Vibronic Interaction of Nearly Degenerate States in Substituted Benzene Anions

Abstract

The pseudo-Jahn—Teller effect, the vibronic interaction of nearly degenerate electronic states, arises in the same manner as the Jahn—Teller effect itself. An iteration method, suitable for desk calculation, has been developed to allow computation of the vibronic wavefunctions and energies of a system with two closely spaced electronic states. A calculation on benzene anion compares favorably with previously published results. The method, in combination with semiempirical evaluation of the necessary parameters, has been applied to various substituted benzene anions and the ESR spectra of these anions predicted. The results compare satisfactorily with experiment and indicate that the spectra are the net result of three principal factors, configuration interaction among the simple molecular orbital electronic states, vibronic coupling, and thermal equilibrium between at least two vibronic states.

Vibronic effects on electron resonance spectra: the alkyl cyclooctatetraene anions

“…It has been suggested [1][2][3] that configuration interaction, vibronic coupling and thermal population of excited vibronic states will be important in a quantitative interpretation of these spectra. Recently Hobey [4] has examined the contribution of these effects to the electron resonance spectra of alkyl benzene anions; this paper considers the spectra of the alkyl cyclooctatetraene anions, which were observed by Carrington and Todd [2]. Their results support the hypothesis that the cyclooctatetraene anion and its alkyl derivatives are planar; other evidence has been summarized by McLachlan and Snyder [5] and planarity is assumed in this work without further comment.…”

“…Hobey's semi-empirical determination [4] gives 392 cm -1 and 328 cm -1 for the anions of toluene and ethyl benzene respectively. Our results for model IV are in close agreement with these, but a direct comparison is not legitimate for two reasons.…”

An isotopic and EPR probe into hyperconjugative and induction effects in p-xylene

“…This simple calculation leads to a AE of 437 1 J/mol at 195 K, which is very close to the empirical value found by Hobey (421 1 J/mol at 203 K) 3. If vibronic interactions are included, as carried out Abstract published in Advunce ACS Absrrucrs.…”

ESR. Spectra of the Radical Anions of Cycloalkylbenzenes

“…the energetic proximity of !PU+ and Pa-in monosubstituted alkyl derivatives of benzene (the relevant energy difference in toluene was estimated as 0.05 eV [S] [lo] [I1 1). 'Thermal interaction' and 'vibronic coupling' are generally thought to be responsible for orbital mixing of this kind [l] (51 [8] [lo] The ratio Y = (e2,6 +-e3,J/(el + e4) is therefore a sensitive function of this contribution; large (small) 7 values point to small (large) contributions of (@, )+ to (@+)-. It can be seen from the 5th column of Table 3 that Y varies between 1.9 (for V I P ) and 8.1 (for 10).…”