АВТОІОНІЗАЦІЯ АТОМА СТРОНЦІЮ ПРИ ЗБУДЖЕННІ 4р6 ОБОЛОНКИ

Abstract

Експериментально, шляхом визначення сумарної інтенсивності ліній в електронних спектрах, що утворюються при розпаді атомних автоіонізаційних станів 4p5n1l1n2l2n3l3, одержано переріз авто-іонізації атома стронцію в діапазоні енергій зіткнень від порогу збудження 4р6 оболонки при 20.98 еВ до 600 еВ. Поведінка перерізу характеризується наявністю резонансної структури у припороговій області енергій 21-30 еВ і широкого максимуму поблизу 100 еВ. Максимальне значення перерізу складає 1.610-16 см2 при 24.8 еВ. Проведено аналіз процесів збудження та розпаду автоіонізаційних станів, які визначають величину і енергетичну залежність одержаного перерізу автоіонізації. Ключові слова: електрон, атом стронцію, оболонка, стан, конфігурація, автоіонізація, поперечний переріз.

Background: Autoionization is an indirect ionization process that significantly increases the total ionization cross section of the atom above the excitation threshold of the corresponding electron shell. For strontium atom, the autoionization contribution to the total ionization cross section by electron impact is more than 16%. Measurements of electron autoionizing spectra in a broad range of impact energies and the determination of their total intensity allow obtaining with an acceptable accuracy not only the absolute value of the autoionization contribution (the autoionization cross section), but also its energy behavior. In this paper, the 4p6 autoionization cross section of strontium atoms is investigated in the impact-energy range from the excitation threshold of the 4p6 shell to 600 eV. Methods: The study of the ejected-electron spectra of strontium atoms were carried out by using an electron spectrometer consisted of a source of the incident electron beam, an electron energy analyzer (of 127 electrostatic type) and an atomic beam source. To minimize the influence of the anisotropy of the angular distribution of ejected electrons, the measurements were carried out at a "magic" observation angle of 54.7. The incident and ejected-electron energy resolutions were about 0.4 eV and 0.07 eV, respectively. The increment step of the incident electron energy was 0.1 eV in the near-threshold energy region. The autoionization cross section of strontium atoms was determined as the normalized total intensities of ejected-electron spectra measured at different impact energies. Results: The autoionization cross sections for 4p6 shell of strontium atoms were determined in an incident-electron energy range from the lowest autoionization thresholds up to 600 eV. The energy behavior of the cross section is characterized by the presence of the strong resonance structure in the threshold region of 21-30 eV and a broad maximum at approximately 100 eV. The cross section reaches its maximum value of 1.610-16 сm2 at 24.8 eV. An analysis is made of the excitation and decay processes of the 4p5n1l1n2l2n3l3 autoionizing states that determine the magnitude and the energy behavior of the measured autoionization cross section. Conclusions: The strong resonant excitation of the levels in 4p54d5s2, 4p54d25s, and 4p55s25p configurations determines the resonant behavior of the measured autoionization cross section at low impact energies. The shape and magnitude of the cross section at high impact energies are determined by the total contribution from dipole-allowed and singlets autoionizing levels in the configurations 4p54d5s2, 4p54d25s. Key words: electron, strontium atom, shell, state, configuration, autoionization, cross section. PACS NUMBER: 34.80.Dp