Electron impact excitation of the Tl ⁺ ion: resonance and cascade transitions

Abstract

Results of experimental and theoretical investigations of electron-impact excitation of the resonance 6s6p (_ ^1)P_1^°  6s2 1S0 (132.2 nm) as well as the cascade 6s7s 1S0  6s6p (_ ^1)P_1^° (309.2 nm) and 6p2 1D2  6s6p (_ ^1)P_1^° (150.8 nm) spectral transitions from the ground 6s2 1S0 level in the thallium ion are presented. Crossed beams of electrons and Tl+ ions in combination with a spectroscopic method were used in the experiment. Measured cross-sections have a distinct resonance structure arising mainly from the electron decay of atomic 5d96s26p2, 5d106s7s(1S)np (n≥7), 5d106s6d(1D)np (n≥6), 5d106s6d(1D)nd (n≥6) and ionic 5d96s2np, 5d96s2nd, 5d96snp (n6) autoionizing levels as well as radiative transitions from the higher 6s7s 1S0, 6s6d 1D2, and 6p2 1D2, 1S0 ionic levels. Relativistic distorted wave (RDW) calculations are performed to obtain the effective cross-sections for the above transitions. The absolute values of the cross-sections are found to be 1.3910–16 cm2 at 300 eV for the 132.2 nm resonance line, 0.1110–16 cm2 and 0.5610–16 cm2 at 100 eV for the 309.2 nm and 150.8 nm lines, respectively. The contribution of the cascade transitions under study to the effective cross section of the 132.2 nm resonance line at the energy of 100 eV is about 30%. Calculation using the semi-empirical Van Regemorter formula is also performed to obtain the effective cross-section of the resonance 132.2 nm line. The absolute value of the cross-section at 300 eV is found to be nearly the same as given by the RDW calculation.