INTERFERENCE EFFECTS IN ELECTRON EMISSION SPECTRA

M. WINKWORTH; P.D. FAINSTEIN; M.E. GALASSI; J. BARAN; B.S. DASSANAYAKE; S. DAS; T. ELKAFRAWY; D. CASSIDY; J.A. TANIS

Tokyo, Japon

Conferencia; 14th International Conference on the Physics of Highly Charged Ions (HCI); 2008

In recent studies electron interference effects have been studied for H+ + H2 [1] and H+ + N2 [2] collisions. Both primary interference structures analogous to Young’s two slit experiment as well as secondary interferences attributed to intramolecular scattering have been observed [1]. The primary interferences observed in 1-5-MeV/u H+ + H2 collisions [1] showed a strong dependence on the electron observation angle and a smaller dependence on the projectile velocity, while the secondorder interferences superimposed on the main oscillatory structures were independent of angle and velocity. More recent results for H+ + N2 at similar projectile energies revealed apparently only secondary oscillations [2]. In the present work, the experimental investigations are extended to 3MeV H+ + O2. As a result of the larger “slit” separation for O2 of 2.28 a.u., compared with 2.1 a.u. for N2 and 1.4 a.u. for H2, the primary interference structures would be expected to have higher frequencies. Experimental measurements were conducted at Western Michigan University using the tandem Van de Graaff accelerator. A collimated proton beam interacted with an O2 target supplied by a gas jet. Emitted electrons were detected with a parallel-plate analyzer equipped with a channel electron multiplier for observation angles of 30º, 60°, 90º and 150° with respect to the incident beam direction and for ejected electron energies of 5-400 eV. The measured molecular O2 cross sections were normalized to corresponding theoretical O2 cross sections calculated using one-center wave functions. Ratios of the measured experimental to theoretical cross-sections for each angle were fit with a sinusoidal function f(k) = A[sin(kcd–w)]+B as shown in Fig. 1, where c is a frequency fitting parameter and w allows for a phase shift. Notably, the frequencies of the oscillatory structures are independent of the observation angle while the phase shifts seem to vary systematically with angle, qualitatively in agreement with results for H+ + N2 [2]. The analysis gives an oscillation interval for O2 of Dk ~ 4 a.u., while for N2 a value of Dk ~ 2 a.u. was found. The independence of the oscillation frequency on the observation angle suggests the structures are due to secondary interferences with no obvious evidence for primary interferences. However, this conclusion needs further theoretical and experimental investigation. [1] S. Hossain et al., Phys. Rev. A 72 (2005) 010701(R) [2] J.L. Baran et al., J. Phys.: Conf. Ser. 58 (2007) 215