Vibrational progressions in vibronically induced transitions

Abstract

Articles you may be interested inTheoretical modeling of UV-Vis absorption and emission spectra in liquid state systems including vibrational and conformational effects: Explicit treatment of the vibronic transitions It is shown that progressions of totally symmetric vibrations in vibronically induced spectra do not show the same intensity distribution as comparable progressions in allowed spectra. This is due to cross terms. involving both totally symmetric and inducing mode coordinates, in the Herzberg-Teller expansion. These cross terms express the modulation of the vibronic coupling resulting from differences in interatomic distances between the borrowing and lending states. The effect is universal, as opposed to effects based on normal-coordinate rotation or totally symmetric inducing modes. and enters even in the absence of anharmonic coupling. It leads to anomalous intensity distributions which, moreover, are different for emission and absorption spectra. Quantitative estimates are presented which indicate that it should be readily observable in many molecules.(3)

Absorption and circular dichroism spectra of dimeric systems. Extended dimer model

“…Using Eqs. (24), (25), and (27), we obtain (29) shifted to higher energy by the same amount. This is a familiar result of the pure electronic treatment.…”

“…These "higher-order" Franck-Condon effects which destroy the Poisson-type intensity distribution among the members of a totally symmetric progression have been recognized before in the induced parts of absorption-emission spectra of polyatomic molecules, and are known as non-Condon effects. [29][30][31][32] The solutions of Eq. (16) will be found numerically by expanding the functions a!, {3!…”

“…Accordingly, with the transformation (22) and Eq. (29), the approximate total vibronic wave function of the extended dimer model may be written in the form…”

“…For 13m ¢ f3 n , however, also the totally symmetric intensity distributions are changed, namely in a manner similar to that of vibrationally induced totally symmetric progressions in molecules (non-Condon effects). [29][30][31][32] The smaller is the ratio of transition dipole moments Dml D n , the stronger will be the non-Condon effects visible in the absorption spectrum in the region of the 1m )th monomer state.…”

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

“…Toward the band maximum, it becomes positive and reaches a plateau ( R ≈ +0.2). This low anisotropy value can be interpreted by the Herzberg−Teller coupling mechanism − in terms of a vibronic mixing, borrowing the intensity in the axial direction from the somewhat higher lying and more intense transition to the 1 L a state (as in Figures and ).

28 Spectra of 1 in n -propanol at T = 103 K. Solid curves, corrected fluorescence (left) and excitation spectra (right); open points, fluorescence anisotropy, excited at 32 500 cm -1 ; full points, excitation anisotropy, monitored at 29 000 cm -1 .

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