Absolute cross sections for dissociative electron attachment to HCN and DCN

We performed nuclear dynamics calculations on HCN and DCN to study the isotope effect in dissociative electron attachment. Our previous calculations at 333 K led to a ratio σ (CN − /HCN) /σ (CN − /DCN) of about 13, which is significantly higher than recent experimental findings. This discrepancy is attributed to the neglect of correlation and polarization effects in the scattering calculation performed. We carried out a relaxed-self-consistent field calculation to determine the variation of the resonance parameters under these effects. We observe a shift in the positions of the shape resonance as well as a narrowing of the autoionization widths resulting in an isotope ratio of 3.2 at T = 333 K; in closer agreement with the measured value.

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“…7, respectively, for HCN and DCN. In these figures, further compare the present results to the experimental values of May et al [1].…”

Section: Dea Cross Sectionsupporting

confidence: 76%

“…Recently, May et al conducted a time-of-flight ion spectrometry experiment to measure the isotope effect in dissociative electron attachment (DEA) to HCN [1]. The authors measured a σ (CN − /HCN) /σ (CN − /DCN) ratio of 2.76 at 333 K below 3 eV in electron energy.…”

Section: Introductionmentioning

confidence: 99%

Isotope effect in dissociative electron attachment to HCN

Chourou

Orel

2011

Phys. Rev. A

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“…Burrow et al 5 reported electron transmission spectra and identified a low-lying shape resonance. More recently, May et al 6 reported absolute partial cross sections for the formation of CN − using a timeof-flight ion spectrometer. Calculations were also performed a while ago by Jain and Norcross 7 using a model potential method and by Varambhia and Tennyson who applied the R-matrix technique.…”

Section: Introductionmentioning

confidence: 99%

Electron scattering cross sections from HCN over a broad energy range (0.1–10 000 eV): Influence of the permanent dipole moment on the scattering process

Sanz

Fuß

Blanco

et al. 2012

The Journal of Chemical Physics

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G. (2012). Electron scattering cross sections from HCN over a broad energy range (0.1-10 000 eV): Influence of the permanent dipole moment on the scattering process. Journal of Chemical Physics, 137 (12), 124103-1-124103-9. Electron scattering cross sections from HCN over a broad energy range (0.1-10 000 eV): Influence of the permanent dipole moment on the scattering process AbstractWe report theoretical integral and differential cross sections for electron scattering from hydrogen cyanide derived from two ab initio scattering potential methods. For low energies (0.1-100 eV), we have used the symmetry adapted-single centre expansion method using a multichannel scattering formulation of the problem. For intermediate and high energies (10-10 000 eV), we have applied an optical potential method based on a screening corrected independent atom representation. Since HCN is a strong polar molecule, further dipole-induced excitations have been calculated in the framework of the first Born approximation and employing a transformation to a space-fixed reference frame of the calculated K-matrix elements. Results are compared with experimental data available in the literature and a complete set of recommended integral elastic, inelastic, and total scattering cross sections is provided from 0.1 to 10 000 eV. © 2012 American Institute of Physics. We report theoretical integral and differential cross sections for electron scattering from hydrogen cyanide derived from two ab initio scattering potential methods. For low energies (0.1-100 eV), we have used the symmetry adapted-single centre expansion method using a multichannel scattering formulation of the problem. For intermediate and high energies (10-10 000 eV), we have applied an optical potential method based on a screening corrected independent atom representation. Since HCN is a strong polar molecule, further dipole-induced excitations have been calculated in the framework of the first Born approximation and employing a transformation to a space-fixed reference frame of the calculated K-matrix elements. Results are compared with experimental data available in the literature and a complete set of recommended integral elastic, inelastic, and total scattering cross sections is provided from 0.1 to 10 000 eV.

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“…An ab initio calculation of DEA to HCN [33,34] (validated experimentally [35]) led to the surprising finding that although the electronic structure is the same as in the case of acetylene, and also the potential surfaces of the two anions are similar (i.e., an energy barrier is encountered for dissociation in linear geometry but may be by-passed by bending the Ã anion out of linearity), a dynamics calculation revealed that the hydrogen prefers to tunnel through the barrier rather than traveling around it in HCN. This could also happen for the O-H hydrogen in formic acid; the dissociation of the Ã resonance would then proceed without involvement of the C-H hydrogen and would also explain the present experimental finding.…”

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confidence: 99%

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

et al. 2013

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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 Ã 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 Ã 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).

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Absolute cross sections for dissociative electron attachment to HCN and DCN

Cited by 27 publications

References 25 publications

Isotope effect in dissociative electron attachment to HCN

Isotope effect in dissociative electron attachment to HCN

Electron scattering cross sections from HCN over a broad energy range (0.1–10 000 eV): Influence of the permanent dipole moment on the scattering process

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

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