existence of this complex, and measurement of its rotational constant, provides a test of the quality of the theoretical potential.…”

Quantum mechanical calculation of the collision-induced absorption spectra of N2–N2 with anisotropic interactions

“…29 The eigenstates of the reference Hamiltonian are determined using the sinc-DVR. 27,28 The shift R shift = −1 a 0 allows the radial basis to accurately sample the repulsive region, which is otherwise only reached by states of very high energy.…”

Zeeman relaxation of MnH (X7Σ+) in collisions withHe3Turpin1, Stoecklin2, Halvick3 2011Phys. Rev. A5170View full textAdd to dashboardCite

“…The buffer gas cooling efficiency depends critically on the ratio of elastic to inelastic collision rates while the inelastic processes leading to trap loss were shown by Krems et al to be produced by the spin-rotation interactions [20] for 2  molecules and are assumed to be due to the spin-spin interaction for  states of higher spin multiplicity. The theoretical studies dedicated to Zeeman relaxation of diatomic molecules in a  state in collisions with 3 He and submitted to a magnetic field are He-O 2 ( 3 ) [21], He+CaH( 2  + ) and Ar+NH( 3   ) [22], He-NH( 3   ) [23,24,25,26] and He-N 2 + ( 2  + ) [27,28,29]. In a recent study, Bakker et al [30] suggested that MnH(X 7   ) is a good candidate to be cooled using buffer gas cooling and stored using magnetic trapping as this molecule has a large magnetic moment, relatively small spin-spin and spin-rotation coupling constants and a large rotational constant.…”