Photoelectron spectra of lodobenzenes

Abstract

The photoelectron spectra of iodobenzene and 1,2-, 1.3-, and 1.4-di-iodobenzene have been recorded by using He1 excitation. The electronic structure of these compounds is discussed in terms of a simple model of interaction between known orbitals of the composite parts, i.e. the moJecular orbitals of benzene and the 5p atomic orbitals of iodine, taking their energy and symmetry but no spin-orbit coupling into account. The assignment is simplified by the characteristic shapes of several systems, which. holds especially for the lone-pair electrons on iodine. Orbital sequences are given down to ionisation energies of 17 eV. Assignments are supported by comparison with the photoelectron spectra di-iodo-benzene.THE effect of substituents on the x-electron levels in substituted benzenes has been the subject of a number of investigations. Turner and his co-workers have shown the effect of substituents lifting the degeneracy of the elg n-orbitals of benzene and discussed it in terms of x-electron perturbation by inductive and mesomeric effects. They also discussed in general terms the effect of multiple substitution (1,2-, 1,3-, 1,4-, and perfluorosubstitution) and the characteristics of systems associated with lone-pair electrons of substituents. Most of their conclusions are still valid. However, the progress in theoretical (computational) and instrumental methods (instruments with better resolution) made it of interest to study the substituted benzenes systematically in t ?n leave from the Ruder BoSkovi6 Institute, and the Faculty 1 A

Vacuum–ultraviolet absorption and fluorescence spectroscopy of CF2H2, CF2Cl2, and CF2Br2 in the range 8–22 eV

“…6 is 261.5 cm -1 . 29 The features in the absorption spectrum have been assigned (Table IV), using vertical ionisation energies taken from Cvitas et al 24 The quantum defects obtained are generally in good agreement with those determined for either isolated chlorine (ns = 2.01, np = 1.57, nd = 0.09) or fluorine atoms (ns = 1.20, np = 0.75, nd = 0.003). 37 Care has been taken to ensure that the quantum defect determined for a particular orbital reflects the character of that orbital.…”

“…Many groups have measured He I and He II photoelectron spectra. [20][21][22][23][24][25][26][27][28] Selected values are listed in Table I. The energies of the key dissociation channels of CF 2 X 2 (X= H,Cl,Br) are also listed in Table I. The ground state energies were generally calculated from enthalpies of formation at 0 K given in the JANAF tables.…”

Vacuum-UV negative photoion spectroscopy of CF3Cl, CF3Br, and CF3I

“…The evidence for this property is best observed from photoelectron spectroscopy, where HeI, HeII and threshold photoelectron (TPE) spectra have been reported for CF 3 Cl, CF 3 Br and CF 3 I. [6][7][8][9][10][11] Bands observed in the spectra from ionization of an X lone pair or a C-X bonding electron shift to lower energy as X gets larger. However, bands observed from ionization of an F lone pair or a C-F bonding electron are very similar in energy for CF 3 Cl, CF 3 Br and CF 3 I. Absorption data on CF 3 Cl have been well studied by photoabsorption spectroscopy 12,13 and electron energy loss spectroscopy (EELS).…”

Two Studies in Gas-Phase Ion Spectroscopy

“…The fact that features are observed in both spectra at similar energies suggests these do indeed represent competing decay channels from the same Rydberg states. Vertical ionisation energies for CF 3 Cl +D2 E,Ẽ 2 A 1 ,F 2 E andG 2 A 1 are 17.71, 20.20, 21.20 and 23.80 eV, respectively [53]. The features in the spectra at 17.6, 19.7 and 20.9 eV are assigned to high-lying Rydberg states (n [ 5) converging on theD,Ẽ andF ionisation limits, respectively.…”

“…The values for k c given in this work use the model formulated by Chesnavich et al [51], and further modified by Su and Chesnavich [52][53][54]. It assumes the potential energy interaction between the reactant ion and molecule takes the form:…”