S2 State Photodissociation of Diphenylcyclopropenone, Vibrational Energy Transfer along Aliphatic Chains, and Energy Calculations of Noble Gas-Halide Clusters

In this work, three major topics are investigated. The decarbonylation of diphenylcyclopropenone from its second excited electronic state forms the first part. This reaction was investigated using pump laser pulses of several different wavelengths (267 nm and 295–340 nm). Earlier reports[1] that excited state diphenylacetylene is generated as a product are dismissed on three grounds. First, the intensity of the S1 state absorption of diphenylacetylene at 1553 cm−1 after decarbonylation of diphenylcyclopropenone was found to be much too weak. Second, ground state diphenylacetylene could be observed almost immediately within few picoseconds after the reaction had been triggered. Third, the pump wavelength limit of the appearance of the S1 state absorption of diphenylacetylene was very similar in both the direct excitation of diphenylacetylene and photo-decarbonylation of diphenylcyclopropenone. The alternative hypothesis of internal conversion followed by a hot ground state reaction[2] could not be substantiated. Hence it is concluded that this reaction proceeds non-adiabatically to the electronic ground state of the product. These findings have been corroborated by model calculations and observations of the visible to near-UV transient spectra reported elsewhere[3]. In the main part, the investigation of IVR in several azulenyl-acetamides with aliphatic side chains of different lengths is reported. Three marker bands were monitored to assess the progress of intramolecular vibrational energy transport (IVR) after excitation of the azulene moiety to its S1 state at 610 nm and the well-known subsequent internal conversion: an azulene ring distortion mode, the amide I mode of the acetamide, and a characteristic mode of a group installed at the opposite end of the chain, i.e. either an asymmetric azide stretching mode or a carbonyl mode. The side chains themselves consisted of methylene groups or ethylene glycol oligoethers. The velocity of energy loss from the azulene group – in agreement with previous research[4] – could be confirmed to saturate with increasing chain length. Energy transport was found to occur fast, with transport times approximately proportional to chain length, as reported earlier for similar systems[5], and hence concluded to be ballistic in nature. Transport efficiency, on the other hand, was found to decay greatly with chain length. Finally, the amide group presented a suitable reporter for intermediate steps of IVR, exhibiting a distinct spectral response during the progress of energy redistribution. Efforts to shed light on the underlying cause of this phenomenon as well as on the spectral signatures of the other observed marker bands through constants of anharmonicity did not yield conclusive results. The setup used for both of these experimental works consisted of a transient difference IR spectrometer using laser pulses of roughly 100 fs width, capable of monitoring the range from 1250 to 2400 cm−1. The third part is devoted to weakly bound halide–noble gas clusters and motivated by an earlier experimental work[6] with a special focus on contributions to the potential energy which are not additive in a pairwise fashion. Two improvements are proposed to a description of those systems put forth by Yourshaw and coworkers[7]: A linear algebraic calculation of non-additive effects in electrostatic induction and a concise analytic solution to the |jmj> -Hamiltonian governing the interaction of a 2P atom (halide) with a number of closed shell atoms (noble gas). Subsequently, calculations of the electron affinities of the species investigated experimentally[6] are presented, covering a much greater number of systems than previously discussed[7–9]. While the theoretical values are qualitatively in agreement with most of the experimental data, quantitative agreement appears to be hampered by the imprecision of the binary potentials used. In particular, inaccuracies in equilibrium distances appear to be amplified by non-additive contributions to the potential energy. For fluorine-containing clusters, except those with argon, the description is dissatisfying even at a qualitative level. [1] Y. Hirata and N. Mataga, Chemical Physics Letters 193, 287 (1992). [2] L. T. Nguyen, F. De Proft, M. T. Nguyen, and P. Geerlings, Journal of the Chemical Society, Perkin Transactions 2 6, 898 (2001). [3] H. Vennekate, A. Walter, D. Fischer, J. Schroeder, and D. Schwarzer, Zeitschrift f¨ ur Physikalische Chemie 225, 1089 (2011). [4] D. Schwarzer, P. Kutne, C. Schroder, and J. Troe, The Journal of Chemical Physics 121, 1754 (2004). [5] Z. Lin, N. Zhang, J. Jayawickramarajah, and I. V. Rubtsov, Physical Chemistry Chemical Physics 14, 10445 (2012). [6] M. Kopczynski, Femtosekunden Photodetachment- Photoelektronenspektroskopie an isolierten und massenselektierten Halogen-Edelgas-Clustern, Ph.D. thesis, Georg-August-University (2010). [7] I. Yourshaw, Y. Zhao, and D. M. Neumark, The Journal of Chemical Physics 105, 351 (1996). [8] T. Lenzer, M. R. Furlanetto, N. L. Pivonka, and D. M. Neumark, The Journal of Chemical Physics 110, 6714 (1999). [9] T. Lenzer, I. Yourshaw, M. R. Furlanetto, N. L. Pivonka, and D. M. Neumark, The Journal of Chemical Physics 115, 3578 (2001)