Vibrationally hot excited state

The adsorbed sensitizers in the excited state inject an electron into the conduction band of the semiconductor substrate, provided that the excited state oxidation potential is above that of the conduction band. The excitation of the sensitizer involves transfer of an electron from the metal t2g orbital to the 7r orbital of the ligand, and the photo-excited sensitizer can inject an electron from a singlet or a triplet electronically excited state, or from a vibrationally hot excited state. The electrochemical and photophysical properties of both the ground and the excited states of the dye play an important role in the CT dynamics at the semiconductor interface. 

Moser, J.E. and M. Gratzel (1998). Excitation-wavelength dependence of photo-induced charge injection at the semiconductor-dye interface Evidence for electron transfer from vibrationally hot excited states. Chimia 52, 160-162. 

If an electronically-excited state is formed as a vibrationally-hot excited molecule (with v > 0) then it will undergo vibrational relaxation within that electronic energy level until it reaches the v = 0 level. The vibrational relaxation within each electronically-excited state is drawn as a vertical wavy arrow. 

While vibrational excitation is important in spectroscopy, it is usually unimportant in photochemistry because the vibrationally excited excited state is really just a hot excited state containing a lot of excess thermal energy. This is lost extremely rapidly by collisions with surrounding molecules, so that chemical reactions in solution involve only the vibrational ground state. 

These complexes also demonstrate a change in the excited state character between a Frank-Condon (vibrationally hot ) electronically excited state and the vibrationally relaxed, lowest excited state. Resonance Raman (rR) spectra show that the vibrationally hot Franck-Condon states of [RuI(Me)(CO)2(iPr-DAB)] have virtually pure XLCT character [55]. However, the TRIR data indicate that thermally equilibrated, vibrationally-relaxed excited state has a mixed MLCT-XLCT character [6]. Hence, combining the results from resonance Raman and TRIR data allows one to obtain insight into charge redistribution processes in the excited state on a very short timescale. 

Photothermal decomposition, in which the electronically excited state undergoes internal conversion to a vibrationally ( hot ) excited ground states. Subsequent thermal decomposition is therefore a pyrolysis of the polymer, which is not very different from the processes observed with laser radiation at visible or infrared wavelengths [137,162,304,578,1240,1601]. 

Figure 13. Photodissociation spectrum of V (OCO), with assignments. Insets and their assignments show the photodissociation spectrum of molecules excited with one quanmm of OCO antisymmetric stretch, v" at 2390.9 cm . These intensities have been multiplied by a factor of 2. The shifts show that Vj (excited state) lies 24 cm below v ( (ground state), and that there is a small amount of vibrational cross-anharmonicity. The box shows a hot band at 15,591 cm that is shifted by 210 cm from the origin peak and is assigned to the V" -OCO stretch in the ground state.

Irradiation of benzaldehyde in the presence of S-decyne results in the formation of the above a,/3-unsaturated ketone, presumably from decomposition of an intermediate oxetene which may be formed in a vibrationally excited (hot) ground state.<106)... 

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