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Electron impact spectra of silane and germane have been recorded using electrons of 200 eV incidence at scattering angles of ∼2°–9°. The range of energy losses covers the entire region of single electron excitation from the valence shell. In the bound state spectrum evidence is presented supporting the existence of two valence transitions in addition to anticipated s, p, and d Rydberg transitions. The 9° spectra reveal much structural detail in the ∼4 eV energy range preceding the 2A1 ion state. The most prominent band consists of a superposition of an optically allowed valence excitation and a symmetry forbidden Rydberg transition. The remaining peaks may be members of vibrational progressions belonging to either [d(t2), a1], [p, a1] ← (a1)2 dipole allowed or [d(e), a1], [s,a1] ← (a1)2 dipole forbidden channels. Of these two possibilities the evidence presented here favors the latter choice. [ABSTRACT FROM AUTHOR]

We have examined the electronic structure of HgCl2 and HgBr2 from 5 to 14 eV by high resolution electron energy loss spectroscopy. Our measurements include the near-UV region which has not been examined by any previous technique and which is found to be rich in Rydberg states. In particular, in each molecule we identify members of two optically allowed Rydberg series and one forbidden series with electronic structues σ2gσ2uπ4uπ3g [npπu, npσu, and ndπg, or (n+1)sσg] which converge to the 2∏g ground ionic state. In addition, other structures which form the dominant energy loss mechanisms in our spectra are identified as arising from optically allowed Rydberg states associated with the excited ionic states 2Πu, 2Σu, and 2Σg. Measurements at energy loss below 9 eV confirm previous valence states observed in photoabsorbtion and suggest the existence of two new valence states in each molecule. Angular measurements facilitate identification of many of the newly observed structures in our electron-energy loss spectra. [ABSTRACT FROM AUTHOR]

Proton energy loss spectroscopy (PELS) has been used to investigate the very high overtone states of the ν3 mode in CF4. With a new scattering apparatus, which is described here in detail, it has been possible to directly measure the energy levels of the dominantly excited ν3 mode up to its 14th overtone with an energy resolution of δE=10–15 meV, corresponding to 80–120 cm-1. The data are interpreted using the Hecht vibrational Hamiltonian which predicts the tensor splitting of the ν3 mode energy levels into sublevel bands. By adjusting the values of the anharmonicity parameters X33, G33, and T33, previously determined by IR spectroscopy and introducing a second-order anharmonicity parameter X333, it was possible to fit the ν3 mode energy levels to the measured energy loss distributions. A model based on the earlier theoretical work of Levene and Perry [H. B. Levene and D. Perry, J. Chem. Phys. 84, 4385 (1986)] for the proton–CF4 scattering process is extended to allow the simulation of complete spectra including contributions from combinations with the ν1 and ν4 mode for comparison with the experimental energy loss spectra. The influence of all relevant parameters on the simulated data is analyzed in detail. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Energy loss distributions of He+ ions after collisions with HF molecules in a secondary beam at laboratory collision energies in the range 25–50 eV show a regular structure indicating rotational excitation up to ΔJ=35 with no clear evidence for vibrational excitation. The observed propensity for large ΔJ transitions decreases with increasing collision energy but increases with increase in scattering angle. Three dimensional quasiclassical trajectory calculations using a potential energy surface based on the He+–Ne interaction at short range and a damped long range ion–dipole (quadrupole) interaction reproduce all the essential features of the experimental results. [ABSTRACT FROM AUTHOR]