Symmetry Breaking and Non‐Born‐Oppenheimer Effects in Radical Cations

The various electronic states in which molecules can exist are often considered to be independent. In this article we turn our attention to the limitations of this assumption, namely the interaction between different electronic states through the nuclear motion. This interaction can have several important consequences, two of which are discussed in some detail. One is a distortion of the molecular framework, leading to a lowering of the symmetry of a molecule in excited or ionic states compared to the neutral ground state. General aspects of this symmetry lowering are outlined and interpreted with the aid of typical examples. The other consequence considered is the ability of the nuclei to “jump” between different molecular potential energy surfaces (non-Born-Oppenheimer effects). The nature of this behavior is analyzed and it is argued that the “jumping” can be very fast and efficient, dominating completely the nuclear motion. To exemplify our general ideas we refer to the photoelectron spectra of ethylene and related compounds and demonstrate that they are governed by strong non-Born-Oppenheimer effects. It emerges that the Franck-Condon principle fails in the analysis of their vibronic structure.

[1]  L. Cederbaum,et al.  Strong nonadiabatic effects and conical intersections in molecular spectroscopy and unimolecular decay: C2H4+ , 1982 .

[2]  M. Pawlikowski,et al.  Vibronic analysis of circular dichroism spectra of dimeric systems. Chiral molecules consisting of two polyacene chromophores , 1982 .

[3]  K. Dressler,et al.  Multistate vibronic coupling between the excited 2Π states of the NO molecule , 1982 .

[4]  D. J. Bellville,et al.  Twisting in alkene ion radicals , 1982 .

[5]  G. Olbrich.  A Semi‐Empirical Investigation into the Trans‐Cis Photoisomerisation of Stilbene , 1982 .

[6]  K. Innes.  s‐tetrazine: Coupling of the S0 to the S1 electronic state by two out‐of‐plane b3u vibrations , 1982 .

[7]  J. Maier.  Open-shell organic cations: spectroscopic studies by means of their radiative decay in the gas phase , 1982 .

[8]  J. P. Maier.  Struktur und Relaxationsdynamik organischer Radikalkationen in der Gasphase, illustriert am Beispiel des 1,3‐Pentadiin‐Kations , 1981 .

[9]  J. Maier.  Structure and Decay of Gaseous Organic Radical Cations Studied by Their Radiative Decay, Exemplified by the 1,3‐Pentadiyne Cation , 1981 .

[10]  L. Cederbaum,et al.  Spectroscopic Effects of Conical Intersections of Molecular Potential Energy Surfaces: Photoelectron Spectra of the Cumulenes CnH4 (n= 2 ... 5) and of HCN , 1981 .

[11]  S. Iwata,et al.  The ab initio potential energy surfaces of some low‐lying states of acetylene , 1981 .

[12]  J. Pollard.  PHOTOELECTRON SPECTROSCOPY OF SUPERSONIC MOLECULAR BEAMS , 1981 .

[13]  S. Rice,et al.  Single vibronic level fluorescence from 1B3u pyrazine: The role of Fermi resonance and Duschinski rotation , 1981 .

[14]  A. J. Merer,et al.  Rotational analysis of bands at the long-wavelength end of the Ã2A2-X̃2B1 electronic transition of ClO2 , 1981 .

[15]  W. England.  Accurate ab initio scf energy curves for the lowest electronic states of co2/co−2 , 1981 .

[16]  F. Gerson,et al.  Radical Cations of Sterically Hindered Bicycloalkylidenes: An Experimental Contribution Concerning the Planarity of the Ethylene Radical Cation , 1981 .

[17]  K. Swift,et al.  Vibronic assignments and vibronic coupling in the 1E′′ state of sym‐triazine by two photon spectroscopy , 1980 .

[18]  A. J. Merer,et al.  Orbital angular momentum in triatomic molecules: I. A general method for calculating the vibronic energy levels of states that become degenerate in the linear molecule (the Renner-Teller effect) , 1980 .

[19]  A. J. Merer,et al.  Orbital angular momentum in triatomic molecules , 1980 .

[20]  C. Jackels.  An ab initio potential‐energy surface study of several states of the water cation , 1980 .

[21]  D. McClure,et al.  Vibronic Interactions in the Naphthalene Molecule , 1980 .

[22]  M. Zgierski.  Theoretical analysis of vibronic coupling in the lowest T1[3A'2(ππ*)] state of triphenylene-h12 and-d12 , 1980 .

[23]  J. Sell,et al.  Variable angle photoelectron spectroscopy of the fluoroethylenes , 1979 .

