Vibrationally excited ground-state

The previous sections have shown that cis-trans isomerization of stilbene can take place via the lowest triplet state of stilbene. The question to be considered now is whether the isomerization upon direct photolysis takes place via the singlet state, the triplet state, or a vibrationally excited ground state.a 7 81 50)... 

In addition, this mechanism was criticized on the basis of the Kassel-Rice theory of vibrationally excited ground states some time earlier by Zimmerman et alS3i)... 

The photoaddition of acenaphthylene to cyclopentadiene was shown to be sensitive to the presence of heavy atoms in the solvent, as shown in Table 10.9. The data in Table 10.9 show that product (46) increases from 18% of the total product in cyclohexane to 38% of the total product in 1,2-dibromo-ethane. This suggests that the [4 + 2] cycloaddition products (47) and (48) and the [2 + 2] product (46) are produced from different excited states. Accordingly, some of the [4 + 2] product has been postulated to arise from either (a) a singlet excited state or (b) a vibrationally excited ground state... 

A thermal oxidation of 2,3-dimethyl-2-butene, 16, occurs in NaY when the temperature of the oxygen-loaded zeolite in raised above — 20°C [35], Similar thermally initiated oxidations were not observed for the less electron rich tram-or cix-2-butene. Remarkably, pinacolone was conclusively identified as one of the products of the reaction of 16, This ketone is not a product of the photochemical Frei oxidation (vide supra) and underscores the very different character of these two reactions and the complexity of the oxygen/16 potential energy surface, A rationale for the different behavior could lie in the different electronic states of the reactive oxygen-CT complex in the thermal and photochemical reactions. Irradiation could produce an excited triplet-state CT complex ( [16 O2] ) and/ or ion pair ( [16 02 ] ) with different accessible reaction channels than those available to a vibrationally excited ground-state triplet complex ( [16 "02]) and/... 

Excitations of molecules with femtosecond laser pulses lead to excited-state matter wave packets coherently, launching them with such well-defined spatial resolution and coherence in nuclear motions that they evolve like single-molecule trajectories. Both electronically excited and vibrationally excited ground-state species may be studied. The structural change versus time profile of a reaction turns out to be compatible with classical modes of thinking. 

Basco, Callear, and Norrish22,23 produced NO (v = 1) by a different method. They formed the A2 + state of NO with v = 0,1,2 (v is the vibrational quantum number in the electronically excited state) by direct irradiation. This state either fluoresces or is collisionally deactivated to give vibrationally excited ground-state molecules. Although several vibrational levels of the ground electronic state were... 

The corresponding naphthalene sulfone behaves similarly.37 No reaction is observed in the unsubstituted analog (34 R,=H) even in the presence of a sensitizer, and the extrusion of sulfur dioxide is therefore believed to occur in a vibrationally excited ground state. 

Formula 392 (173). The quantum yield for the formation of toluene in the vapor phase increases with decreasing pressure, the extrapolated value at zero pressure being one within experimental error (173). It has been suggested that the photoisomerization of cycloheptatriene to toluene involves a vibrationally excited ground state while the photoisomerization to the bicyclic product involves an electronically excited state (173). 

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