Observations of potassium in the tenuous lunar atmosphere

Observations of neutral potassium (K) in the tenuous lunar atmosphere are described. An echelle spectrograph, CCD, and data acquisition system are used to obtain emission spectra of neutral K atoms in the lunar atmosphere as observed by the 1.54 telescope at the Catalina Observatory at first quarter the night of April 29, 1989. A table of relevant lunar atmosphere parameters summarizes the results of the investigation. It is found that the number density at the surface is 9.5 + or - 1 atoms per cu cm and that there is a large nonthermal component and a deficiency of atoms equilibrated to the surface temperature. The calculated thermalization rate of the nonthermal component through encounters with the lunar surface gives a source of strength for the thermal component factor of 7 greater than loss by photoionization. Possible explanations for the low thermalized population observed are considered.