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Oscillatory behavior and trajectory dependent effects in the population of helium(3 phosphorus-3) and helium(3 phosphorus-1) in single positive helium ion - hydrogen-2, helium-deuteride and positively charged dihydrogen - helium collisions
Abstract
To investigate a simple triatomic system, various measurements were performed to elucidate the excitation mechanisms of the (He-H$\sb2$/D$\sb2$)$\sp+$ quasimolecule. These include total cross section measurements of the magnetic substates of the He(3$\sp3$P) level populated in He$\sp+$-H$\sb2$, He$\sp+$-D$\sb2$ and He$\sb2\sp{+}$-He collisions and the He(3$\sp1$P) level populated in He$\sp+$-H$\sb2$ and He$\sp+$-D$\sb2$ collisions. The cross sections show an oscillatory behavior which suggests that there are long range interactions of the quasimolecular states (Rosenthal oscillations). The nature of the oscillatory structure is dependent upon the details of the potential curves of the (He-H$\sb2$/D$\sb2$)$\sp+$ complex. Use of the quasidiatomic model allows construction of diabatic states that enable the identification of the dominant excitation channels. In addition to oscillatory structure, the m$\sb1$ = $\pm$1 cross sections exhibit an isotope shift both in relative velocity dependence and in the magnitude of the cross section for population of He(3$\sp1$P) and He(3$\sp3$P) in He$\sp+$-H$\sb2$/D$\sb2$ collisions. Similar shifts are predicted by theories of rotational coupling in ion-atom collisions and result from differences in the projectile trajectories for the different target masses. The shift in relative velocity dependence which we observe is smaller than expected for ion-atom collisions. Extension of the ideas inherent in ion-atom rotational coupling to those of ion-molecule collisions enables interpretation of the smaller shift as being the result of a diffuse molecular target. To further test whether the observed isotope shift is the result of rotational coupling, a series of coincidence measurements were conducted on the He$\sp+$-H$\sb2$/D$\sb2$ collision system in which the scattered neutral He was measured in coincidence with the polarized 3889 A radiation from the He(3$\sp3$P $\to$ 2$\sp3$S) transition. By using the appropriate scaled projectile velocities as found in the total cross section measurements, comparisons of results obtained for He$\sp+$-H$\sb2$ collisions were made with He$\sp+$-D$\sb2$ collisions. This ensures similar projectile trajectories and hence similar probabilities of rotational coupling. Recognition of the isotope shift as a signature of rotational coupling permits identification of the dominant quasimolecular excitation mechanisms.
Subject Area
Atoms & subatomic particles
Recommended Citation
Engelhardt, Cathy Lynne, "Oscillatory behavior and trajectory dependent effects in the population of helium(3 phosphorus-3) and helium(3 phosphorus-1) in single positive helium ion - hydrogen-2, helium-deuteride and positively charged dihydrogen - helium collisions" (1987). ETD collection for University of Nebraska-Lincoln. AAI8803748.
https://digitalcommons.unl.edu/dissertations/AAI8803748