Valence and Rydberg states of ethyl iodide by electron energy loss spectroscopy

Abstract

The energy scheme of ethyl iodide has been studied by excitation of the valence and Rydberg states lying in the near u v and uv (3-10eV) by electron impact and the angularly resolved electron energy loss spectroscopy. The lowest energy valence triplet states have been identified in the 3-5.5 eV region with a maximum of transition probability around 4.3 eV and at 4.78 eV respectively. Additional valence singlet and/or triplet states have been suggested to be located between 5 and 6 eV. For the Rydberg series, several electronic states contribute to the lowest energy terms ofthe Rydberg bands. The differential cross sections for the B, C and D Rydberg bands have been measured and confirm that each state within the electronic multiplet in each,band has a differential cross section different from that of the other. In addition excitation of the A, states is very likely responsible of a minimum in the D/C and D/B differential cross section ratios. In addition the first terms of two new nd series converging to each spin-orbit component of the ionic ground state have been reported. Vibrationai levels of the E(1) states which are the most intense in pseudo-optical conditions have been partly resolved for the first member of the ns, fzp and nd series.

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

“…The present results will be discussed in the approximate C 3v symmetry, which is that of CH 3 I, as previously done. 10,11,14 This means physically that the methyl group only slightly perturbs the local symmetry around the iodine atom and leads us to neglect the influence of this group on the spectroscopy of the ion and of the Rydberg states.…”

“…͑1͒ The peak energy position, E n , must fit the Rydberg formula: E n ϭE i ϪR/(nϪ␦) 2 , where E i is the ionization energy ͑E i ϭ9.341 eV for 2 E 3/2 and E i ϭ9.927 eV for 2 E 1/2 ͒, n is the principal quantum number of the Rydberg orbital of energy E n , R is one Rydberg, and ␦ is the quantum defect. For iodine: 3.9Ͻ␦Ͻ4.2 for ns, 9,14,34 3.5Ͻ␦Ͻ3.9 for np, 14,34 and 1.8Ͻ␦Ͻ2.7 for nd. 8,9,14,34 ͑2͒ The 0.586 eV splitting of the ionic components.…”

“…͑3͒ The intensity ratio of the bands. 35 Table V [8][9][10]14 gives the energy values of the photoabsorption features, the assignments to members of Rydberg series, and the excitation energies reported in previous work.…”

“…This part of the spectrum has been interpreted as arising from the transition of a lone-pair iodine electron to the Rydberg orbital 6sa 1 . [9][10][11][12]14 The 0-0 transitions to the E(1) and the E(3) states have been assigned to peaks 3 and 17, respectively, these being the most intense in this region; also, their energy separation, 0.56 eV, is close to the spin-orbit splitting of the ion. The vibrational structure built on E(1) ͑peak 3͒ is interpreted by comparison with the PES spectrum.…”

“…Finally, the electronic excitation spectrum of ethyl iodide has been explored by electron impact, the electron energy loss spectrum covering a broader energy range than the photoabsorption spectra but with a lower resolution; this identified a new Rydberg series at high energy and confirmed the presence of the 3 Q 1 (E) valence state at 4.1 eV. 14 In this paper, we report new data on the electronic spectroscopy and absorption cross sections of ethyl iodide in the 4 eV-14.2 eV region. We have made use of two experimental methods: ͑1͒ high resolution VUV photoabsorption using synchrotron radiation to provide absolute cross sections; and ͑2͒ electron energy loss spectroscopy in dipolar excitation conditions to provide relative excitation cross sections at higher excitation energies.…”