ЕЛЕКТРОННЕ ЗБУДЖЕННЯ КВАЗІМЕТАСТАБІЛЬНОГО СТАНУ (4p55s5p)4S3/2 АТОМА РУБІДІЮ

Abstract

Експериментально досліджено електронне збудження квазіметастабільного стану (4p55s5p)4S3/2 атома рубідію в діапазоні енергій зіткнень від порогу до 19 еВ. Функ-ція збудження, яка одержана при моноенергетичності електронного пучка 0.12 еВ, вказує на наявність припорогових резонансів негативного іона рубідію. Здійснено порівняння з експериментальними та теоретичними перерізами збудження кварте-тного автоіонізаційного стану (4p54d5s)4P1/2 атома рубідію та квазіметастабільного стану (3p54s4p)4S3/2 атома калію. Максимальне значення перерізу збудження стану (4p55s5p)4S3/2 складає σ=3.77×10-18 см2. Ключові слова: атом, збудження, рубідій, квазіметастабільний стан.

Background: Among the metals, the alkali atoms possess the simplest electronic structure of their outer shells, consisting of one valence electron and a filled subvalent shell. This makes them a favorite test object for experimental and theoretical studies of different ex-citation and ionization processes. An important role of resonance processes in excitation of the 4p5n1l1n2l2 autoionizing states in Rb atoms is expected from the evident resonance character of the autoionization contribution to the total ionization cross section and from the sharp rise of the excitation cross section close to the excitation thresholds of the lowest metastable and quasi-metastable autoionizing states. In the present work we consider the electron-impact excitation function of the (4p55s5p)4S3/2 state in Rb atom. By comparing with other data we analyze the excitation processes forming the shape of excitation func-tion at near-threshold impact energies. Methods: The measurements were carried out using an ejected-electron spectrometer con-sisting of a monochromator and an analyzer for electrons (both of 127◦ electrostatic type) and an atomic beam source. Sets of spectra were processed by subtracting the background intensity in deriving the line intensities. The ejected-electron excitation function of the (4p55s5p)4S3/2 state was obtained as an incident-electron energy dependence of the corre-sponding line intensity. The cumulative relative uncertainty of the excitation cross section is estimated to be 40%. Results: The ejected-electron excitation function for the (4p55s5p)4S3/2 state was studied in an impact energy region from the excitation threshold up to 3 eV above it. The excitation function shows small sharp resonance just above the threshold and a broad resonance lying about 1.5 eV above it with a “fine structure” k-n. The wide, asymmetric shape of these features suggests the combined effect of several overlapping resonances which are typical for excitation of the subvalence shells in heavy alkali atoms. A comparison of the excita-tion function was made with the excitation functions of the close-lying (4p55s5p)4P1/2 state and (3p54s4p)4S3/2 quasimetastable state in potassium. The cross section reaches its maxi-mum value of 3.77x 10-18 cm2. Conclusions: The total excitation cross section of the 4p54s4p 4S3/2 quasimetastable level in rubidium has been investigated experimentally for incident electron energies up to 3 eV above the excitation threshold. In the experimental energy dependence of the cross section a complicated structure was found due to core-excited Rb− resonances. PACS NUMBER: 34.80.DP