ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
We present differential cross section (DCS) measurements for scattering of HF by Ar. These crossed-beam experiments employ rotational state sensitivity, allowing determination of the DCS as a function of the scattered HF rotational state. The initial HF rotational distribution is generated by nozzle expansion, without further state selection. Its composition is mostly J=0 and J=1, with small admixtures for J〉1. The DCS for each final state J' is measured using a stabilized cw HF chemical laser, in conjunction with a rotatable liquid He-cooled bolometer. Measurable signals are obtained for scattering into 0≤J'≤5, where J'=6 is the thermodynamic limit for our collision energy of 120 meV. The measured DCS's show a strong forward peak, largely from elastic scattering. In addition, the DCS's evolve from a broad shoulder in the θ≈25°–40° region for J'=0—through a flattening of the wide-angle scattering for J'=2 and J'=3—to an increase in the scattering beyond ∼40° for J'=4. The DCS for scattering into J'=5 also shows increased intensity at wide scattering angles, but its onset is delayed until ∼70°. These features are shown to be independent of the laboratory → center-of-mass kinematic transformation. The wide-angle scattering into J'=4 and J'=5 corresponds to transferring up to 40% and 60%, respectively, of the available kinetic energy into HF rotation. Since the center-of-mass scattering angles are up to ∼110°, we interpret the observed features for J'=4–5 in terms of rotational rainbow scattering from the hard core of the HF+Ar potential energy surface. The origin of the shoulder for J'=0 scattering is less clear, but it may arise from the strongly anisotropic nature of the HF+Ar van der Waals attraction.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.460654
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