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Special Seminar
 
Name: Prof. G. Naresh Patwari
Affiliation: Department of Chemistry, IIT Bombay
 Title: Collective Excitation in Molecular Clusters
Date & Time: Tuesday, 15th April 2025 at 04:00 p.m.
    Venue: AG-09/11 Lecture Hall, Chemical Sciences Building
Abstract:
 

The origin of monomer cation upon 266 nm photoexcitation of nitrogenated (poly) aromatic heterocycle compounds is attributed to the dissociative photoionization of dimers based on time-of-flight mass spectrometry combined with velocity map ion imaging experiments [1]. The experiments performed in the presence and absence of buffer gas with varying laser intensities suggest that during neat expansion, monomer cations are formed via two-photon dependent resonantly enhanced multiphoton ionization (REMPI) while in the presence of buffer gas, (cluster formation enabled) broad translational energy distribution and three-photon dependence of monomers indicate dissociative photoionization of dimers as the origin. Interestingly, the REMPI of monomers appears at higher laser intensities in contrast to the three-photon dependent dissociative ionization of dimers that can occur even at lower laser intensities [2]. This contradicts the fact that the monomer concentrations are larger than those of clusters in the molecular beam and that the three-photon absorption should be less probable than two-photon absorption at lower intensities. These experimental results demonstrate that the interaction between monomer units in molecular clusters gives rise to cooperative/collective excitation phenomena that modifies the absorption cross-section, thereby enhancing multiphoton absorption compared to isolated monomers [3,4].

References: 

[1] J.T. Snodgrass, R.C. Dunbar, M.T. Bowers. J. Phys. Chem. 94 3648–3651 (1990).

[2] S. Kesari, A. Tagad, G.N. Patwari, https://arxiv.org/abs/2408.02981 (2024).

[3] A.C. Laforge, M. Drabbels, N.B. Brauer, M. Coreno, M. Devetta, M. Di Fraia, P. Finetti, C. Grazioli, R. Katzy, V. Lyamayev, T. Mazza, M. Mudrich, P. O’Keeffe, Y. Ovcharenko, P. Piseri, O. Plekan, K.C. Prince, R. Richter, S. Stranges, C. Callegari, T. Möller, F. Stienkemeier. Sci. Rep. 4, srep03621 (2014).

[4] F. Šanda, S. Mukamel. J. Chem. Phys. 124, 124103  (2006).