Electronic excitation and oscillator strength of ethyl iodide by VUV photoabsorption and electron energy loss spectroscopy

A high resolution VUV photoabsorption spectrum of ethyl iodide has been rec orded between 4 and 10.2 eV (310-120 nm) using synchrotron radiation. The s pectrum consists of a broad structureless absorption band centered at 4.78 eV, followed by a region dominated by excitation of Rydberg states. A high resolution photoelectron spectrum (PES) of the lowest energy ionization ban d has been obtained and provides ionization energies necessary for identifi cation of related Rydberg-excited states. Also, analysis of the vibrational fine structure in the PES has allowed identification of the normal vibrati onal modes excited and their wave numbers in the ion. These, in turn, have been used in the assignment of the lowest energy photoabsorption bands aris ing from electron excitation into the 6s Rydberg orbital. An electron energ y loss spectrum has also been recorded from 5.8 to 14.2 eV, under electric- dipole conditions. It confirms the magnitude of the photoabsorption cross s ection values obtained using the synchrotron radiation and extends the diff erential and optical oscillator strength values up to 14.2 eV. (C) 1999 Ame rican Institute of Physics. [S0021-9606(99)01220-9].