Interpretation Of Photoelectron Spectra Research Articles

Identification of singlet excited electronic states of toluidine isomers

The photoelectron and UV absorption spectra of para-, meta-, and ortho-toluidine in the gas phase are obtained. The photoelectron spectra in the energy region up to 15.5 eV are interpreted based on the B3LYP/6-311+G(d, p) calculations. Based on the TDDFT B3LYP/6-311+G(d, p) calculations and taking into account the obtained interpretation of photoelectron spectra, the UV absorption bands are assigned to particular singlet transitions. For each transition, the electron configuration that makes the dominant contribution to the transition is determined. It is shown that the transition energy for toluidine isomers depends on the energy gap between the corresponding occupied and unoccupied molecular orbitals. It is noted that this dependence is similar for different benzene derivatives.

High-Resolution Photoelectron Spectroscopy and ab initio Quantum Chemistry

The resolution that can be achieved by photoelectron spectroscopy has been continually improved over the past 50 years and is now sufficiently high for the rovibronic energy level structure of polyatomic molecular cations to be measured accurately. Ionisation potentials, molecular constants, and in some cases the potential energy surfaces of both the neutral and the ionic states connected by the photoionising transitions can be extracted from photoelectron spectra and used to test ab initio quantum chemical calculations. Ab initio quantum chemistry represents an essential tool to assign photoelectron spectra and to rationalise the experimental observations. Because either the neutral or the ionised species, or even both, connected by a photoionising transition possesses at least one unpaired electron, photoelectron spectroscopy represents a very convenient method to study openshell molecules. Unfortunately, much fewer highly accurate ab initio quantum chemical calculations have been reported on open-shell than on closed-shell molecules, and such calculations would be desired to assist in the interpretation of photoelectron spectra. This contribution illustrates the fruitful interplay between ab initio quantum chemistry and photoelectron spectroscopy with examples chosen from our recent work on the photoelectron spectra of the rare gas dimers and of small polyatomic hydrides and hydrocarbons. It also briefly reviews the experimental progress that makes it possible today to measure the fine and hyperfine structure in molecular ions by experimental techniques closely related to photoelectron spectroscopy.

Interpretation of photoelectron spectra in terms of the semi-empirical AM1 method

Equilibrium torsional angles of 2-phenylpyrroles and their radical cations in the ground and ionized states have been estimated using UV photoelectron and electron spectroscopies, respectively, in combination with AM1 quantum-chemical calculations. A theoretical study of the internal rotation potential by means of the total energy partitioning approach has led to the following conclusions. a) In the case of molecules and radical cations of biphenyl and its heteroanalogs, the tendency to adopt a planar conformation (V2 barrier) is determined, in the first place, by the contribution of the two-center resonance component of the interannular bond energy. b) Non-valence interactions are vital for the stabilization of the gauche conformation. Their effect on theV4 barrier of biphenyls is stronger than that observed for 2-phenylpyrroles.

Chemistry of excited states. XI. Interpretation of photoelectron spectra by final state single CI method within semiempirical formalisms

AbstractThe single excited doublet states of some small molecule cations calculated by CI method in the framework of semiempirical CNDO and INDO models are correlated with the photoelectron spectra of the parent molecules. The purity of the Koopmans transitions is used to discuss the one‐particle interpretation of photoelectron bands by comparison with nonempirical many‐body calculations. Furthermore, empirical relations are applied with respect to the evaluation of shake‐up energies.

Molecular orbital calculations based on linear combinations of fragment orbitals

A semiempirical MO method based on localized fragment orbitals has been developed, which is particularly suited for the construction of orbital correlation diagrams for the discussion of the electronic structure of complex molecules in terms of fragments and their interactions. The method allows for the inclusion of experimental ionization potentials and electron affinities of the fragments within the calculation of the Fock matrix elements and may thus form the basis of an interpretation of photoelectron spectra, comparable to the interpretation of UV spectra by means of the MIM method of Longuet-Higgins and Murrell. Several levels of approximation are discussed using the acrolein molecule as an example.

