Selective Intracluster Ion‐Chemistry Studied by Resonant Two‐Photon Ionization Spectroscopy

Abstract

After resonant two‐photon ionization of mixed clusters of substituted aromatics with polar and unpolar solvents we observed very selective intracluster relaxation reactions. They are assumed to take place in the cationic complexes. The selectivity of a nucleophilic substitution reaction of halogenated benzenenes with nucleophiles is rationalized by different isomeric structures of the neutral aggregates. Proton transfer from ionized methylated benzenes to polar solvents is found to be governed by the solvent's proton solvation energetics. Electron transfer, at present studied only for ether compounds as solvent, takes place, if the ionization potential of the solute is larger than of the solvent.

Characterization of Weak NH−π Intermolecular Interactions of Ammonia with Various Substituted π-Systems

“…Toluene/Ammonia Cluster. The R2PI spectrum of the system Tol − Am has been reported previously in detail. , The spectrum of the 1:1 + complex is monitored by the yield of the (NH 3 )H + ion. The latter is the product of a dissociative proton-transfer reaction taking place in the (1:1) + complex.…”

“…It shows two sharp and intense bands. The spectrum of the ClBz·Am cluster was recorded in the ion channel of the anilinium + ion, which appears as a product of a fast and nearly quantitative nucleophilic substitution reaction between chlorobenzene + and ammonia. ,, Similar to the spectrum of the T π 1 isomer of Tol − Am , the asymmetric vibration is split up by 11.1 cm -1 (marked with arrows). The spectrum of the pDFBz·Am complex resembles only superficially that of the ClBzAm complex: both clusters exhibit a ν 3 splitting.…”

Reactive Pathways in the Chlorobenzene–Ammonia Dimer Cation Radical: New Insights from Experiment and Theory

“…The dimers of halobenzenes with ammonia are model systems for understanding the effects of complex formation on bimolecular reactions, as found initially by Brutschy and co-workers. , In a 1988 communication and a later report in 1990, Maeyama and Mikami showed that ionization of the PhCl···NH 3 complex resulted in Cl atom loss to yield protonated aniline (anilinium ion), through an intracluster S N 2 reaction from the ionized complex . The origin band of the S 0 –S 1 spectrum of the complex was blue-shifted from the monomer (PhCl) origin by ∼76 cm –1 , and while no information on the structure of the complex was obtained, the following reaction scheme was postulated: C 6 H 5 Cl ··· N H 3 → 2 h ν [ C 6 H 5 Cl ··· N H 3 ] + • → [ C 6 H 5 Cl−N H 3 ] + • → [ C 6 H 5 N H 3 ] + + Cl • Brutschy and co-workers conducted similar R2PI studies on fluorobenzene, chlorobenzene, and p -chlorofluorobenzene complexes with methanol and ammonia. − In the case of the PhF···NH 3 dimer, a blue-shifted (∼58 cm –1 ) feature was observed in the S 0...…”

“…39−81 The dimers of halobenzenes with ammonia are model systems for understanding the effects of complex formation on bimolecular reactions, as found initially by Brutschy and coworkers. 82,83 In a 1988 communication and a later report in 1990, Maeyama and Mikami showed that ionization of the PhCl•••NH 3 complex resulted in Cl atom loss to yield protonated aniline (anilinium ion), through an intracluster S N 2 reaction from the ionized complex. 76 The origin band of the S 0 −S 1 spectrum of the complex was blue-shifted from the monomer (PhCl) origin by ∼76 cm −1 , and while no information on the structure of the complex was obtained, the following reaction scheme was postulated: (1)…”

Reactivity and Electronic Structures of Isolated Clusters

“…Another class of photon induced reactions occurs in solvated clusters of fluorobenzene and para-difluorobenzene [67,68]. Fluorobenzene solvated with methanol can be transformed into the ionic state by R2 PI.…”