Dissociative Excitation Cross Sections Research Articles

Theoretical Investigation of Electron Impact Scattering on Imidazole.

This study presents the results of electron scattering calculations on a biologically important molecule, imidazole, using the UK molecular R-matrix method. The R-matrix calculations are performed using SE, SEP, and CC models, and the resonance detected in the present SEP model is found to be in better agreement with available experimental data than previous theoretical data. The study also reports an inelastic scattering cross section, which comprises dissociative electron attachment (DEA), excitation, and ionization cross section, for the first time. The total scattering cross sections are also reported for the first time. We confirm the presence of the two well-known π* shape resonances predicted earlier experimentally. Due to the scarcity of total scattering cross section (TCS) data for imidazole, we have compared the TCS of imidazole with its isoelectronic target isoxazole and drawn important conclusions. A comparison among the resonances of imidazole with those of isoxazole helps us to conclude that electron attachment to π* molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds. The comprehensive electron scattering studies presented in this work are expected to provide a deeper understanding of electron-induced biochemical processes and fill gaps in the available data. Furthermore, this study is anticipated to inspire further investigations on imidazole and other five-membered heterocyclic ring molecules, which have significant applications in medicine.

Vibrationally resolved NO dissociative excitation cross sections by electron impact

A theoretical investigation of the dissociative excitation by electron impact on the NO molecule is presented, aiming to make up for the lack of data for this process in the literature. A full set of vibrationally-resolved cross sections and corresponding rate coefficients are calculated using the local-complex-potential approach and five resonant states of NO−.

Dissociative Excitation of Odd Sextet Levels of the Cobalt Atom in Collisions of Electrons with Cobalt Dibromide Molecules

Dissociative excitation of odd sextet levels of the cobalt atom in collisions of electrons with cobalt dibromide molecules was experimentally studied. At an energy of incident electrons of 100 eV, 53 dissociative excitation cross sections were measured; in five cases, there were blends. In the electron energy range of 0–100 eV, the optical excitation functions for transitions from 10 sextet levels of CoI were determined. The main feature of the studied levels was their long lifetime, because of which some of the excited atoms leave the field of view of the optical system without any emission of radiation.

Calculations of positron scattering on the hydrogen molecular ion

Positron scattering from the vibrational ground state of the hydrogen molecular ion has been investigated using the single-centre convergent close-coupling (CCC) method. Cross sections for dissociative excitation, dissociative ionisation, total inelastic scattering, and proton production have been calculated at incident positron energies from 10 to 500 eV. For this energy range the mass stopping power and mean excitation energy have also been calculated for both the positron and electron cases. Since there are no experiments or other calculations for positron scattering on the hydrogen molecular ion, the obtained results have been compared with corresponding CCC results for positron collisions with He+ and electron collisions with . Comparative analysis allows to estimate the quality of the approximations used in the present calculations.

Vibrationally resolved excitation, dissociation, and rotational cross sections of NH radical by electron-impact using the R-matrix method

The ab initio R-matrix method is employed to study the electronic excitation of low-lying target states, the dissociation cross sections, and the rotational cross sections of the NH radical by electron impact for energies up to 15 eV. We have included dynamic interaction in our scattering model that uses close coupling formalism. There are 24 target states whose vertical excitation energies are below 15 eV, which are included in the trial wavefunction of the entire scattering system. In our scattering model, two electrons are frozen in the 1σ2 configuration and the remaining six electrons are free to move in the molecular orbitals 2σ 3σ 4σ 5σ 6σ 1π and 2π. The cc-pVTZ Dunning basis sets are used to optimize the target structure and electron scattering. The vibrationally resolved cross sections for transition from the ground state X 3Σ− to excited state c 1Π are computed by scaling the corresponding electronic excitation cross section by Franck-Condon factors. These factors are evaluated by using accurate potential energy curves of the ground state and the c excited state. We have compared the excitation cross section for the optically allowed transition X 3Σ− to A 3Π computed using our scattering model with the corresponding cross section evaluated in Born approximation, and the agreement is quite good indicating that for a reasonably high transition moment and a low threshold of the excited state, the effects of correlation and polarization are not very significant. The dissociative excitation cross section by electron impact into atomic fragments N and H is also shown which are caused mainly by c 1Π and a purely repulsive state 1 5Σ−. We have also shown that the vibrational cross section evaluated in Born approximation for the fundamental transition 0–1 of the ground state is quite small as compared to the rotational cross sections. The rotational cross sections are computed for j = 0 to j′ = 0–5, and it is shown that the dipole induced transition is predominant with an order of magnitude higher than the pure rotational 0–0 cross section. We have detected many low-lying core-excited shape resonances and provided their resonance parameters which form an important input to estimate dissociative electron attachment cross sections.

