Potassium spectra in the 700-7000 cm-1 domain: Transitions involving f-, g-, and h-states

Context. The infrared (IR) range is becoming increasingly important to astronomical studies of cool or dust-obscured objects, such as dwarfs, disks, or planets, and in the extended atmospheres of evolved stars. A general drawback of the IR spectral region is the much lower number of atomic lines available (relative to the visible and ultraviolet ranges). Aims. We attempt to obtain new laboratory spectra to help us identify spectral lines in the IR. This may result in the discovery of new excited atomic levels that are difficult to compute theoretically with high accuracy, hence can be determined solely from IR lines. Methods. The K vapor was formed through the ablation of the KI (potassium iodide) target by a high-repetition-rate (1.0 kHz) pulsed nanosecond ArF laser (lambda = 193 nm, output energy of 15 mJ) in a vacuum (10(-2) Torr). The time-resolved emission spectrum of the neutral atomic potassium (K I) was recorded in the 700-7000 cm(-1) region using the Fourier transform infrared spectroscopy technique with a resolution of 0.02 cm(-1). The f-values calculated in the quantum-defect theory approximation are presented for the transitions involving the reported K I levels. Results. Precision laboratory measurements are presented for 38 K I lines in the infrared (including 25 lines not measured previously in the laboratory) range using time-resolved Fourier transform infrared spectroscopy. The 6g, 6h, and 7h levels of K I are observed for the first time, in addition to updated energy values of the other 23 K I levels and the f-values for the transitions involving these levels. Conclusions. The recorded wave numbers are in good agreement with the data from the available solar spectrum atlases. Nevertheless, we correct their identification for three lines (1343.699, 1548.559, and 1556.986 cm(-1)).