Photoionization-Induced Intracluster Reactions of Chlorobenzene/Ammonia Mixed Complexes

Abstract

Complexes of chlorobenzene and ammonia, C6H5ChNH3, C,&Cl(NH3)2, and C&I5Cl(NH3)3, were studied by single-photon ionization. The ionization potentials of these three complexes were measured to be 8.744 f 0.022, 8.652 f 0.013, and 8.555 f 0.012 eV, respectively. The appearance potential of C6HsNH3+ from C6H5CbNH3 was found at 8.935 f 0.004 eV, which, with the known heat of formation of anilinium ion, gives the dissociation energy D(c6H~cbNH3) = 2.9 f 0.5 kcal mol-' (12.0 f 2.2 kJ mol-'). Then, from its onset energy from C6H5ChNH3, the dissociation energy of ( C~H S C~. N H~) + is calculated to be D[(C6H&l.NH3)+] = 10.4 f 0.7 kcal mol-' (43.5 f 2.9 kJ mol-'), unusually large for a heterodimer ion. No production of C&NH3+ from trimers could be detected in the onset region. The ion C&NH2+ has onsets of 8.849 f 0.009 and 8.855 f 0.029 eV from C6HsCbNH3 and C6H&l(NH3)2, respectively. These energies are below the onset for C6H5NH3+ but far above the thermochemical thresholds for aniline ion, which are near 7.6 eV. Evidently, C6HsNH2+ is not produced by dissociative ionization of the excited neutral complex. Instead, the complex must first be ionized and excited to at least 0.1 eV. Since the onsets for (C~HSCI*NH~)+ and C&NH2+ are lower than for C&NH3+, then (C&Cl-NH3)+ in its ground state does not spontaneously form CaH5NH3+. Kinetic energy release distributions measured for C&NH2+ and CaH5NH3+ indicate that the formation of both ions is consistent with statistical processes; i.e., no evidence for nonstatistical mechanisms was found, even for photon energies as large as 17.7 eV.

Chemical Reactivity in Microscopic Systems: The Nucleophilic Substitution of Halogenated Benzene Ions by Ammonia Studied in Molecular Clusters

“…The energetics deduced for pFBrB-NH3 complexes are displayed in the diagram of Figure 11. C. Chlorobenzene-Ammonia (1-1) Complex. The reactivity of chlorobenzene-NH3 complexes has been recently reinvestigated by single photon ionization (SPI) with synchrotron radiation by Grover et al 13 The results are very similar to those we obtained on m-and p-fluorochlorobenzene-NH3 systems. Three thresholds are measured when increasing the energy: the vertical ionization threshold at 70 520 cm"™1; the aniline"1" appearance threshold at 71 370 cm™1; and the anilinium appearance threshold at 72 060 cm™1.…”

“…Figure 13 presents a mass spectrum recorded when the 0® band of the chlorobenzene-NH3 complex is excited. We have checked that the aniline"1" comes from the resonantly excited 1-1 complex and not from larger sized clusters.…”

Styrene Clusters in a Supersonic Jet: Reactive and Nonreactive Systems

“…[1][2][3] Nonetheless, the number of reactive systems studied that way is very limited, particularly when compared to the large number of nonreactive systems that were studied. [4][5][6] Most studies dealt with ionic species, [7][8][9][10] atom transfer reactions, 1,[11][12][13][14] and proton transfer. [15][16][17][18] Exciplex formation in jets was extensively studied, being easily recognized by the appearance of a charge transfer type fluorescence.…”

“…The study of samples of 1:1 clusters, easily generated in supersonic expansions, can in principle elucidate details of bimolecular reactions that are difficult to observe in bulk systems. − Nonetheless, the number of reactive systems studied that way is very limited, particularly when compared to the large number of nonreactive systems that were studied. − Most studies dealt with ionic species, − atom transfer reactions, ,− and proton transfer. − Exciplex formation in jets was extensively studied, being easily recognized by the appearance of a charge transfer type fluorescence. − The initially excited state in these systems is usually a locally excited (LE) state, showing that when energetically possible, the formation of an exciplex competes successfully with other processes in the system, including dissociation into the original constituents. These systems were also subject to several theoretical studies in which the nature of the excited states was elucidated by empirical or semiempirical methods. , …”

Resonant two-photon ionization spectra of van der Waals complexes p, m, o-C6H4F2⋯NH3(ND3)

“…19 Studies on the intracomplex ion-molecule reactions following photoionization of C 6 H 5 X¯͑NH 3 ͒ n (Xϭhalogen) have been reported recently. [20][21][22] The R2PI spectrum of C 6 H 5 F¯NH 3 shows that this complex has two conformations; 20 one is with NH 3 being above the benzene ring and far from the F atom, and the other is with NH 3 being close to the F atom, forming a hydrogen bond. The latter is susceptible to substitution of F by NH 3 once activated, leading to the formation of a protonated aniline moiety.…”