IVR in a Polyatomic Van der Waals Complex
We have studied the vibrational energy flow in photoexcited Van der Waals complexes T·Ar of s-tetrazine and argon. The aim of this paper is to present experimental information about the coupling among the Van der Waals vibrational modes in T·Ar and about the interaction between ring modes and vdW vibrations.
Time-resolved laser-induced fluorescence experiments have demonstrated that the photodissociation of T·Ar is preceded by intramolecular vibrational redistribution (IVR) processes in which the pumped level Ci develops into levels Cj of the complex which are not accessible by optical excitation because they include highly excited Van der Waals vibrations. The isoenergetic levels Ci and Cj of the cluster are characterized by different vibronic states of the tetrazine moiety.
The intensity patterns of the vibrational substructure of the fluorescence spectra indicate that the Van der Waals stretch and bend modes are extensively mixed. High resolution experiments performed with a single frequency laser show that the mixing of the pumped level Ci (in the present study 6a1) with near-resonant levels C (in this case 16a2) depends on the rotational state of the complex. The quantum yields of IVR and photodissociation depend on which rotational states of the cluster are initially excited. Almost all the selectivity with respect to the rotational degrees of freedom is in the first step (IVR) and not in the last step (fragmentation).
KeywordsManifold Benzene Argon Photodissociation Kelly
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