Natural radiative lifetimes in the perturbed 6snd 1 D 2 sequence of barium

Abstract

Natural radiative lifetimes in the perturbed 6sns ~D 2 (n= 12-30) sequence of barium have been measured using the PUMOLS (PUlse-MOdulated Laser Spectroscopy) method, which incorporates pulse-modulation of a CW dye-laser beam and delayed coincidence techniques. Principal perturbers are the 5d 7d 3F 2 and ~D 2 states. Lifetimes were also measured for these shortlived valence states, which through configuration mixing cause drastic decreases in lifetime values in the region of perturbation of the 6snd 1D z sequence. Two-step laser excitation from the ground 6s 2 ~So state via the 6s 6p 1p~ state was employed. Special care was taken to determine the influence of black-body radiation transitions on the measured lifetimes.

Lifetimes along perturbed Rydberg series in neutral thallium

“…Similar perturbations are observed in many different situations like in the alkaline-earth atoms where perturbations of Rydberg series by isolated levels considerably modify the lifetime values (see, e.g. Bhatia et al (1981) and Aymar et al (1982)). Baylis (1979a, 1979b) have demonstrated that correlation effects between valence and core electrons can be approximated by core-polarization corrections in relativistic single-configuration Hartree-Fock computations of oscillator strengths.…”

Radiative-lifetime measurements and calculations of odd-parity highly excited levels in Ba i

“…j Reference [21]. k Reference [15]. l Affected by strong cancellation effects that lengthen the calculated lifetime.…”

“…Experimental measurements of radiative lifetimes for some even-parity levels [13][14][15][16][17][18][19][20][21] and calculations for the 6snf 3 F 2 (11 n 35) Rydberg series and some 6s6p, 6s7p, 5d5p, and 5d6p levels [22,23] have been reported. But because it is difficult or impossible to excite most of the high-lying odd-parity levels from the ground level 1 S 0 and because the lowest metastable levels 6s5d 3 D J (J = 1 to 3) located above 9000 cm −1 are difficult to populate in a thermal atomic beam, direct lifetime measurements for such levels are scarce.…”

Zeeman effect in the perturbed 6s n d 1,3 D 2 sequences of Ba-I: test of MQDT wavefunctions

“…In particu-tar, the wavefunctions of the 6s 14d 1, 3Dz and 5d7d 3k~ level have to be tested for ability to describe lifetime [5] and hyperfine-structure data [11]. In fact it is very difficult for MQDT to well parametrize the localized perturbation occuring in energy ranges, where Rydberg levels are widely separated and the new wavefunctions obtained for the 6s 14d 1,3D2 level, although consistent with gj measurement, are certainly less reliable than wavefunctions for high-lying levels.…”

“…It is of considerable interest to test to what extent MQDT wavefunctions can be used for reliable prediction of various quantities. Recently, three independent investigations of natural lifetimes in the perturbed 6snd I'3D z sequences of Ba were performed [5][6][7]. Close to the perturbing Ba 5 d 7 d 3F2, and especially the 5 d 7 d 1D 2 state, strong resonant changes in the measured lifetimes are observed.…”