The ionic states of iodobenzene studied by photoionization andab initioconfiguration interaction and DFT computations (original) (raw)
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The Journal of Chemical Physics, 2015
New valence electron photoelectron spectra of iodobenzene obtained using synchrotron radiation have been recorded. Ionization energies (IE) determined using multiconfiguration SCF calculations (MCSCF) procedures confirmed the adiabatic IE order as: X 2 B 1 < A 2 A 2 < B 2 B 2 < C 2 B 1. Although it is convenient to retain C 2v labelling, there is evidence that minor distortion to C S symmetry occurs at the MCSCF level for the C state. The fifth ionization process shown to be D 2 A 1 , exhibits dissociation to C 6 H 5 + + I, both in the experimental and theoretical studies. The calculated Franck-Condon vibrational spectral envelopes, including hot band contributions, for the first four ionic states reproduce the observed peak positions and intensities with reasonable accuracy. In order to simulate the
Journal of Chemical Physics, 2015
New photoelectron, ultraviolet (UV), and vacuum UV (VUV) spectra have been obtained for bromobenzene by synchrotron study with higher sensitivity and resolution than previous work. This, together with use of ab initio calculations with both configuration interaction and time dependent density functional theoretical methods, has led to major advances in interpretation. The VUV spectrum has led to identification of a considerable number of Rydberg states for the first time. The Franck-Condon (FC) analyses including both hot and cold bands lead to identification of the vibrational structure of both ionic and electronically excited states including two Rydberg states. The UV onset has been interpreted in some detail, and an interpretation based on the superposition of FC and Herzberg-Teller contributions has been performed. In a similar way, the 6 eV absorption band which is poorly resolved is analysed in terms of the presence of two ππ* states of 1 A 1 (higher oscillator strength) and 1 B 2 (lower oscillator strength) symmetries, respectively. The detailed analysis of the vibrational structure of the 2 2 B 1 ionic state is particularly challenging, and the best interpretation is based on equation-of-motion-coupled cluster with singles and doubles computations. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene. The equilibrium structures of the 3b 1 3s and 6b 2 3s (valence shell numbering) Rydberg states have been obtained and compared with the corresponding ionic limit structures.
Journal of the American Chemical Society, 1997
The results of ab initio calculations on 1,3,5-trimethylenebenzene (1) and its negative ion (1 -) are presented. Geometries were optimized at the CASSCF/6-31G* and CASSCF/6-31+G* levels. Single-point calculations were performed using second-order perturbation and multireference configuration interaction (MR-CI) methods, in order to include the effects of dynamic correlation between the σ and π electrons. The ground state of 1 is predicted to be the high spin 4 A 1 ′′ state, which has D 3h symmetry. The lowest energy excited state is 2 E′′ in D 3h symmetry and is thus subject to first-order Jahn-Teller distortions to geometries of lower symmetry. The C 2V geometries of the two Jahn-Teller distorted components of 2 E′′, 2 B 1 and 2 A 2 , have been optimized and are found to have nearly the same energies. After correction for zero-point energy differences, the adiabatic energy separation between the lowest C 2V doublet and the D 3h quartet ground state of 1 is computed to be 14 ( 1 kcal/mol. The ground state of 1 -is predicted to be 3 E′ in D 3h symmetry. Molecular distortion to C 2V symmetry stabilizes the 3 B 2 component of 3 E′ via not only first-but also second-order Jahn-Teller effects. Consequently, the 3 B 2 component of 3 E′, at its optimized geometry, is calculated to be lower in energy by ca. 1.5 kcal/mol than the 3 A 1 component at its optimized geometry. The lowest singlet excited state of 1 -is 1 A 1 ′ in D 3h symmetry, which is predicted to undergo second-order Jahn-Teller distortions, at least at the CASSCF level of theory. The resulting state, 1 A 1 in C 2V symmetry, is calculated to be 4-6 kcal/mol above the 3 B 2 ground state but slightly below a 3 A 2 ′ excited state of D 3h symmetry. In contrast to CASSCF and MR-CI, UB3LYP/6-31+G* calculations predict 3 A 2 ′ to be the ground state of 1 -, slightly below either component of the Jahn-Teller distorted 3 E′ state. The UB3LYP calculations afford an estimate of 21-22 kcal/mol for the electron affinity of 1 and provide vibrational frequencies for the 4 A 1 ′′ state. On the basis of computational results for 1 and 1 -, the most important features of the photoelectron spectrum of 1 -are predicted.
