Li I spectra in the 4.65–8.33 micron range: high-L states and oscillator strengths

¹ J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague 8, Czech Republic
e-mail: civis@jh-inst.cas.cz
² Voronezh State University, 394693 Voronezh, Russia
e-mail: chernov@niif.vsu.ru
³ State Research Center of Russian Federation Troitsk Institute of Innovation and Fusion Research, 142190, Troitsk, Moscow Region, Russia

Received: 20 June 2012
Accepted: 30 July 2012

Abstract

Context. Infrared (IR) astronomy capacities have rapidly developed in recent years thanks to several ground- and space-based facilities. To take advantage of these capabilities efficiently, a large amount of atomic data (such as line wavenumber, excited-level energy values, and oscillator strengths) are needed. These data are incomplete, in particular, for lithium whose abundances are important for several astrophysical problems.

Aims. No laboratory-measured spectra of Li I have been reported for wavelengths longward of 6.6 microns. We aim to find new Li I lines in the 4.65–8.33 microns range due to transitions between states with high orbital momentum (l ≥ 4) and to determine the excitation energies of these states.

Methods. The Li I lines were studied using the time-resolved Fourier transform infrared spectroscopy of a plasma created by the laser ablation of a LiF target in a vacuum. The classification of the lines was performed by accounting for oscillator strengths (f-values) calculated using quantum defect theory (QDT). The adequacy of QDT for these calculations was checked by comparison with the available experimental and theoretical results.

Results. We report four new Li I lines in the 900–2200 cm^-1 range that allow us to extract the excitation energies of the 6g, 6h, and 7h states of Li I, which have not been measured before. We also provide a large list of QDT-calculated f-values for Li I in the range of 1–20 microns.