Use of spin-orbit coupling in the interpretation of photoelectron spectra. I. Application to substituted rhenium pentacarbonyls

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUse of spin-orbit coupling in the interpretation of photoelectron spectra. I. Application to substituted rhenium pentacarbonylsMichael B. HallCite this: J. Am. Chem. Soc. 1975, 97, 8, 2057–2065Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://doi.org/10.1021/ja00841a011RIGHTS & PERMISSIONSArticle Views251Altmetric-Citations56LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Computational study of vertical ionization potentials using the ΔINDO + FOCI method

The computational procedure devised by Segal has been employed to estimate ionization potentials by energy differences. In order to obtain similar accuracy with both open- and closed-shell species, a first-order configuration interaction (FOCI) calculation is performed after the SCF procedure for the open-shell system. In this work, the SCF scheme is based on the INDO approximation. In general, these ΔINDO + FOCI computations provide adequate interpretations of photo-electron spectra. For closed-shell parent molecules, comparison of the ionization potentials calculated by Koopmans' Theorem and those by the ΔSCF + FOCI method leads to an estimate of the electronic reorganization taking place on ionization. The results of the present calculations indicate that electronic rcargauization is insufficient to affect the ordering of the first few cationic states predicted by Koopmans' Theorem. The major exception to this occurs for the molecules H2CO and F2CO.

A semi-empirical method for the calculation of spin—orbit splitting in degenerate electronic states of linear polyatomic molecules

A semiempirical method for the calculation of spin—orbit coupling constants in linear polyatomic molecules is discussed. The method uses the readily available output from a CNDO/2 calculation and a set of effective atomic coupling constants obtained from observed spectroscopic data on atoms. Two procedures for obtaining the spin—orbit splitting are discussed: one based on a closed shell CNDO/2 calculation and one based on an open shell calculation. The average error for the molecules studied was 6.8% and 7.7% for the two procedures used in the calculations, the easier closed shell procedure giving the lower percentage error. It should be noted that the largest errors occurred in the case of diatomic molecules where the error would be expected to be the greatest. Thus, the average error involved in the values of the spin—orbit splitting for polyatomic molecules is much less than 3.7% for the closed shell procedure. The method used appears to be extendable to non-linear molecules in which the only atoms off the principle symmetry axis of the molecules are hydrogen. The method should be useful in the interpretation of photoelectron spectra.

A semi-empirical method for the calculation of spin—orbit splitting in degenerate electronic states of linear polyatomic molecules

A semiempirical method for the calculation of spin—orbit coupling constants in linear polyatomic molecules is discussed. The method uses the readily available output from a CNDO/2 calculation and a set of effective atomic coupling constants obtained from observed spectroscopic data on atoms. Two procedures for obtaining the spin—orbit splitting are discussed: one based on a closed shell CNDO/2 calculation and one based on an open shell calculation. The average error for the molecules studied was 6.8% and 7.7% for the two procedures used in the calculations, the easier closed shell procedure giving the lower percentage error. It should be noted that the largest errors occurred in the case of diatomic molecules where the error would be expected to be the greatest. Thus, the average error involved in the values of the spin—orbit splitting for polyatomic molecules is much less than 3.7% for the closed shell procedure. The method used appears to be extendable to non-linear molecules in which the only atoms off the principle symmetry axis of the molecules are hydrogen. The method should be useful in the interpretation of photoelectron spectra.

Reply to the paper “The interpretation of photoelectron spectra, especially those of benzene and water” by A. D. Baker, C. R. Brundle and D. W. Turner

Reply to the paper “The interpretation of photoelectron spectra, especially those of benzene and water” by A. D. Baker, C. R. Brundle and D. W. Turner

The use of Koopmans' Theorem in the interpretation of photoelectron spectra

Theoreticians are aware of the dangers inherent in the use of Koopmans' Theorem to equate calculated molecular orbital energies with observed ionisation potentials. Experimentalists, however, still use the theorem in the interpretation of results, particularly in photoelectron spectroscopy. This paper reviews the assumptions involved and indicates how calculations can be used safely.

The interpretation of photoelectron spectra — especially those of benzene and water

Recent interpretations of photoelectron spectra of benzene and water in terms of vanishing cross-sections for ionisation of certain σ-orbitals by He 584 Å radiation are criticized. It is shown that the evidence that was cited in support of this concept was inconclusive and that alternative explanations exist. The evidence is shown to point to the use of Helium 584 Å (or higher-energy) radiation as a significant factor in avoiding anomalous spectral features. The discrepancies between theoretical calculations of molecular orbital structure and the results of He 584 Å photoelectron spectroscopy may be ascribable to deviations from the Koopmans' Theorem basis.