Total and positronium formation cross sections for positron scattering from H₂O and HCOOH

Experimental and theoretical cross sections for positron collisions with 3-hydroxy-tetrahydrofuran

“…In doing so, we find that the magnitude of the TCS we list in Table IV would increase between ∼41% at 1 eV and ∼4.1% at 150 eV. Hence, similar to what we found in our earlier investigations on polar polyatomic molecules, 9,30 we can expect the forward angle scattering effect to play an important role at the lower energies and become progressively less significant towards the higher energies.…”

“…This TCS behavior is predominantly associated with the important role that the large permanent dipole moment and strong dipole polarizability of the target play at low energy in the scattering dynamics. This is not an original observation, as we have previously noticed this same kind of behavior in the low-energy TCS from our earlier studies on polyatomic polar molecules, such as water and formic acid, 30 and THF. 9 The independent work carried out in the last decade at the University of Trento (see, e.g., Refs.…”

Positron scattering from the cyclic ethers oxirane, 1,4-dioxane, and tetrahydropyran

“…Second, we reiterate that the data in Table II are not corrected for the imperfect forward angle discrimination of the spectrometer, which if implemented could see very large increases in the measured TCSs particularly at the lower energies. 38 The low-energy behaviour of the present positronethylene oxide total cross sections was not unexpected, as we have encountered similar trends in our previous work on polar biomolecules, 8-11, 35, 37, 39-41 which we have ascribed to the strong dipole moments and significant dipole polarisabilities of those species. The current positron-C 2 H 4 O TCS shows a largely monotonic decrease in value with increasing positron energy, until first the positronium channel and then the direct ionisation channel successively open.…”

“…This correspondence between α and the TCS should not be regarded as too surprising, as the San Diego group has, for many species, clearly established a link (albeit an empirical one) between the value of their positron binding energies (ε b ) (Ref. 42) and the value of α. Makochekanwa et al, 38 in their study on the positronium formation cross sections of formic acid and water, also observed a link between those cross sections and the dipole polarisabilities of those species. In other words, the importance of the target dipolarisability on the scattering dynamics in positron scattering systems is well established.…”

“…From an experimental perspective, the major cause of the discrepancy is most likely that the present TCSs have not been corrected for forward-angle scattering effects. 31 As Makochekanwa et al 38 showed for H 2 O and HCOOH, which have dipole polarisabilities of significant magnitude and strong permanent dipole moments such as C 2 H 4 O, the correction (increase) in the TCSs, particularly at low incident positron energies, could be large and becoming even greater as you go to progressively lower energies. In principle we could use the present calculated elastic differential cross sections to correct for this effect, however given the level of agreement between theory and experiment for the integrated cross sections in Fig.…”