Werner J. Pietsch

Structure effects seen in the dissociation of 3.5-MeV beams of CO+2 and N2O+ in thin foils☆

Abstract We show examples of energy spectra obtained for ionic fragments that are emitted in the forward direction when 3.5-MeV beams of CO + 2 and N 2 O + dissociate in thin (≈ 150 A) carbon foils. The spectra demonstrate in a novel way the structures of the two species of incident molecular ions.

Experimental confirmation of the Jahn–Teller distortion of CH4+

We report measured energy and angular distributions for H+ and Cn+ (n=2,3,4) fragments resulting from the collisional dissociation of 194 keV/amu Chn+ (n=0–4) in thin carbon foils. From the systematic trends of these ’’Coulomb explosion’’ spectra, one can obtain qualitative information on the structures of these species. In particular, the series displays a narrowing of the carbon angular and energy widths as protons are symmetrically added around a central carbon atom and provide a ’’focusing’’ effect. Because of the Jahn–Teller distortion, the widths measured for CH4+ are dramatically increased. (AIP)

Measurement of the distributions of internuclear separations in 3.0 MeV H2+ and 3.63 MeV HeH+ beams☆

Abstract Angular distributions of charged dissociation fragments are measured for 3.0 MeV H2+ and 3.63 MeV HeH+ ions incident on ∼ 160 A carbon targets. By using the reflection method for a pure Coulomb potential we unfold from these data the distributions of internuclear separations for each molecular-ion species prior to dissociation. These results are insensitive to ion-source conditions. For H2+ this distribution, while ∼2 times wider than a pure ground vibrational state population, is markedly different from the Franck-Condon distribution that has been previously assumed by other authors with similar rf and duo-plasmatron ion sources. For HeH+ the distribution is slightly broader (∼1.5 times) than that expected for a pure ground state population. From the data, we are able to extract the initial vibrational state population in the incident beam.

The transmission of fast molecular ions through thin foils

Abstract We present new results on the transmission of fast molecular ions through thin foils and propose a mechanism for the transmission process. The main feature of the postulated mechanism is that a finite fraction of the incident molecular beam does not undergo a strong Coulomb explosion while traversing the foil. Because the emerging fragments are at large internuclear separations, there is an enhanced probability for the formation of bound, long-range, excited electronic states following electron capture at the rear surface of the target.

Erratum: Experimental confirmation of the Jahn–Teller distortion of CH4+ [J. Chem. Phys. 72, 1402 (1980)]

We report measured energy and angular distributions for H+ and Cn+ (n=2,3,4) fragments resulting from the collisional dissociation of 194 keV/amu CHn+ (n=0–4) in thin carbon foils. From the systematic trends of these ’’Coulomb explosion’’ spectra, one can obtain qualitative information on the structures of these species. In particular, the series displays a narrowing of the carbon angular and energy widths as protons are symmetrically added around a central carbon atom and provide a ’’focusing’’ effect. Because of the Jahn–Teller distortion, the widths measured for CH4+ are dramatically increased.

Neutral hydrogen from the foil-induced dissociation of 4HeH+, 3HeH+, and H2+

Abstract High-resolution energy spectra and angular distributions of H 0 from the dissociation of 4 HeH + , 3 HeH + , and H 2 + in thin carbon foils are presented for incident ion energies ranging from 170 to 1800 keV/amu. For the range of dwell times inside the target foils studied (about 1–10 fs), the dominant mechanism for such dissociation is the Coulomb explosion of the ions inside the target followed by electron capture near the rear surface of the foil. At the shortest of these dwell times, the yield of H 0 for incident ions oriented perpendicular to the beam relative to that for ions aligned with the beam is a factor of two greater than at longer dwell times. These data indicate that, for ion fragments which emerge from the rear surface of the target within a few A of one another, those in the perpendicular orientation have a greater electron capture probability than those emerging in other orientations.

Experimental confirmation of the Jahn-Teller distortion of CH4+

Abstract We report measured energy and angular distributions for H + and C n + ( n = 2, 3, 4) fragments resulting from the collisional dissociation of 200 keV/amu CH m + ( m = 0−4) in thin carbon targets. From the systematic trends of these “Coulomb explosion” spectra, one can obtain qualitative information on the structures of these species. In particular, the series displays a narrowing of the carbon angular and energy widths as protons are symmetrically added around a central carbon atom and provide a “focusing” effect. Because of the Jahn-Teller distortion, the carbon width in CH 4 + is dramatically increased.