Radiative lifetime of the2Pstate of lithium

Abstract

We determine the radial dipole moment between the 2S and 2 P states of atomic lithium by analyzing the long-range vibrational eigenenergies of the singly excited diatomic molecule. The result can be expressed in terms of the 2 P 1/2 radiative lifetime of 7 Li, which is found to be 27.102(2)(7) ns. This result agrees with most current atomic-structure calculations and resolves the long-standing disagreement with previous experiment. The current level of precision is sensitive to relativistic effects in the atomic-structure calculation and to non-Born-Oppenheimer and radiation retardation effects in the molecule. ͓S1050-2947͑96͒50307-0͔ PACS number͑s͒: 32.70. Cs, 34.20.Cf, 31.30.Jv Atomic radiative lifetimes are known to be sensitive tests of atomic-structure calculations. The relatively simple structure of atomic lithium makes it a viable candidate for testing the various ab initio techniques which, in recent years, have grown in both sophistication and accuracy ͓1-8͔. A recent calculation of the 2S↔2 P nonrelativistic oscillator strength by Yan and Drake ͓8͔ has an estimated uncertainty of only 1.0ϫ10 Ϫ6 . Experimentally, the most precisely stated measurement of a radiative lifetime for a multielectron atom is the measurement of the 2 P lifetime of lithium by Gaupp et al. ͓9͔, with a one standard deviation uncertainty of 1.5ϫ10 Ϫ3 . Unfortunately, the experimental result and most calculations disagree by more than four standard deviations. Resolution of this large discrepancy is motivated by the need to apply atomic-structure calculations to more complicated atoms. In particular, atomic theory is crucial for interpreting parity violation in experiments with cesium ͓10͔. Clearly, there is a strong need for finding alternative methods of precisely measuring this value.Radiative dipole moments can be determined by analyzing the spectra of long-range, singly excited diatomic molecules. Photoassociative spectroscopy of ultracold atoms is a powerful tool for probing these high-lying molecular vibrational states ͓11͔. In previous work, we used this technique to observe the highest vibrational levels of the A 1 ⌺ u ϩ state of 6 Li 2 and 7 Li 2 ͓12͔. The long-range portion of this potential arises from a resonant dipole-dipole interaction that has the functional form V(R)ϭϪC 3 /R 3 . The coefficient C 3 is inversely proportional to the 2 P atomic radiative lifetime, , by ͓13͔where is the wavelength of the atomic transition.In a previous publication, we constructed a model potential for the 1 3 ⌺ g ϩ manifold from a variety of ab initio and experimental sources ͓14͔. Eigenvalues from this model were calculated as a function of C 3 and fitted to the corresponding data. The estimated uncertainty of 6ϫ10 Ϫ3 was due to systematic uncertainties associated with parts of the model known only through ab initio calculation. However, since then, Linton et al. ͓15͔ have used Fourier transform spectroscopy of the A 1 ⌺ u ϩ state to measure a range of vibrational levels for which the highest-lying ones overlap the lower part of the...

High-precision calculations of van der Waals coefficients for heteronuclear alkali-metal dimers

“…In accurate experiments McAlexander et al [26] reported a lifetime of the 2p state of 27.102(9) ns (an accuracy of 0.03%) and Martin et al [27] reported 27.13(2) ns. In our calculations we employ the more precise value from Ref.…”

“…In our calculations we employ the more precise value from Ref. [26]; in the subsequent error analysis we arbitrarily assigned an error bar of twice the quoted value of Ref. [26], so that the two experiments are consistent.…”

Calculation of radiative corrections toE1matrix elements in the neutral alkali metals

“…This has allowed the determination of the lifetime of the 2p 1/2 state of lithium as 27.102(7) ns [3], the lifetime of the 3p 3/2 state of sodium as 16.230(16) ns [4], the lifetimes of the 4p 1/2 and 4p 3/2 states of potassium as 26.69(5)ns and 26.34(5) ns [5], the lifetimes of the 5p 1/2 and 5p 3/2 states of rubidium as 27.75(8) ns and 26.25 (8) ns [6], and the lifetimes of the 6p 1/2 and 6p 3/2 states of cesium as 34.88(2) ns and 30.462(3) ns [7]. (References to other experimental determinations of lifetimes, some of which are of higher accuracy, can be found in the above references.…”

Improved LeRoy–Bernstein near-dissociation expansion formula, and prospect for photoassociation spectroscopy

“…Indeed, a precise τ value was obtained using a pure long-range expansion of the 0 − g (s + p 3/2 ) potential curve of dialkalis [35,36,37,38].…”