A selective discussion of electron attachment to molecules is presented with emphasis on recent studies of SF6, carried out with a novel laser photoelectron attachment (LPA) method in the energy range 0·1-170 me V with an effective energy resolution around 0·1 me V near threshold.

Using resonant two-photon ionization of metastable rare gas atoms Rg(mp 5(m + 1)s 3P2,0) in a collimated beam by two transverse cw dye lasers, we have performed a comprehensive high resolution study of the odd Rg(ns',J =0,1) autoionization resonances of all the heavier rare gases Rg--Ne, Ar, Kr and Xe. In this way, we have determined the variation of the nearly n-independent reduced resonance widths F, = n*3. Fn (n*= effective quantum number) with atomic size andfor the first time -with the angular momentum J for all Rg. The reduced widths for the Rg(ns', J = 1) resonances vary by about a factor of three, being lowest for Ne(371 cm -1) and largest for Kr(l185 cm-1). Compared to J = 1, the Rg(ns', J =0) resonances are three times narrower for Ne, but up to two times broader for Ar, Kr, and Xe. The results of ab initio calculations for the widths are reported, in which the relevant transition matrix elements are carefully evaluated. Good overall agreement of the calculated widths with the experimental data is achieved. For Rg(ns', J = 0), the first order s'-d coupling amplitude provides a satisfactory description only for Rg = Ne, whereas for Rg = Ar-Xe, correlation effects are important. For Rg(ns', J = 1), the additional amplitudes due to s'-d exchange coupling and due to s'-s decay are found to be of varying importance with atomic number. Destructive interference between the different amplitudes and the influence of Rg(ns', J = i)-Rg(nd', J --t) coupling are responsible for the fact that the (ns', J = 1) resonances are narrower than the (ns', J = 0) resonances for Ar, Kr, and Xe.

By combination of two independent approaches, nuclear resonant inelastic X-ray scattering and first-principles calculations in the framework of density functional theory, we demonstrate significant changes in the element-resolved vibrational density of states across the first-order transition from the ferromagnetic low temperature to the paramagnetic high temperature phase of LaFe 13−x Si x . These changes originate from the itinerant electron metamagnetism associated with Fe and lead to a pronounced magnetoelastic softening despite the large volume decrease at the transition. The increase in lattice entropy associated with the Fe subsystem is significant and contributes cooperatively with the magnetic and electronic entropy changes to the excellent magnetoand barocaloric properties.

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