Experimental Evidence on the Mechanism of Dissociative Electron Attachment to Formic Acid

Abstract

Two mechanisms for dissociative electron attachment in HCOOH, the formation of HCOO À þ H, were proposed in the literature: (i) via a direct electron attachment into a à resonance, augmented by dipole binding of the incident electron [G. A. Gallup et al., Phys. Rev. A 79, 042701 (2009)], and (ii) with the 1.8 eV à resonance as a doorway state, linked to the products by symmetry lowering-distortion of the temporary anion, primarily the C-H bond, from the planar symmetry [T. N. Rescigno et al., Phys. Rev. Lett. 96, 213201 (2006)]. The later mechanism implies a reduction of the cross section upon deuteration of the hydrogen bonded to the C atom, whereas the former mechanism would leave the cross section unaffected. Our experimental absolute cross sections for the four isotopomers of formic acid show that deuteration on the C atom reduces the cross section value only marginally (by 12%) compared to deuteration on the O atom (reduction by a factor of 16), and thus favor mechanism (i).

Electron attachment properties of c-C4F8O in different environments

“…It is obtained as a combination or the error of the present relative measurements (± 15%) and of the error of the absolute cross sections used for normalization. The latter is taken as ± 15% in view of the results from various groups listed in [20]. The electron-beam resolution in the current experiment is approximately 200 meV.…”

“…The shape of the O − peak is also used to determine the energy resolution of the electron beam as described in [18]. The absolute cross sections are calibrated using two independent reference values: the O − from CO 2 [19] and HCOO − from HCOOH [20]. The uncertainty of the obtained cross sections is ±20% (two standard deviations).…”

“…Thus, the measurements in the c-C 4 F 8 O/Ar mixture correspond rather to the regime of saturated three-body attachment (ii). In this case, the saturated three-body attachment rate coefficient k sat can be obtained as (k 0 eff − k eff )/r from equation (20). However, the calculation of k 0 eff in the c-C 4 F 8 O/Ar mixture is probably imprecise, because the drift velocity measured in the c-C 4 F 8 O/Ar mixture indicates that the EEDF deviates from the EEDF of pure Argon, as mentioned in section 3.3.…”

Complex internal rearrangement processes triggered by electron transfer to acetic acid

“…Acetic acid and formic acid have been studied by DEA experiments [22][23][24] where the main focus was given on the dehydrogenated parent anion formation. Meanwhile, DEA theoretical calculations of Rescigno et al [25] have shown that upon electron capture, formic acid proceeds through a π* C=O resonance leading to OH excision.…”

Theory of dissociative electron attachment: Biomolecules and clusters

“…In spite of the DR2013 success of this approach, particularly in description of VFRs, and in spite of the excellent agreement with experiments on formic acid [27], several objections were made with regard to the existence of the * resonance in these systems. Indeed the standard Breit-Wigner parametrization of the scattering eigenphases did not allow for detection of a low-energy * resonance in formic acid [28], uracil [29][30][31] or glycine [32].…”