Formation of negative hydrogen ions in 7-keV OH++Arand OH++acetone collisions: A general process for H-bearing molecular species

Abstract

We demonstrate that the formation of negative hydrogen ions (H -) occurs in a wide class of atomic and molecular collisions. In our experiments, Hemission from hydroxyl cations and acetone molecules was observed in keV-energy collisions. We show that hydride (H -) anions are formed via direct collisional fragmentation of molecules, followed by electron grabbing by fast hydrogen fragments. Such general mechanism in hydrogen-containing molecules may significantly influence reaction networks in planetary atmospheres and astrophysical media and new reaction pathways may have to be added in radiolysis studies.

Formation of anions and cations via a binary-encounter process inOH++ Ar collisions: The role of dissociative excitation and statistical aspects

“…2(b) of Ref. [17], our scaled cross-section curve for H scattering on Ar nicely connects the two sets of results and matches the cross sections measured at small angles (0.3°-3°). It was surprising that the two-body picture could satisfactorily describe such a wide class of collisions, including collisions leading to small scattering angles (soft collisions at large impact parameter) in which the energy transfer is too small to create an H − ion from the ground state of the H 2 + radical.…”

“…Hence, by taking into account the different sources of errors, the uncertainty of the present calibration in absolute scale is about 60%, which is less than it was in our previous work [17], in which the calibration relied on earlier measurements. The present calibration leads to cross sections for H − production 1.8 times lower than those in Ref.…”

“…4, the angular dependence of both H − and H + cross sections is highly similar to that of theoretical cross sections for elastic scattering of H on Ar. (Details on the scattering cross-section calculation are given in our previous paper [17]). When multiplied by an appropriate factor, the theoretical curves match fairly well the experimental data in the entire angular range (Fig.…”

“…The same experimental method has been described in a previous work [17]. It consists of a crossed-beam type experiment in the gas phase.…”

“…Hence, it was concluded that the fraction of the scattered H centers which become negatively charged is independent of the scattering angle, and thus, barely depends on the impact parameter and on the momentum transfer. Accordingly, the distribution of the final charge states of the fragments was suspected to be akin to a statistical distribution [17]. Upon this, the question * zjuhasz@atomki.hu † jean-yves.chesnel@ensicaen.fr arises whether a similar angular independence applies for the fraction of positively charged fragments, too.…”