Solvent Migration in Microhydrated Aromatic Aggregates: Ionization‐Induced Site Switching in the 4‐Aminobenzonitrile–Water Cluster |
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Authors: | Takashi Nakamura Dipl‐Phys Matthias Schmies Dipl‐Phys Alexander Patzer Prof Dr Mitsuhiko Miyazaki Prof Dr Shun‐ichi Ishiuchi Dr Martin Weiler Prof Dr Otto Dopfer Prof Dr Masaaki Fujii |
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Institution: | 1. Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama 226‐8503 (Japan);2. Institut für Optik und Atomare Physik, Technische Universit?t Berlin, 10623 Berlin (Germany) |
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Abstract: | The dependence of the preferred microhydration sites of 4‐aminobenzonitrile (4ABN) on electronic excitation and ionization is determined through IR spectroscopy of its clusters with water (W) in a supersonic expansion and through quantum chemical calculations. IR spectra of neutral 4ABN and two isomers of its hydrogen‐bonded (H‐bonded) 4ABN–W complexes are obtained in the ground and first excited singlet states (S0, S1) through IR depletion spectroscopy associated with resonance‐enhanced multiphoton ionization. Spectral analysis reveals that electronic excitation does not change the H‐bonding motif of each isomer, that is, H2O binding either to the CN or the NH site of 4ABN, denoted as 4ABN–W(CN) and 4ABN–W(NH), respectively. The IR spectra of 4ABN+–W in the doublet cation ground electronic state (D0) are measured by generating them either in an electron ionization source (EI‐IR) or through resonant multiphoton ionization (REMPI‐IR). The EI‐IR spectrum shows only transitions of the most stable isomer of the cation, which is assigned to 4ABN+–W(NH). The REMPI‐IR spectrum obtained through isomer‐selective resonant photoionization of 4ABN–W(NH) is essentially the same as the EI‐IR spectrum. The REMPI‐IR spectrum obtained by ionizing 4ABN–W(CN) is also similar to that of the 4ABN+–W(NH) isomer, but differs from that calculated for 4ABN+–W(CN), indicating that the H2O ligand migrates from the CN to the NH site upon ionization with a yield of 100 %. The mechanism of this CN→NH site‐switching reaction is discussed in the light of the calculated potential energy surface and the role of intracluster vibrational energy redistribution. |
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Keywords: | cluster compounds hydrogen bonds IR spectroscopy isomerization solvation |
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