Atomic and Molecular Radiation Physics

Christophorou, L. G.; Kim, Y.-K.; Fano, U.

doi:10.1119/1.1986794

Cited by 154 publications

(146 citation statements)

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“…Electron exchange makes it possible to change the multiplicity of an electronic state by ±2, thus allowing for instance the transition from an initial singlet ground state to a final triplet excited state. 61 Electron correlation effects at long range are responsible for the induced polarization interaction that arises from virtual excitation of optically allowed electronic transitions (i.e., associated with the dipole moment) of the molecule. 62 When the incident electron energy E 0 exceeds the corresponding transition energies, the electron then suffers inelastic collisions, which transfer and partition its energy among the various electronic excitations.…”

Section: B Electronic Scattering Cross Sectionsmentioning

confidence: 99%

Absolute cross sections for electronic excitations of cytosine by low energy electron impact

Bazin

Michaud

Sanche

2010

The Journal of Chemical Physics

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The absolute cross sections (CS) for electronic excitations of cytosine by electron impact between 5 and 18 eV were measured by electron-energy loss (EEL) spectroscopy of the molecule deposited at low coverage on an inert Ar substrate. The lowest EEL features found at 3.55 and 4.02 eV are ascribed to transitions from the ground state to the two lowest triplet 1 3 A′(π→π*) and 2 3 A′ (π→π*) valence states of the molecule. Their energy dependent CS exhibit essentially a common maximum at about 6 eV with a value of 1.84 × 10 −17 cm 2 for the former and 4.94 × 10 −17 cm 2 for the latter. In contrast, the CS for the next EEL feature at 4.65 eV, which is ascribed to the optically allowed transition to the 2 1 A′(π→π*) valence state, shows only a steep rise to about 1.04 × 10 −16 cm 2 followed by a monotonous decrease with the incident electron energy. The higher EEL features at 5.39, 6.18, 6.83, and 7.55 eV are assigned to the excitations of the 3 3, 1 A′(π→π*), 4 1 A′(π→π*), 5 1 A′(π→π*), and 6 1 A′(π→π*) valence states, respectively. The CS for the 3 3, 1 A′ and 4 1 A′ states exhibit a common enhancement at about 10 eV superimposed on a more or less a steep rise, reaching respectively a maximum of 1.27 and 1.79 × 10 −16 cm 2 , followed by a monotonous decrease. This latter enhancement and the maximum seen at about 6 eV in the lowest triplet states correspond to the core-excited electron resonances that have been found by dissociative electron attachment experiments with cytosine in the gas phase. The weak EEL feature found at 5.01 eV with a maximum CS of 3.8 × 10 −18 cm 2 near its excitation threshold is attributed to transitions from the ground state to the 1 3, 1 A″(n→π*) states. The monotonous rise of the EEL signal above 8 eV is attributed to the ionization of the molecule. It is partitioned into four excitation energy regions at about 8.55, 9.21, 9.83, and 11.53 eV, which correspond closely to the ionization energies of the four highest occupied molecular orbitals of cytosine. The sum of the ionization CS for these four excitation regions reaches a maximum of 8.1 × 10 −16 cm 2 at the incident energy of 13 eV.

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Section: B Electronic Scattering Cross Sectionsmentioning

confidence: 99%

Absolute cross sections for electronic excitations of cytosine by low energy electron impact

Bazin

Michaud

Sanche

2010

The Journal of Chemical Physics

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“…The experimental value for w is 26.4 eV [13] and, for a gas mixture of Ar + 10% CH4, F is equal to 0.19 [17]. Figs.…”

Section: ) Resultsmentioning

confidence: 99%

“…Usually, the number n i of secondaries is calculated as Ki/~o, where ~o is the mean work to create an electron-ion pair. Its value, 26.4 eV [13], larger than lo, takes already into account the inefficient losses by excitation impacts. Division by w0 has been used in the ELD model for K i >1 1000 eV.…”

Section: Simulation In Terms Of Number Of Electrons Locally Depositedmentioning

confidence: 99%

Simulation of the measurement by primary cluster counting of the energy lost by a relativistic ionizing particle in argon

Lapique

Piuz

1980

Nuclear Instruments and Methods

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Energy loss of charged particles in a gas has been estimated by a computer simulation technique with a view of studying primary cluster counting as a mean of the particle identification. Primary electron yield and secondary multiplication have been estimated through a detailed calculation of the atomic processes. Results are presented for pure argon in terms of cluster size distributions and relativistic rise of the number of clusters: the latter reaches a plateau at a 3' of 200 and of level of 1.32 times minimum ionization. Limitations to detector resolution due to electronic dead time and longitudinal diffusion of the electrons drifting in the gas are presented. Such limitations are introduced in a comparison between the performance in particle separation of detectors based on energy loss, making use of pulse height measurement or cluster counting.

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“…From Ref. 28, it is seen that the electron impact ionization cross section for electron energies expected during the primary processes of ionization varies roughly inversely with the square root of the energy. Using this as a basis, the value of b was taken as b = k/1", where E is the 3 …”

Section: Variation Fraction Recombined With Particle Energymentioning

confidence: 99%

“…Over the next 10~1 2 sec the electrons produce between 0 and 10 further free electrons each. At this point the electrons should be characteristically confined to a radius b = 1O~4 cm, based on an electron scattering ionization mean free path of about 10~5 cm 28 .…”

Section: II Modeling Considerationsmentioning

confidence: 99%