Optical transition in an impurity centre of a crystal: Mixing of phonons

Effects of mode-mixing and non-Condon interaction in the vibronic spectra of multimode systems

“…For a6 ¼0 the Airy oscillations appear. This-type spectra resemble the structure observed experimentally in the optical spectra of small molecules in superfluid 4 He droplets [8].…”

“…To solve the problem we applied the path integral-type method proposed in Ref. [4] and generalized it, taking into account the Herzberg-Teller (non-Condon) interaction. On using this method the shapes of the spectra for the different values of the parameter a of the linear vibronic coupling and the parameter b of the quadratic vibronic coupling close to its critical value (which corresponds to the border of the dynamical instability of the excited state) were calculated in the case of zero temperature.…”

“…Nevertheless, as it was shown in Ref. [4], it works also when the number of contributing modes is small and the temperature is zero. Thus, the problem of the calculation of the Fourier transform of the spectrum is reduced to the calculation of the determinant of the N Â N symmetric complex matrix I-itbD/N and its reciprocal matrix.…”

“…In high-symmetry centres, as a rule, only one q l contributes essentially to the given row of the given representation (the case when there is more than one such coordinate can be generalized analogously as it was done in Ref. [4] in the Condon approximation). The contributions of the different coordinates q l to F are then independent of each other and the Fourier transform becomes equal to the product Q l F l ðtÞ, where F l (t) is given by Eq.…”

Soft dynamics of the excited state: Lambda-shaped optical spectra

“…[21] by applying the new numerical method proposed in Ref. [22]. The calculations have been done for the modified Debye model, which gives a correct description of low-frequency phonons.…”