PHOTOIONIZATION-INDUCED INTRACLUSTER REACTIONS OF CHLOROBENZENE AMMONIA MIXED COMPLEXES/

Complexes of chlorobenzene and ammonia, C6H5Cl.NH3, C6H5Cl(NH3)(2), an d C6H5Cl(NH3)(3), were studied by single-photon ionization. The ioniza tion 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 app earance potential of C6H5NH3+ from C6H5Cl.NH3 was found at 8.935 +/- 0 .004 eV, which, with the known heat of formation of anilinium ion, giv es the dissociation energy D(C6H5Cl.NH3) = 2.9 +/- 0.5 kcal mol(-1) (1 2.0 +/- 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)), unusu ally large for a heterodimer ion. No production of C6H5NH3+ from trime rs 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(N H3)(2), respectively. These energies are below the onset for C6H5NH3but far above the thermochemical thresholds for aniline ion, which are near 7.6 eV. Evidently, C6H5NH2+ is not produced by dissociative ioni zation of the excited neutral complex. Instead, the complex must first be ionized and excited to at least 0.1 eV. Since the onsets for (C6H5 Cl.NH3)(+) and C6H5NH2+ are lower than for C6H5NH3+, then (C(6)H5(C)l. NH3)(+) in its ground state does not spontaneously form C6H5NH3+. Kine tic energy release distributions measured for C6H5NH2+ and C6H5NH3+ in dicate 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.