Precision measurements of electric-field 1snℓ singlet-triplet anticrossings of HeIusing radio frequency spectroscopy

Abstract

The energy separations of closest approach were measured for the 1sn 1 × 3 anticrossings of singlet and triplet Stark states of the 1s4d, 1s5d and 1s5f configurations of He I. Using a fast atomic He beam, a selective population of the upper state of the anticrossing was accomplished by starting with an initial selective excitation of singlet states by 12 keV He-He collisions followed by an adiabatic transit to the electric field of the anticrossing, where radiofrequency transitions were induced. From the resonance signals the energy separations of three 1s4d, four 1s5d and three 1s5f anticrossings were determined. We evaluated the off-diagonal matrix elements of the spin-orbit coupling for the 1s4 and 1s5 configurations from the measured energy separations. The experimental results are compared with the calculated values.

Electric-field-induced redistribution of radiation transition probabilities in atomic multiplet lines

“…is the field-dependent splitting between the two states, which turns into the fine-structure splitting when the field F 0 vanishes, (0) = δ. The lowest order (second order) in perturbation V energy shift in the external field for the non-degenerate substate with M = ±J max = L + S is E (2) = W (2) L+S L+S = −…”

“…We confine our further considerations to the field region F 0 ≈ F A , with account of only second-order terms. If in calculating radial matrix elements we neglect the multiplet splitting in comparison with the energy separation between multiplets with different principal n and/or orbital L quantum numbers, then the second-order approximation to the matrix elements (3), W (2) J J = F 2 0 w J J , may also be written in terms of scalar and tensor polarizabilities [6]:…”

“…The calculated values demonstrate their asymptotic behaviour α s,t nL = C s,t L ν 7 for highly excited Rydberg states with As follows from the data for polarizabilities of table 1 and for fine-structure splitting [18], the anticrossing effect cannot appear in triplet D-states of helium, except for the 3 3 D-state with positive value of tensor polarizability and anticrossing field of F A = 20.524 kV cm −1 for states with M = 0, J 1 = 3, J 2 = 1 (see equation ( 17)) or F A = 3.567 kV cm −1 for states with |M| = 2, J 1 = 3, J 2 = 2, according to equation (25). In all n 3 P-states of helium, including Rydberg states with very high n, the anticrossing effect may appear and has been discussed in detail in [1][2][3][4][5][6][7].…”

“…The most important results in this area during the last decade have been obtained for helium triplet states, both experimentally [1][2][3] and theoretically [5][6][7]. Together with field-induced variation of energy structure of atomic levels, the reconstruction of wavefunctions in atomic multiplets has been studied, which may cause essential changes in radiation matrix elements and transition probabilities.…”

Electric-field singlet-triplet anticrossings of the 1snd configurations of 3He atoms

“…The singlet-triplet anticrossings of 4 He-1snd configurations have been studied in recent years, both theoretically [1] and experimentally [2][3][4][5][6]. By measuring the energy separations at these anticrossings, the off-diagonal matrix elements of the spin-orbit coupling could be determined [2,3], and by analysing the amplitudes of anticrossing signals, the charge distributions of collisionally excited He I states could be deduced [4][5][6].…”