Structure and fragmentation of doubly ionized HNCS.

Double ionization spectra of isothiocyanic acid (HNCS) have been measured using multi-electron and multi-ion coincidence techniques combined with high-level theoretical calculations. The adiabatic double ionization energy of HNCS is found at 27.1 ± 0.1 eV and is associated with the formation of the X 3A″ ground state of HNCS2+. The characteristics of different dissociation channels are examined and compared to the results of electronic structure calculations obtained by systematically elongating the three bonds H-NCS, HN-CS, and HNC-S. For instance, the adiabatic double ionization energy of the NCS fragment is deduced to be 30.95 ± 0.5 eV. In addition, the C+ and NS+ dissociation channels are of particular interest, possibly indicating the involvement of a structural rearrangement process upon doubly ionizing HNCS.

Double Photoionization of Nitrosyl Chloride by Synchrotron Radiation in the 24-70 eV Photon Energy Range.

The behavior of nitrosyl chloride (ClNO) exposed to ionizing radiation was studied by direct probing valence-shell electrons in temporal coincidence with ions originating from the fragmentation process of the transient ClNO2+. Such a molecular dication was produced by double photoionization with synchrotron radiation in the 24-70 eV photon energy range. The experiment has been conducted at the Elettra Synchrotron Facility of Basovizza (Trieste, Italy) using a light beam linearly polarized with the direction of the polarization vector parallel to the ClNO molecular beam axis. ClNO molecules crossing the photon beam at right angles in the scattering region are generated by effusive expansion and randomly oriented. The threshold energy for the double ionization of ClNO (30.1 ± 0.1 eV) and six dissociation channels producing NO+/Cl+, N+/Cl+, N+/O+, O+/Cl+, ClN+/O+, NO+/Cl2+ ion pairs, with their relative abundance and threshold energies, have been measured.

Basic features of Ne*-HX (X = Cl, Br) chemi-ionization reactions.

Total and partial ionization cross sections for Ne*(3P2,0)-HX (X = Cl, Br) are presented in a comparative way as a function of the collision energy between 0.02-0.5 eV. New mass spectrometric data on Ne*-HBr chemi-ionization are discussed and analyzed with already published data on Ne*-HCl, highlighting similarities and differences of the collisional stereodynamics of the two systems. Basic features of the interaction potentials, driving reactive collisions, suggest that reaction channels, leading to the formation of parent HX+ ions in the ground and excited electronic state and to the formation of associated NeHX+ ions as well as of NeH+ proton transfer species, are selectively opened within angular cones exhibiting different orientation and acceptance.