Emission spectra of alkali-metal [Formula Presented] exciplexes in cold helium gas

We have observed emission spectra of excimers and exciplexes composed of a light alkali-metal atom in the first excited state and [Formula Presented] atoms [[Formula Presented] [Formula Presented] [Formula Presented] [Formula Presented] and [Formula Presented] [Formula Presented] in cryogenic He gas (the temperature [Formula Presented] in the spectral range from the atomic D lines to [Formula Presented] Differently from exciplexes with heavier alkali-metal atoms, the spectra for the different number of He atoms were well separated, so that their assignment could be made experimentally. Comparing with the spectra of [Formula Presented] we found that the infrared emission spectrum of the K atom excited in liquid He was from [Formula Presented] To confirm the assignment, we have also carried out ab initio calculation of adiabatic potential curves and peak positions of the emission spectra of the exciplexes.