A. Bolovinos

3dnl J=0e-2e autoionizing levels of calcium: observation by laser optogalvanic spectroscopy and theoretical analysis

The even parityJ=3 autoionizing spectra of calcium were investigated below the 3d threshold by a two-step laser excitation from the 3d4s metastables through the 3d4p3P2,1F3 intermediate states. The 3d4s were populated by electronic collisions in a d.c. glow dis-charge through a Ca heat-pipe. More than a hundred resonance transitions have been measured with an accuracy of ∼0.2 cm−1 for the narrow ones using standard laser calibration techniques. Their upper levels are assigned to all expected nine autoionizing 3dns, 3dnd and 3dng Rydberg series and the 4p 5p3D3 perturber. The theoretical interpretation is achieved by a combination of the eigenchannelR-matrix and mulitchannel quantum defect (MQDT) methods. Ten closed and two openJ=3 interacting channesl are used. Theoretical energy level positions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixing between the 3d3/2nd5/2 and 3d5/2nd3/2 series is found, while the 3d3/2nd3/2 and 3d5/2nd5/2 series are almost purejj-coupled. The calculations were particularly successful in reproducing the spectrum in the region of the 4p 5p3D3 perturber, where strong chancel mixing appears leading to interference effects in the excitation cross sections.

3dnl J=3e autoionizing levels of calcium: observation by laser optogalvanic spectroscopy and theoretical analysis

The even parityJ=3 autoionizing spectra of calcium were investigated below the 3d threshold by a two-step laser excitation from the 3d4s metastables through the 3d4p3P2,1F3 intermediate states. The 3d4s were populated by electronic collisions in a d.c. glow dis-charge through a Ca heat-pipe. More than a hundred resonance transitions have been measured with an accuracy of ∼0.2 cm−1 for the narrow ones using standard laser calibration techniques. Their upper levels are assigned to all expected nine autoionizing 3dns, 3dnd and 3dng Rydberg series and the 4p 5p3D3 perturber. The theoretical interpretation is achieved by a combination of the eigenchannelR-matrix and mulitchannel quantum defect (MQDT) methods. Ten closed and two openJ=3 interacting channesl are used. Theoretical energy level positions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixing between the 3d3/2nd5/2 and 3d5/2nd3/2 series is found, while the 3d3/2nd3/2 and 3d5/2nd5/2 series are almost purejj-coupled. The calculations were particularly successful in reproducing the spectrum in the region of the 4p 5p3D3 perturber, where strong chancel mixing appears leading to interference effects in the excitation cross sections.

Detection of the even parity,J=0–3, autoionizing 4dnl Rydberg states of strontium by two-step laser optogalvanic spectroscopy

We have measured the energies of a few hundreds of even parity,J=0–3 autoionizing 4dnl Ry states of strontium using an optogalvanic spectroscopy technique. These states are reached by a two-step pulsed dye laser excitation from the 4d 5s metastables through the 4d 5p3P0,1,2 intermediate states. Electronic collisions populate the 4d 5s states in a d.c. glow discharge through a Sr plus He vapour in a heated quartz cell. The electronic configuration for the majority of the observed Sr states is deduced from their quantum defect values and other characteristics of the corresponding transitions.

Two-step laser optogalvanic spectroscopy of highJ momentum 4dnd and 4dng autoionizing states of strontium

We have measured the energies of about two hundred even parityJ=3–5 autoionizing 4dnd and 4dng Rydberg states of strontium (Sr) using an optogalvanic method. These states are reached by a two-step dye laser excitation from the 4d5s metastables through the 4d5p3P2,1F3,3F4 intermediates. The 4d5s are populated in a d.c. glow discharge through a Sr heated cell. The electronic configuration of the observedJ=3, 4 states is deduced from the Lu-Fano plots of their quantum defect values and the spectral characteristics of the corresponding transitions.

Two-photon ionization spectra of calcium above the 4s1/2 threshold

Two-photon ionization of ground state calcium is investigated both experimentally and theoretically in the 374–323 nm spectral range. The spectra are dominated by the presence of the 4p2 1S0 perturber and by members of even parity 3dnd J = 0, 2 (4 ≤ n ≤ 10) and 3dns J = 2 (6 ≤ n ≤ 12) autoionizing Rydberg series, the latter appearing as window resonances. No single-photon resonances are observed. The majority of recorded lines are identified using older stepwise spectroscopic data while there is a number of newly discovered low-lying members. The two previously unobserved 3dns, n ≤ 12, series members are treated using a semi-empirical multichannel quantum defect theory (MQDT) model. Moreover, the low-lying part of the observed predominantly singlet spectrum is fairly well reproduced by theoretical calculations, combining a configuration interaction approach with B-splines basis functions and neglecting relativistic effects. The agreement between theory and experiment becomes less satisfactory as we move towards higher lying resonances dominated by singlet–triplet mixing effects, which are evident in the experimental data while neglected in the calculations.