[24]  J. Maier,et al.  à 2A1 → X̃ 2B1 emission spectrum of cis-1,2-difluoroethylene cation and the non-radiation decay of the à states of the haloethylene cations in the gaseous phase , 1979 .

[25]  M. Desouter-Lecomte,et al.  Nonadiabatic interactions in unimolecular decay. V. Conical and Jahn–Teller intersections , 1979 .

[26]  A. Kuppermann,et al.  Photoelectron spectroscopy of ethylene, isobutylene, trimethylethylene, and tetramethylethylene at variable angle , 1979 .

[27]  L. Goodman,et al.  Coupling of electronic and vibrational motions in molecules , 1979 .

[28]  L. Cederbaum,et al.  Vibronic coupling in linear molecules and linear-to-bent transitions: HCN , 1979 .

[29]  W. B. Englandb,et al.  Theoretical studies of atmospheric triatomic molecules. New abinitio results for the 1Πg–1Δu vertical state ordering in CO2a) , 1979 .

[30]  G. Fischer,et al.  The double minimum potential in the spectrum of HCOF , 1979 .

[31]  P. Ausloos.  Kinetics of Ion-Molecule Reactions , 1979 .

[32]  J. Brand,et al.  Asymmetric structure and force field of the 1B2(1A′) state of sulphur dioxide , 1978 .

[33]  L. Cederbaum,et al.  Vibronic coupling effects in the photoelectron spectrum of ethylene , 1978 .

[34]  L. Cederbaum,et al.  Jahn—Teller effect induced by non-degenerate vibrational modes in cumulenes , 1978 .

[35]  W. H. Henneker,et al.  Exactly solvable models for vibronic coupling in molecular spectroscopy. III. The pseudo Jahn–Teller effect , 1978 .

[36]  E. Krausz,et al.  Vibronic coupling model for calculation of mixed valence absorption profiles , 1978 .

[37]  N. D. Epiotis,et al.  Structure of fluoromethyl radicals. Conjugative and inductive effects , 1978 .

[38]  E. Heilbronner,et al.  The Photoelectron Spectrum of Tetrafluorobutatriene , 1978 .

[39]  L. Cederbaum,et al.  Strong vibronic coupling effects in ionization spectra: The “mystery band” of butatriene , 1977 .

[40]  W. Gelbart,et al.  Nonradiative electronic relaxation under collision-free conditions , 1977 .

[41]  H. Bock.  Molecular States and Molecular Orbitals , 1977 .

[42]  H. Bock.  Molekülzustände und Molekülorbitale , 1977 .

[43]  M. Zgierski.  Some comments on vibronic intensities of naphthalene fluorescence spectra from single vibronic levels , 1977 .

[44]  E. Heilbronner,et al.  The Electronic States of the Pentatetraene Radical Cation , 1977 .

[45]  E. Davidson.  Global topology of triatomic potential surfaces , 1977 .

[46]  Paul H. Krupenie,et al.  The spectrum of molecular nitrogen , 1977 .

[47]  R. Silbey,et al.  Vibronic coupling by two active modes: A simple, exactly solvable model for the Duschinsky effect , 1976 .

[48]  I. G. Ross,et al.  Vibronic coupling by out-of-plane modes in pyridine,pyrazine and quinoxaline , 1976 .

[49]  J. Brickmann.  Mechanisms of Non Resonance Vibronic Coupling in Polyatomic Molecules , 1976 .

[50]  K. Houk,et al.  Photoelectron spectra of sterically congested alkenes and dienes , 1976 .

[51]  H. Trommsdorff,et al.  Vibronic mixing and vibronic coupling of nearby electronic states. II: CNDO calculations of vibronic mixing in p‐benzoquinone , 1976 .

[52]  Ernest R. Davidson,et al.  The two lowest energy 2A′ states of NO2 , 1976 .

[53]  K. Freed.  Energy dependence of electronic relaxation processes in polyatomic molecules , 1976 .

[54]  R. N. Yardley,et al.  Investigation of the 2B2 state of H2O+ using valence-bond techniques , 1975 .

[55]  H. C. Longuet-Higgins.  The intersection of potential energy surfaces in polyatomic molecules , 1975, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[56]  M. Inghram,et al.  Vibrational structure in the ground state of ethylene and ethylene-d4 molecular ions investigated by threshold photoelectron spectroscopy , 1975 .

[57]  J. Egmond,et al.  Vibronic interaction in the lower electronic states of benzene , 1974 .

[58]  G. Schwenzer,et al.  Geometries of the excited electronic states of HCN , 1974 .

[59]  L. Radom,et al.  The photoelectron spectrum of butatriene , 1974 .

[60]  J. Dubois,et al.  Alkene ionization potentials: Part I: Quantitative determination of alkyl group structural effects , 1973 .

