The post-collision energy shift of the (np⁵(n+ 1)s²)²P_3/2lines in autoionizing spectra of sodium (n= 2) and caesium (n= 5) atoms excited by electron impact

Abstract

The energy shift of lines arising from the decay of the (np5(n + 1)s2)2P3/2 autoionizing states in Na (n = 2) and Cs (n = 5) atoms has been studied for the first time in ejected-electron spectra measured over the excess energy range −0.1 to 5.4 eV. In Na spectra, the energy dependence of the shift possesses a clear oscillatory-like character. In particular, the shift becomes of negative or positive sign depending on the presence or absence of a negative-ion resonance structure in the excitation function of the (2p53s2)2P3/2 state. Earlier, we reported a similar behaviour of the line shift for the (3p54s2)2P3/2 autoionizing state in K atoms. Though in Cs atoms the strong negative-ion resonance is also present close to the excitation threshold of the (5p56s2)2P3/2 state, in contrast to Na and K data, the energy dependence of the line shift possesses a smooth asymptotic behaviour described well by the classical model of the post-collision effect. The comparative analysis of the spectroscopic classification of the resonance structure in the excitation of the (np5(n + 1)s2)2P3/2 autoionizing states in Na, K and Cs atoms has shown that the observed effect most probably reflects the complication of the compound character of resonances. In whole, the obtained data show that under the condition of the high polarizability of a resonantly excited target the relation between polarization attraction, centrifugal and Coulomb repulsion becomes a crucial factor which determines the final energy distribution of outgoing electrons.

The post-collision interaction effect in autoionizing spectra of alkali atoms excited by electron impact

“…In particular, instead of the smooth asymptotic behaviour, the line shift in ejectedelectron spectra reveals both positive and negative signs depending on the presence/absence of resonances in excitation functions of the lowest p 5 s 2 autoionizing states. In contrast to these data, the energy dependence of the line shift for the (5p 5 6s 2 ) 2 P 3/2 autoionizing state in heavier caesium possesses a simple asymptotic character [10]. This was tentatively explained by the more complicated compound character of the resonance structure observed in the excitation function of this state.…”

“…Meanwhile, the influence of polarizability and resonance processes on the correlated interaction of two outgoing electrons was supposed in the first studies of the PCI effect [7,8]. As shown in our recent data for sodium and potassium [9,10], the high polarizability and dominant role of resonance processes in excitation of the outer p 6 subshell of these atoms influence indeed the dynamics of the PCI process. In particular, instead of the smooth asymptotic behaviour, the line shift in ejectedelectron spectra reveals both positive and negative signs depending on the presence/absence of resonances in excitation functions of the lowest p 5 s 2 autoionizing states.…”

“…In figure 2 the PCI line shift ε and electron impact excitation cross-section σ (normalized to the maximum value) are presented for the (np 5 [n + 1]s 2 ) 2 P 3/2 (a) and 2 P 1/2 (b) autoionizing states in Na (n = 2) [10,20], K (n = 3) [9,12], Rb (n = 4) [11] and Cs (n = 5) [10,13] atoms. There are no PCI data for the 2 P 1/2 states in sodium and caesium atoms and the reason for that is overlapping of corresponding ejectedelectron lines by neighbouring dominant lines (2p 5 3s 2 ) 2 P 3/2 in sodium [20] and (5d 2 ( 3 F)) 4 D 1/2 +(5d( 3 P)6s) 2 P 1/2 in caesium [21] which made the correct determination of the position of the line profiles in ejected-electron spectra at threshold impact energies difficult.…”

Resonance excitation of autoionizing states in alkali atoms by electron impact

“…В останньому випадку, без належного врахування цієї зміни, процедура визначення інтенсивності лінії може виявитись некоректною. Аналіз одержаних електронних спектрів у припороговій області енергій зіткнень виявив існування ефекту ВПЗ для всіх досліджених атомів [28][29][30][31]. Максимальне значення енергетичного зсуву 300 меВ спостерігалось для лінії, що відповідає розпаду найнижчого АІС (1s2s 2 ) 2 S 1/2 в атомі літію [28].…”

“…Максимальне значення енергетичного зсуву 300 меВ спостерігалось для лінії, що відповідає розпаду найнижчого АІС (1s2s 2 ) 2 S 1/2 в атомі літію [28]. Мінімальне значення ВПЗ зсуву 60 меВ було визначено для ліній (2p 5 3s 2 ) 2 P 3/2 , (4p 5 5s 2 ) 2 P 3/2 в спектрах атомів натрію [29] та рубідію [31].…”