Vibrational and Vibronic Structure in the Valence Electron Spectra of CH₃X Molecules (X=F, Cl, Br, I, OH)

Abstract

Valence electron spectra of the methyl halides and of methyl alcohol have been induced by means of the HeI resonance radiation at 21.22 eV. A large number of new vibrational bands are reported. The observation of these was facilitated by a high instrumental resolving power and fast data acquisition. In most cases the new bands are observed in 1 A 1→2 E transitions but also the electron band of the 1 A 1→2 A 1 transition of CH3I exhibits extensive progressions of closely spaced vibrational bands not previously reported. The vibrational structure of the 1 A 1→2 E transitions is affected by vibronic coupling. The structure of the 2e electron band of CH3Cl probably reflects the operation of the Ham effect. Calculations of the band structure including spin-orbit coupling are performed according to a model which is briefly described.

The vacuum UV photoabsorption spectrum of methyl chloride (CH3Cl) and its perdeuterated isotopomer CD3Cl I. A Rydberg series analysis

“…Energy positions estimated from the dipole (e,e) cross-section curve as reported by Olney et al [18] and from the high energy photoabsorption curve published by Wu et al [16] are inserted in this table. The convergence limits listed in this table are those reported by Karlsson et al [22] and by Von Niessen et al [23] and obtained by the He(I) and He(II) resonance lines respectively. Question marks indicate uncertainty on the assignments of convergence limits [24].…”

“…Higher lying vertical ionization energies are located at 14.4 eV (3a 1 -1 ) and 16.0 eV (1e -1 ) [22]. With the He(II) resonance line at 30.4 nm, the ionization of the inner-valence orbitals is possible and vertical ionization energies are measured at 21.2 eV (2a 1 -1 ) and at 24.1 eV (1a 1 -1 ) [18,23].…”

“…The 1a 1 and 2a 1 correspond to the inner-valence molecular orbitals whereas the le, 3a 1 and 2e molecular orbitals have outer-valence character. The most accurate and well-resolved He(I) photoelectron spectrum [22] provides the adiabatic ionization energies at 11.289 ± 0.003 eV (2e -1 ), 13.8 eV (3a 1 -1 ) and at 15.4 eV (1e -1 ) successively. The lowest ionic state shows a 2 E 3/2 -2 E 1/2 spin-orbit splitting of 27 ± 6 meV (218 ± 48 cm -1 ) [22], with adiabatic ionization energies of 11.289 ± 0.003 and 11.316 ± 0.003 eV respectively.…”

“…The most accurate and well-resolved He(I) photoelectron spectrum [22] provides the adiabatic ionization energies at 11.289 ± 0.003 eV (2e -1 ), 13.8 eV (3a 1 -1 ) and at 15.4 eV (1e -1 ) successively. The lowest ionic state shows a 2 E 3/2 -2 E 1/2 spin-orbit splitting of 27 ± 6 meV (218 ± 48 cm -1 ) [22], with adiabatic ionization energies of 11.289 ± 0.003 and 11.316 ± 0.003 eV respectively. As will be discussed in the accompanying paper, the strength of the Jahn-Teller distortion is small compared to the spin-orbit coupling.…”

“…In the same figure the assignment of the main features to series of vibrationless Rydberg transitions has been inserted. The convergence limits are the ionization energy values reported by Karlsson et al [22] as measured by He(I) photoelectron spectroscopy. Fig.…”