Molecular Spectroscopy by Electron Scattering

We have investigated the low-energy (0-10 eV) electron attachment on C 60 and C 70 , using an improved energy resolution close to zero incident energy (0.030-0.060 eV). We have found evidence of a zero-energy attachment process (within 0.030 eV), for both C 60 and C 70 , indicating that a s-wave capture process is present at low energy for these two molecules. For C 60 , although in contrast with symmetry arguments, and with previous free-electron attachment experiments, this result is in full agreement with the conclusions presented by several groups, using the Rydberg atom energy transfer technique to investigate the low-energy attachment in these systems. Energy positions of several resonant states, appearing between 0.5 and 5 eV in the ion yield versus electron energy spectrum, are clearly established in C 60 and C 70 , and assignments are discussed. Lifetime measurements are reported for the fullerene anions. In the incident energy range 7-11 eV the lifetime τ of C − 60 was found to vary from 500 to 45 µs, respectively, in agreement with previous measurements. The thermionic model for C − 60 detachment does not seem to describe the values obtained, and their observed variation in this energy range. The lifetime of C − 70 is longer and could not be measured precisely with our time-of-flight conditions. An estimation of τ ≈ 700 µs has been made at E i = 11 eV. Below E i = 7 eV the lifetime of C − 60 was larger than 700 µs and could not be measured precisely.

Section: Anion Yields Versus Electron Energymentioning

confidence: 99%

Low-energy electron attachment to fullerenes and in the gas phase

Elhamidi

Pommier

Abouaf

1997

“…Obtaining information on resonances from elastic DCS or integrated cross sections in the range of energies considered in this paper, 1.5-100 eV, is difficult. Fortunately, direct scattering in vibrational excitation (the constant term in the Breit-Wigner formula, Hall and Read (1984)) is small and the resonance may then appear as a Lorentzian peak in plots of DCS versus impact energy. When the extra electron is temporarily trapped in a potential valley created by the combination of an attractive potential and the centrifugal potential, the resonance is called a shape resonance and usually short-lived, i.e.…”

Section: Vibrationally Inelastic Cross Sectionsmentioning

confidence: 99%

Vibrationally inelastic and elastic cross sections for collisions

Boesten

Tachibana

Nakano

et al. 1996

Absolute elastic cross sections for electron impact on nitrogen trifluoride have been recorded for impact energies from 1.5 to 100 eV and scattering angles from to . Because of the small dipole moment, estimates of the integrated and momentum-transfer cross sections were obtained by extrapolation of the angular range with the help of a modified phase-shift program and subsequent numerical integration under the fits. Vibrational excitation function measurements show a 2 eV wide resonance at 3 eV impact energy. Vibrational loss spectra were measured near this resonance and resolved into their vibrational components and . From the angular behaviour of these fundamental modes, the resonance can be assigned to a temporary trapping of the impinging electron in the antibonding orbital of irreducible species `e', the LUMO orbit.

“…Resonance excitation of excited electronic states of H 2 typically takes place between 11 and 16 eV via the formation of a negative molecular anion, which subsequently rapidly (0.1-1 fs) autoionizes to an excited electronic state of the neutral species. The electronic resonance excitation of H 2 by electrons has been reported in the experimental work of Kuyatt et al (1966), Weingartshofer et al (1970Weingartshofer et al ( , 1975, Comer and Read (1971), Golden (1971), Sanche and Schulz (1972), Elston et al (1974), McGowan et al (1974), Schowengerdt and Golden (1975), Böse and Linder (1979) and have been extensively reviewed by Schulz (1973), and Hall and Read (1984).…”

Section: Introductionmentioning

confidence: 99%

Electron impact excitation of H₂: resonance excitation of B¹ _u(J_j 2,v_j 0) and effective excitation function of EF¹ _g

Liu

Shemansky

Abgrall

et al. 2003

The electron impact emission function of the P(3) branch for the (0, 4) band of the H2 B 1Σ u+–X 1Σ g+ band system has been measured from threshold to 1800 eV. The emission function exhibits structure indicating strong contributions from both resonance and non-resonance excitation. The non-resonance component contains direct and cascade contributions. A combination of experimental and theoretical considerations permits separation of resonance, dipole-allowed direct, dipole-allowed indirect, and dipole-forbidden excitation components for the Jj = 2, vj = 0 level of the B 1Σ u+ state. An effective excitation function for the EF 1Σ g+–X 1Σ g+ band system has been obtained from a nonlinear least-squares analysis of the dipole-forbidden component of the B 1Σ u+ state emission function. The absolute value of EF 1Σ g+–X 1Σ g+ cross section is established on the basis of earlier experimental results of Liu et al 1995 Astrophys. J. Suppl. 101 375–99 and 2002 Astrophys J. Suppl. 138 229–45 and Abgrall et al 1997 Astrophys. J. 481 557–66 and 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3813–38. A near-threshold apparent resonance excitation cross section of (8.1 ± 3.2) × 10−18 cm2 is obtained for the B 1Σ u+ (Jj = 2 and vj = 0). An EF 1Σ g+–X 1Σ g+ Born cross section has been calculated from the electronic form factor of Kolos et al 1982a J. Chem. Phys. 77 1335–44. Analysis shows that the Born asymptotic shape function of the EF 1Σ g+–X 1Σ g+ band system starts at ∼400 eV, a significantly higher energy than previously expected. The excitation function is especially important for interpreting outer planet atmospheric dayglow and auroral activity and can be used to infer energy deposition and heating rates.