Electron-impact dissociation ofCH+ions: Measurement ofC+fragmen

Abstract

Absolute cross sections for electron-impact dissociation of CH ϩ producing C ϩ fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 10% near the cross-section peak. Although the measured energy dependence agrees well with two sets of storage ring measurements, the magnitude of the present results lies about 15-25 % below the other results at the crosssection peak near 40 eV. Below 10 eV, the present data tend to exceed the storage ring data, consistent with the presence of excited states in the CH ϩ ion beam. For energies above 29 eV, the cross sections should also include contributions from dissociative ionization, though no clear onset of this channel is evident in any of the three sets of measured data.

R-matrix study of electron impact excitation and dissociation of CH+ions

“…The contribution of cross sections corresponding to 'pure' electronic excitation were estimated using Franck-Condon factors and these were then subtracted out to get the dissociation cross sections. Our results agree reasonably well with the measurements of Bannister et al (2003) from the threshold (10 eV) to about 18 eV and are within 20% of the measured values. Above this we would expect our results underestimate the cross section due to neglect of higher lying states which were not included in our calculations.…”

“…A Multi Channel Quantum Defect Theory (MQDT) study of dissociative recombination of CH + and its isotopologue CD + was reported by Carata et al (2000) which were not in very good quantitative agreement with an earlier experimental study reported by Amitay et al (1996). Bannister et al (2003) reported an experimental study of the electron impact dissociation of CH + to the asymptotic states C + ( 2 P ) + H( 2 S). They measured absolute cross sections for electron impact dissociation of CH + ions producing C + ions.…”

“…The X 1 Σ + , a 3 Π, A 1 Π and c 3 Σ + states dissociate to the fragments C + ( 2 P ) + H( 2 S), while the b 3 Σ − and d 3 Π states dissociate into the fragments C( 3 P ) + H + . Experiments measuring the absolute cross sections for electron impact dissociation of CH + ions producing C + ions were reported by Bannister et al (2003). Figure 3 shows the results of Bannister et al (2003) together with our theoretical results for the dissociation to the asymptotic states C + ( 2 P ) + H( 2 S) (thick curve), C( 3 P ) + H + (thin curve) and their sum (topmost curve).…”

“…Experiments measuring the absolute cross sections for electron impact dissociation of CH + ions producing C + ions were reported by Bannister et al (2003). Figure 3 shows the results of Bannister et al (2003) together with our theoretical results for the dissociation to the asymptotic states C + ( 2 P ) + H( 2 S) (thick curve), C( 3 P ) + H + (thin curve) and their sum (topmost curve). Our results were calculated with the assumption that all excitations from the X 1 Σ + ground state to the states, dissociating to a particular asymptote, above the corresponding dissociation threshold result in dissociation.…”

Electrostatic ion beam trap for electron collision studies

“…Energy-resolved studies in this field were performed using crossed electron and molecular-ion beams, ranging from the earliest works in the late 1970s 1,2 and up to very recent studies. [3][4][5] However, internal excitation of the molecular ions introduces substantial ambiguities in the interpretation of these experiments, especially at collision energies of the order of 10 eV or below. During the last decade, studies of electron impact processes on internally cold molecular ions could be realized by using magnetic heavy-ion storage rings.…”