HIGH-RESOLUTION PROTON ENERGY-LOSS SPECTROSCOPY OF THE HIGH OVERTONE VIBRATIONS IN CF4

Proton energy loss spectroscopy (PELS) has been used to investigate th e very high overtone states of the v(3) mode in CF4. With a new scatte ring apparatus, which is described here in detail, it has been possibl e to directly measure the energy levels of the dominantly excited v(3) mode up to its 14th overtone with an energy resolution of delta E = 1 0 - 15 meV, corresponding to 80-120 cm(-1). The data are interpreted u sing the Hecht vibrational Hamiltonian which predicts the tenser split ting of the v(3) mode energy levels into sublevel bands. By adjusting the values of the anharmonicity parameters X(33), G(33), and T-33, pre viously determined by IR spectroscopy and introducing a second-order a nharmonicity parameter X(333), it was possible to fit the v(3) mode en ergy levels to the measured energy loss distributions. A model based o n 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 inclu ding contributions from combinations with the v(1) and v(4) mode for c omparison with the experimental energy loss spectra. The influence of all relevant parameters on the simulated data is analyzed in detail. ( C) 1995 American Institute of Physics.