[61]  G. Fischer,et al.  Jahn‐Teller Distortion of s‐Triazine in Its Lowest Excited Singlet State , 1972 .

[62]  R. Fulton.  Vibronic Interactions. The Adiabatic Approximation , 1972 .

[63]  C. R. Brundle,et al.  The vibrational structure in the photoelectron spectra of ethylene and ethylene-d4, and its relationship to the vibrational spectrum of Zeise's salt K[PtCL3(C2H4)]·H2O , 1971 .

[64]  R. Pearson.  Symmetry rules for chemical reactions , 1971 .

[65]  Sean P. McGlynn,et al.  Electronic spectoscopy of isoelectronic molecules. II. Linear triatomic groupings containing sixteen valence electrons , 1971 .

[66]  E. Haselbach.  Jahn-Teller distortions in the radical cations of cyclopropane and allene , 1970 .

[67]  C. R. Brundle,et al.  Experimental and theoretical comparison of the electronic structures of ethylene and diborane , 1970 .

[68]  M. El-Sayed,et al.  Ionization Potential and Structure of Olefins , 1970 .

[69]  D. C. Frost,et al.  Photoelectron Spectra of Ethylene and Ethylene‐d4 , 1970 .

[70]  A. J. Merer,et al.  Ultraviolet spectra and excited states of ethylene and its alkyl derivatives , 1969 .

[71]  E. C. Lim,et al.  Vibronic Interactions between nπ* and ππ* States of Polycyclic Azines and Aromatic Aldehydes: A Study of Perturbing Vibrations from Phosphorescence Spectra , 1969 .

[72]  C. Perrin,et al.  Vibronic Coupling. VI. Vibronic Borrowing in Cyclic Polyenes and Porphyrin , 1969 .

[73]  G. C. Nieman.  Molecular Distortions and the Phosphorescence of Benzene , 1969 .

[74]  L. Salem.  Conditions for favorable unimolecular reaction paths , 1969 .

[75]  D. W. Turner,et al.  The electronic structures of methane, ethane, ethylene and formaldehyde studied by high-resolution molecular photoelectron spectroscopy , 1968 .

[76]  R. Hochstrasser,et al.  Perturbations between Electronic States in Aromatic and Heteroaromatic Molecules , 1968 .

[77]  R. Lefebvre,et al.  Intensity Patterns in Absorption and Fluorescence Spectra of Molecular Dimers: A Comparison between the Vibronic and the Born–Oppenheimer Approach , 1968 .

[78]  M. Gouterman,et al.  Vibronic Coupling. IV. Trimers and Trigonal Molecules , 1967 .

[79]  A. Berghuis,et al.  Vibronic interaction in the lower electronic states of benzene: I. Review of the static problem and solution of the pseudo-cylindrical vibronic equations , 1967 .

[80]  J. B. Coon,et al.  The investigation of double-minimum potentials in molecules , 1966 .

[81]  W. D. Hobey.  Vibronic Interaction of Nearly Degenerate States in Substituted Benzene Anions , 1965 .

[82]  M. Gouterman,et al.  Vibronic Coupling. II. Spectra of Dimers , 1964 .

[83]  B. Kleman.  THE NEAR-ULTRAVIOLET ABSORPTION SPECTRUM OF CS2* , 1963 .

[84]  R. Bader.  VIBRATIONALLY INDUCED PERTURBATIONS IN MOLECULAR ELECTRON DISTRIBUTIONS , 1962 .

[85]  M. Gouterman,et al.  Vibronic Coupling. I. Mathematical Treatment for Two Electronic States , 1961 .

[86]  A. Witkowski,et al.  Electronic Spectra of Dimers: Derivation of the Fundamental Vibronic Equation , 1960 .

[87]  A. C. Albrecht.  ``Forbidden'' Character in Allowed Electronic Transitions , 1960 .

[88]  R. S. Mulliken.  Conjugation and hyperconjugation: a survey with emphasis on isovalent hyperconjugation , 1959 .

[89]  H. C. Longuet-Higgins,et al.  Studies of the Jahn-Teller effect .II. The dynamical problem , 1958, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[90]  W. Moffitt,et al.  Configurational Instability of Degenerate Electronic States , 1957 .

[91]  D. W. Scott,et al.  2,3-Dimethyl-2-butene: Thermodynamic Properties in the Solid, Liquid and Vapor States , 1955 .

[92]  Michael Kasha,et al.  Characterization of electronic transitions in complex molecules , 1950 .

[93]  T. Koopmans,et al.  Über die Zuordnung von Wellenfunktionen und Eigenwerten zu den Einzelnen Elektronen Eines Atoms , 1934 .