Lowest Energy Electronic Absorption Research Articles

Electronic band-shape calculations in ammonia

The vibronic nature of the lowest energy electronic absorption and of the lowest energy photoelectron spectrum of NH3 are investigated theoretically. Two-dimensional Franck–Condon factor calculations are performed and theoretical spectra are constructed including the effect of vibronic linewidth. The comparison of the experimental with theoretical spectra, computed under various assumptions, leads to several conclusions. The conspicuous continuum underlying the ?←? transition is seen to arise from the overlapping tails of vibronic line shapes. There is no need to attribute the continuum to a second electronic transition. The ν1, N–H stretching mode, is excited in both the electronic absorption and photoelectron spectrum. The ? state of NH3 may be able to support two quanta of ν1. The planar NH3+ ion has a N–H bond longer than in the ground state NH3 by about 0.06 Å.

A high resolution, low energy electrostatic analyser for rocket payloads

The scientific constraints on the measurement of suprathermal electron fluxes in the 1–500 eV energy range in the auroral zone are discussed. These constraints are used to define the characteristics of an electrostatic analyser to measure such fluxes. The design and calibration of such an instrument are described. The application of the instrument to measure details of atmospheric absorption of low energy electrons by utilizing its high energy resolution, and the application to measure detailed variations of spectrum and pitch angle distribution by utilizing its high sensitivity are discussed with reference to a number of rocket flights made from the northern auroral zone.

Oxygen-l7 nuclear magnetic resonance. Part I. Oxygen–nitrogen groupings

Oxygen-l7 shifts are reported for N2O3, N2O4, MeONO, Me2NNO, NO2+, and NOCl, with 17O in natural abundance. These are compared with literature values of 17O shifts in other oxygen–nitrogen groupings, and with the corresponding nitrogen shifts. The shifts of adjacent oxygen and nitrogen in the same chromophore are roughly in the proportion of their respective values of 〈r–3〉, which gives the dependence of the paramagnetic shielding term (σp) on the radius of the 2p orbitals. The oxygen resonances tend to move downfield as the lowest-energy electronic absorption moves to longer wavelengths, but the scatter is large. The oxygen shielding in XNO and XNO2 compounds (as in RCOX) reflects the conjugative effect of the substituent X. This contrasts with the nitrogen shielding, in which inductive effects are relatively more important. Inductive effects may however be among those responsible for oxygen shift relationships, in certain sets of compound, that differ from the overall trends. The relative importance of the orbital terms that contribute to σp is compared for oxygen and nitrogen in these groupings.

The intensities of low-energy electronic absorption transitions of some carbonyls and thiocarbonyls

The intensities of low-energy electronic transitions for some carbonyls and thiocarbonyls have been calculated from CNDO wavefunctions. Quite good agreement with experimental results has been obtained, where the latter are available. A satisfactory approximation for calculating intensities employs only one-center integrals. From the calculated trends in oscillator strengths, the absorption of thiophosgene at 4.46 eV can be identified as the π→π* 1A 1←X̃ 1A 1 system. Another, very weak, system of thiophosgene at ≈ 3.9 eV is tentatively assigned to an n→π* 1A 1 ← X̃ 1 A 1 transition, with the n orbital localized on the chlorine atoms.

Empirical relations for absorption of low energy positrons and electrons in metals

The absorption of low energy positrons and electrons in metals is found to be Z-dependent and obeys an empirical relation of the form t = K exp (m Z 1 3 ) . Experimental results are used to obtain values of m for positrons and electrons.

Observation de plaquettes de pyrographite par diffraction des électrons lents et des rayons X

Low energy electron diffraction patterns obtained from pyrographite samples correspond to a two-dimensional lattice. The same samples examined with X-rays exhibit patterns due to the three-dimensional structure. This difference gives proof of the strong absorption of low energy electrons by matter. In all cases a fibrous texture with axis c is brought to light.

Relations entre la symétrie des diagrammes de diffraction des électrons lents et celle du cristal

The very strong absorption of low energy electrons by matter has some consequences on the symmetry of diffraction patterns. The symmetry of a pattern is that of one or several structural planes according to the depth reached by the electrons. It may differ from the symmetry of the crystal unit cell. When the symmetry of the crystal is lower than that of the structural planes, the symmetry of the pattern corresponds to that of the diffracting medium whereas if the symmetry of the crystal is higher than that of the structural planes, the symmetry of the pattern is lower than that of the diffracting medium.

Experiments with a Magnetic Lens Spectrometer, employing Post-focusing Acceleration: the L-Auger Lines of Thorium-active Deposit

A post-focusing electron accelerator has been developed to reduce the absorption of low-energy electrons by the Geiger counter window of a β-ray lens spectrometer. Its useful range is for β-rays having energies between 0 and 30 kev., and although, in general, for a portion of this range only partial transmission will be obtained, correction curves for the absorption can be accurately determined. In order to test the spectrometer, an investigation of the L-Auger lines of thorium-active deposit has been made. An identification of the lines has been attempted.