Adam C. R. Wilkins

Translational energy spectroscopy of single-electron capture by C2+ ions in He, Ne and Ar

Abstract High resolution (0.3 eV at FWHM) translational energy spectroscopy has been employed to study single-electron capture by 4 keV C 2+ ions in collision with He, Ne and Ar atoms. Our results are generally in good agreement with previous measurements. Our spectra reveal an additional weak channel for C 2+ in He and two additional weak channels for C 2+ in Ne, not previously reported. One of these capture channels in Ne occurs at a relatively large endothermic energy change. Eight transitions are identified for the single-electron capture by C 2+ in Ar.

Single electron capture by C3+ ions in He, Ne and Ar

Abstract Translational energy spectra have been obtained for 6 keV C 2+ ions resulting from single-electron capture by 6 keV C 3+ ions in collision with He, Ne and Ar. Our data for He and Ne are in good agreement with previous measurements, while data for the Ar target have not appeared in the literature. The spectrum for C 3+ in Ar is complex and appears to contain many strong spectral features which involve capture with excitation of the target product ion in Ar + .

Variation in isomeric products of a phosphodiesterase from the chloroplasts of Phaseolus vulgaris in response to cations

ABSTRACT Fast-atom bombardment mass spectrometry (FABMS), and collisionally-induced dissociation and mass-analyzed ion kinetic energy spectrum scanning (CID/MIKES) have been used to examine cation effects on a Phaseolus chloroplast complex phosphodiesterase activity. The kinetic parameters of the activity, and the effects of Li+, Na+, K+, Mg2+, Mn2+ and Fe3+ upon them, were determined with 3′,5′-cyclic AMP, -GMP and -CMP, and 2′,3′-cyclic AMP, -GMP and -CMP as substrates. Irrespective of the presence of cations and of the complex nucleotidase, the preferred substrate is a 3′,5′-cyclic nucleotide, not a 2′,3′-cyclic nucleotide. In the presence of the nucleotidase 3′,5′-cyclic AMP and 3′,5′-cyclic GMP are the best substrates, unless Fe3+ ions are present. Mg2+ and Mn2+ stimulate hydrolysis of 3′,5′-cyclic AMP and 3′,5′-cyclic GMP by the complex. However, Fe3+ inhibits these activities but stimulates the hydrolysis of 3′,5′-cyclic CMP. Kinetic data indicate that each of these six substrates is hydrolyzed at a single, common, catalytic site. Differentiation of the phosphodiesterase isomeric mononucleotide products by FABMS CID/MIKES analysis indicates that in the absence of ions and after removal of the nucleotidase, the 3′-ester linkage of the 3′,5′-cyclic substrates was hydrolyzed exclusively. Addition of monovalent and divalent ions results in hydrolysis of both the 5′- and 3′-ester linkages.

State selective double-electron capture processes by Xe3+ and Kr3+

High resolution double-electron capture translational energy-loss spectra have been obtained for Kr3+ in Ar and Xe3+ in Ar and Kr at a collision energy of 6 keV. For the Kr3+ in Ar spectrum the transitions are assigned to excited states in both the projectile and target ions. The Xe3+ in Ar spectrum displays eight well resolved peaks which are attributed to four reaction channels and their corresponding spin-orbit coupling states. The spectrum for Xe3+ in Kr is remarkably similar, however the reaction channels are formed from capture into higher excited states of the target ion confined by energetic and adiabatic potential energy curve crossing parameters.

Single electron capture by B2+ ions in Ne, Ar, Kr and Xe

Abstract High resolution translational energy spectra have been obtained for state-selective single-electron capture by 8 keV B2+ in Ne, Ar, Kr and Xe. The Ne spectrum is used to determine accurately the zero energy change position for subsequent analysis of the three other systems. Six capture channels have been unambiguously identified for Ar, all producing Ar+ in the ground [3p5 2P0] state. Kr exhibited eight capture channels and Xe seven, with both systems exhibiting spin-orbit splitting of the 2 P 3 2 , 1 2 state, Kr+ being split by 0.67 eV and Xe+ by 1.3 eV. The Kr+ spectrum is neatly ordered into four well separated doublet peaks, whereas the relationship between doublets for Xe+ is less obvious. Using a statistical model to compare the expected populations of the spin-orbit states of Kr+ and Xe+ to the observed populations, a novel method for calculating the gradient of the reaction window for systems which exhibit spin-orbit splitting has been developed. By comparing partial cross section data from all collision systems under study the results were found to be in good agreement with the Landau-Zener curve-crossing model.

Spin violation in double-electron capture by Ar4+ ions

Abstract Translational energy spectroscopy has been employed to study state-selective double-electron capture by 8 keV Ar 4+ in He and Ne targets, and 12 keV Ar 4+ in He. The capture spectra are dominated by reaction channels which violate spin conservation. The double capture spectra for Ar 4+ in He contain intense peaks which involve capture from the metastable quintet 5 S 0 state of Ar 4+ , recently identified in single capture spectra for Ar 4+ in He and Ne.

Two-electron capture by C3+ ions: competition between single and double electron processes

Abstract State-selective translational energy spectroscopy has been used to study two-electron capture processes for 6 keV C3+ ions in collision with He, Ne and Ar atoms. The spectrum for the formation of C+ from the He target reveals only features resulting from double-collision single-electron capture processes while the spectrum for C+ from the Ne target reveals both single-collision double-electron capture and double-collision successive single-electron capture processes. The spectrum for the Ar target consists entirely of double-electron capture channels in which the target product Ar2+ ion is left in the ground state with some indication of double capture into autoionizing states of the C+ ion.