Dissociative Excitation of Odd Triplet Levels of a Nickel Atom by Collisions of Electrons with Nickel Dibromide Molecules

The dissociative excitation of the odd triplet levels of a nickel atom by the collisions of electrons with nickel dibromide molecules is investigated using extended crossing beams and recording the optical signal of the excited atoms. In all, 50 excitation cross-sections of Ni I spectral lines are measured at an electron energy of 100 eV. Nine optical excitation functions (OEFs) are recorded in a range of electron energies of 0–100 eV. The obtained data on the dissociative excitation cross-sections of the spectral lines are used for the calculation of the excitation cross-sections of the energy levels as well as the contribution from the cascade transitions. The possible channels of dissociative excitation which manifest themselves in the region of low electron energies (E < 22 eV) are discussed.

Electron-impact dissociative excitation cross sections for singlet states of molecular hydrogen

We report cross sections for electron-impact dissociative excitation of the $B{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}$, $C{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}$, $D{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}$, ${B}^{\ensuremath{'}}{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}$, and $E,F{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ singlet states of molecular hydrogen from all ${v}_{i}=0--14$ vibrational levels of the ground $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ state. Calculations are performed using the adiabatic-nuclei convergent close-coupling method formulated in prolate spheroidal coordinates from threshold to 500 eV. Agreement with previous calculations varies with transition and impact energy, ranging from excellent to poor. Agreement with available experiment is generally good.

Dissociative Excitation of the Odd Sextet Levels of the Cobalt Atom by Collisions of Electrons with Cobalt Dichloride Molecules

Inelastic collisions of slow electrons with cobalt dichloride molecules, leading to the formation of excited cobalt atoms in odd sextet states, are experimentally studied. At an incident electron energy of 100 eV, thirty six dissociative excitation cross sections are measured for levels belonging to the z6D°, z6F°, and z6G° terms. In the electron energy range of 0–100 eV, ten optical excitation functions are recorded. The full cross sections for the dissociative excitation of the cobalt atom levels and the contribution of cascade transitions to their population are determined. The cross sections for electron–molecule and electron–atom collisions are compared.

Theoretical resonant electron-impact vibrational excitation, dissociative recombination and dissociative excitation cross sections of ro-vibrationally excited BeH+ ion

A theoretical study of resonant vibrational excitation, dissociative recombination and dissociative excitation processes of the beryllium monohydride cation, BeH+, induced by electron impact, is reported. Full sets of ro-vibrationally-resolved cross sections and of the corresponding Maxwellian rate coefficients are presented for the three processes. Particular emphasis is given to the high-energy behaviour. Potential curves of , and symmetries and the corresponding resonance widths, obtained from R-matrix calculations, provide the input for calculations which use a local complex-potential model for resonant collisions in each of the three symmetries. Rotational motion of nuclei and isotopic effects are also discussed. The relevant results are compared with those obtained using a multichannel quantum defect theory method. Full results are available from the Phys4Entry database.

Dissociative excitation of the 2 S°, 2 P°, and 2 D° levels of the cobalt atom in collisions of slow electrons with cobalt dibromide molecules

The dissociative excitation of the odd doublet S, P, and D levels of the cobalt atom in collisions of slow electrons with cobalt dibromide molecules was studied experimentally. Eighty six dissociative excitation cross-sections were measured at an exciting electron energy of 100 eV. Two optical excitation functions were recorded at electron energies in the range 0–100 eV. The total dissociative excitation cross-sections were calculated for 20 levels based on the obtained results. The cross-sections of the formation of excited cobalt atoms in e–Co, e–CoBr2, and e–CoCl2 collisions were compared.

Dissociative excitation of the singly charged manganese ion in collisions of electrons with manganese diiodide molecules

The dissociative excitation of the singly charged manganese ion in collisions of electrons with MnI2 molecules is experimentally studied. At exciting electron energy of 100 eV, 16 dissociative excitation cross sections were measured. The studied transitions occur within the quintet and septet term systems in the absence of intercombination transitions. The measured values of the cross sections are compared to similar values obtained previously in studies of e–MnCl2 and e–MnBr2 collisions.

Dissociative excitation and vibrational excitation of Cl2+

SynopsisThe cross sections for resonant dissociative excitation and vibrational excitation of Cl+2 molecular ion in the 0-10 eV region are calculated by solving a driven Schrödinger equation for the four lowest resonant states of all symmetries.

