Autoionizing Rydberg series(np′,nf′)of Ar investigated by stepwise excitations with lasers and synchrotron radiation

Abstract

Synchrotron radiation is used to excite Ar to the intermediate states 3p 1/2 5 ͑3dЈ͓3 / 2͔ 1 , 5dЈ͓3 / 2͔ 1 , 5sЈ͓1 / 2͔ 1 , 7sЈ͓1 / 2͔ 1 ͒ and 3p 3/2 5 ͑6d͓1 / 2͔ 1 , 6d͓3 / 2͔ 1 , 8s͓3 / 2͔ 1 ͒, then excited by lasers to the autoionizing Rydberg series 3p 1/2 5 npЈ ͓͑1 / 2͔ 0,1 , ͓3 / 2͔ 1,2 ͒ and nfЈ͓5 / 2͔ 2. For the intermediate states of 5sЈ, 7sЈ, and 8s, the npЈ ͓͑1 / 2͔ 0 and ͓3 / 2͔ 2 ͒ series are observed with high intensity but not the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series when the polarization vectors of two light beams are in parallel; but when they are in orthogonal, the npЈ͓1 / 2͔ 0 series disappears, the npЈ͓3 / 2͔ 2 intensity remains, and the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series show up strongly. The intensity distribution of the npЈ series strongly depends on the intermediate state. The spectra of the npЈ series are assigned according to their intensity variation with the polarization vectors. The quantum defects determined for the series npЈ͓1 / 2͔ 0 ͑n =11-57͒, npЈ͓3 / 2͔ 2 ͑n =11-65͒, npЈ͓3 / 2͔ 1 ͑n =11-31͒, and nfЈ͓5 / 2͔ 2 ͑n =9-74͒ are 1.611Ϯ 0.011, 1.683Ϯ 0.013, 1.688Ϯ 0.010, and 0.016Ϯ 0.005, respectively. Our values are in excellent agreement with theoretical prediction. The spectral line shapes of autoionizing Rydberg states are analyzed with a Beutler-Fano profile. Reduced autoionization linewidths for the npЈ͓1 / 2͔ 0 ͑n =11-16͒ series vary in the range 2549-4145 cm −1 , and the nfЈ͓5 / 2͔ 2 ͑n =9-11͒ series in 186-247 cm −1 in reasonable agreement with theoretical prediction.

Autoionization dynamics of even Ar (3p51/2np′,nf′) resonances: comparison of experiment and theory

“…The 7s [1/2] 1 and 8s[3/2] 1 levels (energetic separation of only 6.6 meV) are strongly mixed by configuration interaction. When this interaction is taken into account the calculated spectra for these intermediate levels exhibit lineshapes in satisfactory agreement with the experimental data of Lee et al (2008). The np ARS excited from 4s [1/2] and 5s[3/2] are strongly influenced by the fact that the J = 1 and J = 2 amplitudes are near zero (i.e., are close to a Seaton-Cooper minimum).…”

“…Over the past few years, two-photon excitation studies of ground state Ne (Petrov et al 2006b) and Ar (Lee et al 2008) atoms via several short-lived intermediate, odd-parity J = 1 levels as well as one-photon excitation from the respective mp 5 (m + 1)s, J = 2, 0 metastable levels (Peters et al 2005, Petrov et al 2006a, Wright et al 2008 yielded new results on the lineshapes of the even-parity np J = 0, 1, 2 and nf J = 2 ARS the proper description of which poses a substantial challenge to theory. Calculations of the shapes, widths and energy positions of the Ne(np ) ARS by means of the configuration-interaction Pauli-Fock core-polarization (CIPFCP) method (see, e.g., Peters et al 2005, Petrov et al 2006a, 2009 were found to be in good overall agreement with experimental results (Petrov et al 2006b) only after proper inclusion of an interference effect between the direct 3s|r|np and the intershell 3s|r|3p 3p|V (2p2p)|np amplitudes.…”

“…Stepwise two-photon excitation of Ar atoms with synchrotron and laser radiation has been used to access the np and nf ARS via seven odd-parity J = 1 intermediate levels, namely 3d [3/2] 1 , 5d [3/2] 1 , 5s [1/2] 1 , 7s [1/2] 1 , 6d[1/2] 1 , 6d[3/2] 1 and 8s[3/2] 1 (Lee et al 2008). The spectra excited via the nd and nd levels were all found to be dominated by the nf ARS.…”

“…The np spectra excited from the 5s [1/2] 1 and 8s[3/2] 1 levels are similar in shape to that calculated for 4s [1/2] 1 while in the spectrum excited from the 7s [1/2] 1 level the np J = 0 resonance is less intense and shifted towards lower energies. Lee et al (2008) emphasized the substantial difference between the experimental spectrum recorded from 8s[3/2] 1 (showing a strong peak for the 14p J = 0 resonance) and that calculated by Petrov et al (2006a) for excitation from 4s[3/2] 1 (in which the np [1/2] 0 resonance appears as a weak minimum) and pointed out that a simpler calculation for 4s[3/2] 1 which ignores the interference effect is superior to the more elaborate one because it yields a clear peak for the J = 0 resonance. To resolve this paradox additional calculations for several intermediate levels, including the 7s [1/2] 1 and 8s[3/2] 1 states, must be carried out.…”

Experimental investigation of long-lived Rydberg states in ultracold argon

“…Only low angular momentum states that decay very quickly (picosecond-to-nanosecond time scale) by radiationless autoionization through a core spin flip due to the Rydberg electron-core interaction would be accessible. These autoionizing states (primarily s , p , and d states) in Ar and other noble gases have been studied extensively over many years, primarily through single-and multiphoton highresolution spectroscopy where the linewidth of the observed resonances can be used to extract the lifetime of the states [8][9][10][11][12][13][14][15]. Experimental studies of these low-l states have been compared to theoretical calculations to better understand the dynamics of autoionization [16][17][18][19][20].…”