Experimental and computational study of HF+Xe scattering

Abstract

Crossed molecular beam experiments have been performed measuring angular distributions I (ϑ) of HF(¹Σ⁺) scattered off Xe(¹S₀) at collision energies of 0.044 and 0.153 eV. The I (ϑ) show rainbow and supernumerary rainbow structure, with diffractive oscillations just being resolved in the low energy data. A spherically symmetric potential V₀(R) is fit to the data with well depth and minimum position 0.016 eV and 3.77 Å. Using this V₀(R), four model potential surfaces V (R,γ) are constructed and scattering calculations are performed employing the centrifugal sudden approximation. The calculations treat HF as a rigid rotor and use a collision energy of 0.044 eV. The calculations emphasize the role of the initial rotational state as well as the effect of the type and degree of anisotropy of V (R,γ) upon total and state‐to‐state center‐of‐mass differential cross sections. In particular, it is found that when V (R,γ) is strongly attractive for one limited range of atom–diatom orientations, the elastically scattered rainbow is shifted to larger angles compared to the rainbow from V₀(R) scattering—if the initial rotational state j_in=0. For j_in=1 and 2 the V (R,γ) scattering tends to resemble that for V₀(R). Because the j_in distribution in the HF beam is not well characterized, and because it is shown that very similar total differential cross sections at one energy can be generated from qualitatively different V (R,γ) with similar V₀(R), even for the same j_in, conclusions about the HF–Xe anisotropy of V (R,γ) from I (ϑ) are precluded. However, the extracted V₀(R) is thought to be realistic based on the consistency of fits to the two I (ϑ) at significantly different collision energies and the likelihood of a relatively high rotational temperature of the HF beam due to heating of the nozzle source.