Dissociative recombination and excitation of D5+ by collisions with low-energy electrons

We report results from high-resolution studies of D5+ cluster ion collisions with low-energy electrons performed in a heavy ion storage ring. Absolute dissociative recombination (DR) and dissociative excitation (DE) cross sections were determined for the energy range from 0.0005 to 20 eV. The DR cross sections were exceedingly large at low energies, and DR resulted in efficient internal energy redistribution and pronounced fragmentation with two main product channels: D2+3D (0.62 ± 0.03) and 2D2+D (0.35 ± 0.01). The DR and DE cross sections were comparable in the energy range from 0.2 to 20 eV, which suggest that the two processes follow similar dynamics and are competing outcomes of the ion–electron interaction. A simple picture of the recombination process of D5+ which captures the essential physics is suggested.

Dissociative Excitation of Nickel Atom Spectral Lines in e–NiBr2 Collisions (Transitions from Even Levels Belonging to 3d84s5s and 3d84s4d Configurations)

Dissociative excitation of nickel atoms in e‐NiBr2 collisions studied by the method of extended crossing beams with registration of optical radiation of excited atoms. In this article the results are presented, related to dissociative excitation cross-sections of even parity states belonging to 3d 8 4s5s and 3d 8 4s4d configurations. Obtained data compared with direct excitation crosssections of the same levels in electron-atom collisions.

Cross sections for dissociative ionization and dissociative excitation of H 2 + by single photon absorption

The photo-absorption cross sections for the dissociative ionization and dissociative excitation of H 2 + are calculated for photon polarization parallel and perpendicular to the internuclear axis. The wavefunctions for the initial and final states are prepared using the Born-Oppenheimer approximation. For dissociative ionization, the cross section and angular distribution of photo-electrons are compared with those calculated with the fixed-nuclei approximation. For dissociative excitation, the cross sections for H (N = 1∼4) productions are shown.

Dissociative excitation of even levels of the singly charged yttrium ion in collisions of slow electrons with yttrium tribromide molecules

The method of extended crossing beams in conjunction with optical spectroscopy is used to study the dissociative excitation of even levels of YII in e-YBr3 collisions. At the exciting electron energy of 100 eV, 38 dissociative excitation cross sections are measured. Comparison of these cross sections with the cross sections for direct excitation in e-Y collisions shows that, for all the investigated even levels of YII, dissociative excitation is more efficient than direct one.

Electron-impact dissociation of HeH+: absolute cross sections for the production of Heq+ (q = 1–2) fragments

Absolute cross sections have been measured for electron-impact dissociative excitation and ionization of the helium-hydride ion (HeH+) leading to the formation of helium ions Heq+ (q = 1–2). Measurements have been performed for electron energies ranging from the respective thresholds up to 2.5 keV. For He+ production, the maximum absolute cross section for dissociative excitation is found to be (2.5 ± 0.2) ×10−17 cm2 (around 40 eV), while for dissociative ionization, it is found to be (2.1 ± 0.1) ×10−17 cm2 (around 135 eV). For He2+ production, only the inclusive absolute cross section is presented, without attempting to isolate any distinct contribution, and it is measured to be (2.6 ± 0.2) ×10−19 cm2 (around the maximum, 195 eV). Appearance energies for He+ and He2+ are determined to be (11.2 ± 0.5) eV and (66.5 ± 1.0) eV, respectively. Kinetic energy release and angular distributions are obtained, at specific incident electron energies.

Dissociative excitation of even triplet and quintet levels of the iron atom in collisions of electrons with iron diiodide molecules

The method of extended crossing beams is used to study inelastic collisions of slow electrons with iron dichloride molecules. The dissociative excitation of even triplet and quintet levels of the iron atom at the incident electron energy of 100 eV is examined. The resulting dissociative excitation cross sections are compared to the cross sections of the excitation of FeI in electron-atom collisions.

Formation of excited singly charged barium ions in collisions of slow electrons with barium dibromide molecules

The method of extended crossing beams is used to study inelastic collisions of slow electrons with barium dibromide molecules. The resulting optical emission spectrum contains only the spectral lines of the singly charged barium ion. At an exciting electron energy of 100 eV, the cross sections of dissociative excitation for nine spectral lines of BaII are measured; for all these lines, the optical excitation functions over an electron energy range of 0 to 100 eV are recorded. The possible channels of the dissociative excitation of BaII are discussed.

Studies of electron-impact dissociative excitation and ionization using the crossed electron-ion beams technique

Absolute cross sections for heavy ion fragment production due to electron-impact dissociation of XH2+ (X = B, C, N, O, F), N2D+ and O3+ have been investigated with the crossed electron-ion beams technique in the energy range 3 – 100 eV. This energy regime covers the dissociative excitation and ionization processes. Two and three-body dissociation channels are observed in these systems and marked resonant-like structure is also observed in the dissociative excitation channels of some systems. It is unclear if direct excitation or resonant capture processes lead to these enhanced dissociative excitation cross sections.