Paul-trap resonance in He + –He collisions

The anticrossing spectra of the helium line λ(1s4l-1s2p 3 P) = 447.2 nm were measured for 10-30 keV He + -He collisions. The theoretical intensity functions were calculated taking into account cascade processes, the inhomogeneity of the axial electric field in the collision volume and the density distribution of the target He atoms. Comparing the theoretical intensities with the measured ones, the post-collisional states of He atoms were determined. The results indicate that for this projectile-energy range, the electronic charge distributions of the excited-atom states change from almost symmetric to strongly asymmetric ones with large electric dipole moments. This result suggests that for projectile energies of 20-30 keV, Paul-trap promotion becomes the main excitation mechanism.

Section: Introductionmentioning

confidence: 81%

“…Recent investigations [8][9][10] have shown that not only the resonance-like structure of the excitation function is characteristic for the intermediate energy range of these He + -He collisions, but also large electric dipole moments (EDMs) [11] and other data are taken from [12].) of the collisionally excited states.…”

Section: Introductionmentioning

confidence: 99%

Excitation of He atoms by 10–30 keV He⁺impact

Baszanowska

Drozdowski

Kamiński

et al. 2012

“…For measuring the fluorescence-light intensity of the line λ (1s5l 3 D-1s2p 3 P) ≈ 402 nm of helium atoms excited by He +ion impact, the experimental set-up described in [9,11,30] and in [13] was used. The ion beam was extracted from a Penning ion source and focussed on the collision chamber using two electrostatic lenses.…”

Section: Experimental Set-upmentioning

confidence: 99%

“…Due to the conservation of the total electron spin in atomic collisions, only singlet states of He atoms are excited. Since singlet and triplet states are strongly mixed at the electric field strengths of singlet-triplet anticrossings [9,10], significant resonance-like intensity variations at these anticrossings can be detected. In particular, the amplitudes of these anticrossing resonances allow a detailed investigation of the excitation parameters of impact-excited He atoms.…”

Section: Introductionmentioning

confidence: 99%

“…With the use of anticrossing spectroscopy, it has been shown that the impact-excited atoms have almost maximal EDMs after collisions at intermediate energies, where the relative velocity of the collision partners is of the order of the Bohr velocity of the bound electrons. This phenomenon has been explained with the Paul-trap mechanism, in which an electron is transiently trapped during the collision on the saddle of the two-centre Coulomb-potential of the collision partners [9,[14][15][16][17][18]. Both the target atoms' EDMs and those of the projectile atoms produced by transfer and excitation have been detected [19].…”

Section: Introductionmentioning

confidence: 99%

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Electric dipole moments of He atoms excited to the 1s5l(l⩾ 2) states by He⁺-ion impact at intermediate energies

Baszanowska¹,

Drozdowski²,

Kamiński³

et al. 2014

Self Cite

The post-collisional 1s5l (l ⩾ 2) states of He atoms after He+-ion impact (10 keV–28 keV) have been investigated using anticrossing spectroscopy. In particular, the intensity of the spectral line λ(1s5l 3D-1s2p 3P) = 402.6 nm emitted by the impact-excited He atoms was measured as a function of an axial electric field (which varied from −30 kV cm−1 to +30 kV cm−1). By fitting the theoretical intensity functions to the measured ones, the post-collisional states of the atoms and their electric dipole moments were determined. The results indicate that for projectile energies below 20 keV, the electric dipole moments are small; however, for energies above 20 keV, mainly the parabolic Stark states with maximal electric dipole moments are excited. We conclude that in the upper section of the energy range investigated here, the Paul-trap promotion is the dominant excitation mechanism for He+–He collisions.

Anticrossing spectroscopy of He atoms excited by 30–300 keV He⁺impact

Busch¹,

Drozdowski²,

Ludwig³

et al. 2004

Self Cite

By measuring the anticrossing spectra of the 1s4 and 1s5 He I levels, we investigate single-electron excitation in 30-300 keV He + -He collisions. The post-collisional He I states are highly coherent superpositions of spherical states with large electric dipole moments. These superposition states vary gradually with the impact energy from purely parabolic states at 30 keV to superpositions of 2 states at 300 keV. The results indicate that for the whole energy range single-electron excitation should be considered as a process mainly localized in the saddle region of the two-centre Coulomb potential of the (He + ) 2 molecular core. A theoretical model based on the symmetry of the collision system is discussed.