Photoionization-Induced Intracluster Reactions of Chlorobenzene/Ammonia Mixed Complexes

Article abstract of DOI:10.1021/j100082a016

Complexes of chlorobenzene and ammonia, C6H5Cl*NH3, C6H5Cl(NH3)2, and C6H5Cl(NH3)3, were studied by single-photon ionization.The ionization potentials of these three complexes were measured to be 8.744 +/- 0.022, 8.652 +/- 0.013, and 8.555 +/- 0.012 eV, respectively.The appearance potential of C6H5NH3⁺ from C6H5Cl*NH3 was found at 8.935 +/- 0.004 eV, which, with the known heat of formation of anilinium ion, gives the dissociation energy D(C6H5Cl*NH3) = 2.9 +/- 0.5 kcal mol^-1 (12.0 +/- 2.2 kJ mol^-1).Then, from its onset energy from C6H5Cl*NH3, the dissociation energy of (C6H5Cl*NH3)⁺ is calculated to be D<(C6H5Cl*NH3)⁺> = 10.4 +/- 0.7 kcal mol^-1 (43.5 +/- 2.9 kJ mol^-1), unusually large for a heterodimer ion.No production of C6H5NH3⁺ from trimers could be detected in the onset region.The ion C6H5NH2⁺ has onsets of 8.849 +/- 0.009 and 8.855 +/- 0.029 eV from C6H5Cl*NH3 and C6H5Cl(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, C6H5NH2⁺ 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 (C6H5Cl*NH3)⁺ and C6H5NH2⁺ are lower that for C6H5NH3⁺, then (C6H5Cl*NH3)⁺ in its ground state does not spontaneously form C6H5NH3⁺.Kinetic energy release distributions measured for C6H5NH2⁺ and C6H5NH3⁺ indicate that the formation of both ions is consistent with statistical process; i.e., no evidence for nonstatistical mechanisms was found, even for photon energies as large as 17.7 eV.