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Journal of the Physical Society of Japan

Theory of Indirect Dephasing Model for a Vibrating Molecule in Dense Mediums. II

Eiko Hiroike

Published Jun 1, 1982• 3 citations
Publisher

Abstract

The indirect dephasing model for a vibrating molecule in a dense medium is succesively investigated by using the formulas obtained in the previous paper by the author. The line-shape function for the spectrum of the high-frequency mode is obtained, and the dependence of the line-width of the spectrum on the life-time of the excited state of the low-frequency mode is discussed.

DOI
10.1143/jpsj.51.1953

Related papers

Theory of Indirect Dephasing for a Vibrating Molecule in Dense Mediums. I

Eiko Hiroike

The indirect dephasing model for a vibrating molecule in a dense medium is investigated by using the cumulant perturbation expansion method. The perturbation is taken as a sum of the anharmonic coupling between the high- and low-frequency modes and the interaction between the low-frequency mode and molecular surrounding. All the states of the low-frequency mode is taken into account in the calculation. Our model is available, only when the dephasing time of the high-frequency mode is shorter than the life-time of the low-frequency mode. This condition is satisfied in usual organic molecular crystals.

Journal of the Physical Society of Japan•Mar 1, 1982•8 citations

Theory of Indirect Dephasing for a Vibrating Molecule in Dense Mediums. III

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The dephasing of a high-frequency intramolecular vibrational mode in a molecular crystal is successively investigated by the cumulant perturbation expansion method as in the preceding papers in this series, I and II. The dephasing of the high-frequency mode is brought on by the thermal excitation of a low-frequency mode in the same molecule as in I and II. In this paper, however, the intramolecular vibrational modes are expressed by the bands of the exciton waves traveling through the crystal (in I and II, the intramolecular vibrational modes are expressed by the localized excitation in one molecule). The calculation shows that the spectrum becomes considerably broad as the temperature increases, while the narrowing is observed as the band widths of the exciton waves increases.

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Abstract Starting from quantum theoretical principles the phase relaxation is described of a molecule localized in a dense medium by an integro‐differential equation. Using this equation, which leads to a non‐exponential phase decay, general formulas are derived for calculating the absorption and dispersion profiles of vibronic and vibrational transitions of the guest molecule. In detail the calculations are performed for the case that the acoustic phonons of the medium are responsible for the phase relaxation. Especially it is shown, that in comparison with the Lorentz profile the wings of a real absorption profile become steeper with increasing ratio between dephasing rate y and Debye frequency wD‐ Only for γ/wD ≪ 1 the absorption profiles are expected to be Lorentz profiles. The dispersion is found to increase with increasing ratio γ/wD. Both the real absorption and dispersion curves are asymmetric ones.

physica status solidi (b)•Aug 1, 1977•2 citations

Dependence of the coherence spike on the material dephasing time in pump–probe experiments

Michael W. Balk, Graham R. Fleming

The coherence spike observed in the transmitted probe intensity decay curve in pump–probe experiments is analyzed with a model which depends explicitly upon the population decay and dephasing rate constants. Using this model and simple pulse shape functions a series of decay curves are calculated throughout the range of wide to narrow pulse widths relative to the dephasing time. These calculations suggest that the coherence spike may be used to obtain information about the phase coherence in the electronic or vibrational transition being investigated, when the pulse width is comparable to or smaller than the dephasing time. Methods of extracting T2 from the coherence spike are also discussed.

The Journal of Chemical Physics•Nov 1, 1985•52 citations
The indirect dephasing model for a vibrating molecule in a dense medium is succesively investigated by using the formulas obtained in the previous paper by the author. The line-shape function for the spectrum of the high-frequency mode is obtained, and the dependence of the line-width of the spectrum on the life-time of the excited state of the low-frequency mode is discussed.
The indirect dephasing model for a vibrating molecule in a dense medium is investigated by using the cumulant perturbation expansion method. The perturbation is taken as a sum of the anharmonic coupling between the high- and low-frequency modes and the interaction between the low-frequency mode and molecular surrounding. All the states of the low-frequency mode is taken into account in the calculation. Our model is available, only when the dephasing time of the high-frequency mode is shorter than the life-time of the low-frequency mode. This condition is satisfied in usual organic molecular crystals.
The dephasing of a high-frequency intramolecular vibrational mode in a molecular crystal is successively investigated by the cumulant perturbation expansion method as in the preceding papers in this series, I and II. The dephasing of the high-frequency mode is brought on by the thermal excitation of a low-frequency mode in the same molecule as in I and II. In this paper, however, the intramolecular vibrational modes are expressed by the bands of the exciton waves traveling through the crystal (in I and II, the intramolecular vibrational modes are expressed by the localized excitation in one molecule). The calculation shows that the spectrum becomes considerably broad as the temperature increases, while the narrowing is observed as the band widths of the exciton waves increases.
Abstract Starting from quantum theoretical principles the phase relaxation is described of a molecule localized in a dense medium by an integro‐differential equation. Using this equation, which leads to a non‐exponential phase decay, general formulas are derived for calculating the absorption and dispersion profiles of vibronic and vibrational transitions of the guest molecule. In detail the calculations are performed for the case that the acoustic phonons of the medium are responsible for the phase relaxation. Especially it is shown, that in comparison with the Lorentz profile the wings of a real absorption profile become steeper with increasing ratio between dephasing rate y and Debye frequency wD‐ Only for γ/wD ≪ 1 the absorption profiles are expected to be Lorentz profiles. The dispersion is found to increase with increasing ratio γ/wD. Both the real absorption and dispersion curves are asymmetric ones.
The coherence spike observed in the transmitted probe intensity decay curve in pump–probe experiments is analyzed with a model which depends explicitly upon the population decay and dephasing rate constants. Using this model and simple pulse shape functions a series of decay curves are calculated throughout the range of wide to narrow pulse widths relative to the dephasing time. These calculations suggest that the coherence spike may be used to obtain information about the phase coherence in the electronic or vibrational transition being investigated, when the pulse width is comparable to or smaller than the dephasing time. Methods of extracting T2 from the coherence spike are also discussed.