Electronic structure of haloalkanes: a high resolution photoelectron spectroscopic study
Journal of Molecular Structure, 1993
High resolution He(I) photoelectron spectra @'ES) of a number of bromo-and iodoalkanes have been measured. Linear relationships between ionization energies (Ei) and l/n (where n is the number of carbon atoms in the chain) describe the trends reasonably well if n = 1 is excluded for dihaloalkanes. This property (i.e. line slopes) when joined with the alternation of halogen lone pair bandwidths within a given spin-orbit doublet, can be used to provide a fully empirical assignment of the four non-bonding orbital ionizations of dihaloalkanes. The interactions between the halogen lone pair orbitals and the alkane cr orbitals dominate in dihaloalkanes for which n 2 2, while through-space interaction is important only in dihalomethanes (n = 1). Vibrational fine structures were used to infer the existence of hyperconjugative effects.
European Journal of Mass Spectrometry, 2004
The dissociation onset for halogen atom loss was investigated for 2-iodo and 2-chloropropane ions using a newly developed threshold photoelectron photoion coincidence (TPEPICO) technique that suppresses the effects of hot electrons. This study was undertaken in order to resolve current discrepancies concerning these onsets in the literature. The 0 K dissociation thresholds were determined to be 9.818 ± 0.010 and 11.036 ± 0.010 eV for 2-C3H7I and 2-C3H7Cl, respectively. These numbers agree quite well with photoionization and a mass analyzed threshold ionization (MATI) study, but are significantly lower than onsets measured by the much higher resolution pulsed field ionization PEPICO method. The derived C3H7+ heat of formation at 298 K is 803.9 ± 1.5 kJ mol−1, and a more precise value for the 298 K 2-iodopropane heat of formation is −40.8 ± 1.3 kJ mol−1. The derived proton affinity of propene is 746.1 kJ mol−1. We have also performed a high-level ab initio calculation on the 0 K disso...
Physical Chemistry Chemical Physics, 2002
Vibrationally resolved C1s photoelectron spectra of benzene and d 6 -benzene have been recorded using monochromated synchrotron radiation at photon energies of 330 eV. The spectrum of normal benzene displays considerable vibrational structure. Particularly noteworthy is the strong excitation of a combined CCH-bending and CC-stretching mode which splits the main peak into two well-defined maxima. In d 6 -benzene, the vibrational energy levels are less well separated and the vibrational structure is reduced to strong asymmetry of the main peak and a broad tail extending toward higher ionization energy. The recorded spectra are analyzed using first-principle and curve-fitting procedures. A theoretical model that allows for incomplete localization of the core hole, results in very good fits to the experimental spectra of both benzene and d 6 -benzene.
Photoionization of the iodine 3d, 4s, and 4p orbitals in methyl iodide
The Journal of chemical physics, 2018
Ionization of the I 3d, 4s, and 4p orbitals in methyl iodide (CHI) has been studied by using synchrotron radiation to measure the total ion yield and by recording photoelectron spectra with linearly polarized radiation in two polarization orientations. The complete photoelectron spectrum of CHI has been recorded at several photon energies, and bands due to the C 1s, I 3d, 4s, 4p, and 4d atomic-like orbitals, as well as the molecular orbitals, have been observed and assigned. In the vicinity of the I 3d and 3d ionization thresholds at 626.8 and 638.3 eV, respectively, the ion yield displays weak structure in the pre-edge region due to transitions into valence or Rydberg states, and, at higher energies, a shoulder and a broad maximum attributed to the I 3d → f and the I 3d → f shape resonances, respectively. The absorption spectrum calculated using time-dependent density functional theory, within the Tamm-Dancoff approximation, has allowed assignments to be proposed for the valence an...