Stokes shifting Stretching mode

These spectra show uniformly three resolved vibrational components, the second component being always the strongest. The vibrational spacings fall in the range 1600—1200 cm, usual values for C—C stretching modes of conjugated polyenes. The Stokes shifts of 44 and 46 are notably small especially when compared to those of the cis-1,2-diarylethylenes ... 

Here, S is the Huang-Rhys factor [63], which is related to the intensity of the 0-n vibronic transition, Io-n = e sSn/n, and reflects the time-dependent Stokes shift associated with a given type of vibrational mode (e.g., S 0.6 for the high-frequency C=C stretch modes [61,64,65]). For the class of systems studied here, two types of phonon modes are considered per monomer unit, i.e., high-frequency C=C stretch modes and low-frequency ring-torsional modes. 

Repeat the operation with a second cell filled with denterated benzene, CsDg. In this case the Stokes shift for the CD stretching mode is mnch smaller, and this beam is expected to occur between the second and third Stokes spots prodnced by the CC stretch. This fea-tnre is less intense than its CH connterpart in CsHg, bnt it shonld be observable, along with the fourth I cc-shifted Stokes feature. 

The excitation spectrum of CaS04 Bi shows structured features at liquid-helium temperature. The absorption progression of Sq —> Pi starts from ZPL at 366.6 nm, and the vibrational lines are separated by an energy interval of approximately 430 cm , which is due to the stretching mode of Bi-O. The ZPL difference between 366.6 and 367.6 nm is perhaps due to self-absorption [49]. The Huang-Rhys factor is 1.5, and it shows a weak coupling between the electron and the phonons in the host. It therefore leads to a small offset of the excited state and then a small Stokes shift. 

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