D Burns

Absolute cross sections for electron excitation of the second positive bands of nitrogen

Absolute excitation cross sections for the emission of the second positive bands of nitrogen under electron impact have been obtained. Peak level cross sections for the νprime = 0, 1, 2 levels of the c 3IIu state were found to be, respectively, 235 × 10-18 cm2, 144 × 10-18 cm2 and 49 × 10-18 cm2. Good agreement is found with the theoretical A coefficients for the relative intensities of the different vibrational bands. The results are compared with those of other workers and various secondary effects which were observed are discussed.

Absolute cross sections for ionization and excitation of CO2 by electron impact

Absolute cross sections for simultaneous ionization and excitation of CO2 by electron impact have been measured using a crossed-beam technique. The maximum value of the cross section of the B 2Σu+ level is 224 × 10-18 cm2 and that of the A 2capital Sigmau+ level is 744 × 10-18 cm2. Relative cross sections within the vibrational bands are given. The excitation functions are similar in shape to the total ionization function.

State-selective one-electron capture by 4 keV ground state and metastable ions in collisions with and

The technique of double translational energy spectroscopy (DTES) has been used in a recently developed apparatus to study (for the first time) one-electron capture by state-prepared ions in collisions with and molecules. These processes are relevant to astrophysical situations, planetary atmospheres and to the modelling and diagnostics of edge plasmas in current fusion devices. The main collision channels resulting from state-selective electron capture by pure beams of 4 keV ground state and metastable ions have been separately identified and their relative importance determined without any of the ambiguities inherent in TES studies normally carried out with ion beams of unknown metastable content. At the energy considered, only non-dissociative electron capture is observed with collision channels involving capture into the and states together with the formation of and in ground and electronically excited states. Our measurements indicate that some of these molecular ions have significant degrees of vibrational excitation in accord with the Franck - Condon factors for the relevant transitions. Striking differences between the collision channels for ground and metastable ions are observed.

State-selective one-electron capture by ground-state ions in slow collisions with He, Ne and Ar using double translational energy spectroscopy

Double translational energy spectroscopy (DTES) has been used to study state-selective one-electron capture by pure ground-state ions in collisions with He, Ne and Ar at energies within the range 1.75 - 8.0 keV. The main collision channels have been identified and their relative importance has been assessed quantitatively. These measurements avoid the ambiguities inherent in the interpretation of previous TES measurements carried out using primary ion beams containing unknown fractions of metastable ions. In the absence of any detailed theoretical studies, we have calculated Landau - Zener reaction windows for these processes and shown that they accommodate the observed collision channels with limited success.

State-selective one-electron capture from He, Ne and Ar by 4 keV state-prepared ions

A new instrument to carry out double-translational energy spectroscopy (DTES) recently developed in this laboratory has been described in detail. This permits studies of state-selective electron capture by slow state-prepared multiply charged ions using translational energy spectroscopy (TES). The effectiveness and future potential of this approach has been illustrated by studies of one-electron capture in helium, neon and argon by 4 keV beams of pure ground-state and pure metastable ions. In each case the main product channels have been identified by TES and analysed quantitatively without the ambiguities associated with previous measurements which used primary ion beams containing a mixture of ground and metastable species. A simple beam attenuation technique has also been used in conjunction with our state-prepared beams to provide estimates of the ratios of the total one-electron capture cross sections which, in each case, show that is considerably larger than . These ratios have in turn been used to show that the metastable content of ions from the present ECR ion source and sources used in other laboratories can be substantial.

State-selective electron capture by state-prepared ions in collisions with molecular hydrogen

The technique of double translational energy spectroscopy (DTES) has been used to study state-selective electron capture by pure beams of ground state ions for the first time. The main collision channels have been identified and their relative importance assessed in measurements of one-electron capture by ions in collisions with at energies of 1.75, 4, 6 and 8 keV. These new results help to resolve discrepancies and serious ambiguities in the interpretation of previous measurements carried out with beams containing unknown fractions of metastable ions.

The first use of state-prepared beams of in studies of state-selective electron capture collisions

The use of double translational energy spectroscopy has been successfully demonstrated to allow studies of state-selective electron capture with state-prepared primary ions. Excited product channels arising from one-electron capture by ground-state and metastable ions in collisions with argon have been separately identified.

Technique for studies of state-selective electron capture in collisions involving slow state-prepared multiply charged ions

The intense beams from an ECR ion source/accelerator have been utilised in a new apparatus for studies of state-selective electron capture by multiply charged ions in well defined initial states by double translational energy spectroscopy (DTES). This avoids the ambiguities in previous TES studies carried out with beams containing metastable ions. The effectiveness of DTES is demonstrated by studies of one-electron capture at 4 keV by pure beams of 1S ground state and 3P metastable C2+ ions in collisions with H2, He and Ar.

Production of state-prepared beams of multiply charged ions for studies of state-selective electron capture collisions

A new apparatus which utilizes double translational energy spectroscopy (DTES) is described. This allows studies of state-selective electron capture by multiply charged ions in well defined states. This approach avoids the ambiguities inherent in the results of many previous measurements carried out with beams containing metastable ions. The considerable potential of DTES has been illustrated by measurements of one-electron capture by C2+ ions in collision with Ar at 4 keV.

State-selective electron capture by 4 keV state-prepared beams of ground state and metastable C2+ ions

A new apparatus employing double translational energy spectroscopy has been used to study state-selective electron capture by 4 keV beams of pure 1S ground state and pure 3P metastable C2+ ions in collisions with He and H2. In each case the main excited product channels have been unambiguously identified and their relative importance established.